DE102005045592B4 - Frequency converter unit - Google Patents

Abstract

A frequency converter unit comprising: a first polyphase filter having a first input and a second input and an output, the first polyphase filter adapted to provide at its output a filtered signal in response to an amplitude, a frequency and a phase relationship at its first and second outputs generate second input applied signals; a frequency converter having a frequency converter input coupled to the output of the first polyphase filter and a first frequency converter output and a second frequency converter output, the frequency converter means being adapted to provide signals having a signal component based on the signal at the frequency converter input at the first frequency converter output and the second frequency converter output which are shifted in frequency from the signal at the frequency converter input; and a second polyphase filter having a first input coupled to the first frequency converter output and a second input coupled to the second frequency converter output and an output, wherein the second polyphase filter is configured to ...

Description

The present invention generally relates to a frequency converter unit, in particular to a frequency converter unit, in which a first polyphase filter is connected upstream of a mixer device and in which a second polyphase filter is connected downstream of the mixer device.

In a variety of information technology and telecommunications systems signals must be selected and / or transferred to another frequency range. Such signal processing, which represents a signal conversion, is used in many fields of information or telecommunications, for example in wireless telemetry applications, mobile phones or wireless data transmission.

Various receiver concepts are known in which a comparatively high effort is required in each case to suppress image frequencies, which are undesirably reproduced on an intermediate frequency range during a frequency conversion. In order to achieve a good intermediate frequency suppression, such receiver arrangements require expensive high-frequency filters for image frequency suppression or multiple frequency conversion. This increases the complexity of a high-frequency receiver as well as the power consumption. In addition, the required (partly tunable) image rejection filters are difficult to implement integrated.

Therefore receiver concepts have been developed in which an image frequency rejection in the intermediate frequency range occurs. In these, a complex mixer is used for the frequency conversion, which generates an in-phase and a quadrature signal, and an analog or digital polyphase filter is connected downstream. The image rejection then takes place in the polyphase filter.

In the patent EP 1 247 339 B1 ("Polyphase filter") is in 1 describes the architecture of a low IF receiver with a polyphase filter. The task of the filter is the selection of the desired frequency range and the suppression of signals from unwanted frequency ranges.

The use of a polyphase filter in the circuit arrangement shown makes it possible in particular to suppress the image frequency range with little effort.

In shifting a signal to a different frequency position by mixing with a suitable high-frequency signal gives an image frequency range which is mixed to the same frequency position as the actual signal to be received. If a signal is present in this image frequency range, it is at the same frequency as the desired signal after mixing and causes interference. A polyphase filter, at the inputs of which both the signal itself and a second signal, which is generated by a phase shift of 90 ° from the original signal, is able to extract the signal from the desired frequency range from the signal from the image frequency range also after to separate the mixture. The generation of the second signal is typically done by an I / Q demodulator or modulator.

The image frequency suppression by the I / Q demodulator or modulator downstream polyphase filter is based on the ability to distinguish signals with the same frequency position, but different phase position to each other. This ability depends to a large extent on how accurate the phase difference is at the two inputs of the polyphase filter. Even small deviations from the ideal size reduce the selection ability of the filter.

The accuracy with which, for example, current typical I / Q demodulators can produce the two inputs to a polyphase filter limits the possible selection of the image frequency range to about 35 dB.

In addition, in the current state of the art (e.g. EP 1 247 339 B1 ) only first order polyphase filters are described. To increase the edge steepness of such filters or to improve the selection, the series connection of several polyphase filters is necessary. This leads to an increased demand for components, especially when active filters are used which require operational amplifiers with high performance.

The WO 02/093732 A2 describes an integrated tuner circuit that uses a double frequency conversion. The tuner includes a first polyphase filter on the input side of a full-complex mixer and a second polyphase filter on the output side of the full-complex mixer.

The DE 698 20 376 T2 shows a receiver with a frequency converter to derive a plurality of intermediate polyphase signals from an input signal of the receiver. The receiver includes a polyphase filter for deriving filtered polyphase signals from the intermediate polyphase signals. Furthermore, the receiver comprises a further frequency converter in order to obtain a plurality of the filtered polyphase signals derive further intermediate polyphase signals. The receiver comprises a further polyphase filter for deriving further filtered polyphase signals from the further intermediate polyphase signals. Either the polyphase filter or the further polyphase filter is provided to attenuate signals above a first frequency. Either the polyphase filter or the further polyphase filter is further provided to attenuate signals below a second frequency. The first frequency and the second frequency are essentially zero.

The short manuscript for the lecture "Signal Presentation" by M. Lang (Technical University of Munich, Chair of Human-Machine Communication, May 1994) describes, among other things, properties of a continuous-time Fourier transformation.

The publication "A Low-Voltage Full-Differential BiCMOS Op Amp for Polyphase Filter" by G. Blakiewicz and J. Jakusz describes a fully-differential low-voltage operational amplifier for a polyphase filter for mobile communications receivers. Furthermore, the cited publication describes an implementation of a portion of a polyphase filter as the active RC circuit.

The publication "CMOS Mixers and Polyphase Filters for Large Image Rejection" by F. Behbahani et al. a. describes different architectures of mixers and polyphase filters. Furthermore, said publication describes how the mixers and polyphase filters can be used to suppress image frequencies in transmitters and receivers. Among other things, the cited publication describes analog complex filters, polyphase analog filters, image frequency rejection techniques, and generation of quadrature signals. Furthermore, some architectures of radio receivers are given.

The publication "Digital Receivers and Transmitters Using Polyphase Filter Banks for Wireless Communications" by F.J. Harris et al. a. describes digital receivers using polyphase filters. The cited document shows various receiver architectures.

The publication "An Analog Integrated Polyphase Filter for a High Performance Low-IF Receiver" by J. Crols and M. Steyaert describes a realization of a first-order polyphase filter. The realization takes place as an active RC circuit.

It is an object of the present invention to provide a frequency converter unit with improved image rejection on the basis of polyphase filters.

This object is achieved by a frequency converter unit according to claim 1.

The present invention provides a frequency converter unit having a first polyphase filter having a first input and a second input, and a first output and a second output, wherein the first polyphase filter is adapted to at its first output and its second output filtered signals in response to an amplitude to generate a frequency and a phase relationship of signals applied at its first and second inputs, a frequency converter having a first frequency converter input coupled to the first output of the first polyphase filter and a second frequency converter input coupled to the second output of the first polyphase filter , and a first frequency converter output and a second frequency converter output, wherein the means for frequency conversion is designed to, due to the signals at the first frequency converter input and the second frequency converter input to the first Frequency converter output and the second frequency converter output to provide signals with a signal component which are shifted relative to the signals at the first frequency converter input and the second frequency converter input with respect to a frequency, and a second polyphase filter having a first input which is coupled to the first frequency converter output, and a second input coupled to the second frequency converter output and an output, the second polyphase filter being adapted to generate an output signal at its output in response to an amplitude, a frequency and a phase relationship of the signals applied to its first and second inputs; wherein the first polyphase filter and the second polyphase filter are configured to individually or in cooperation desired Nutzfrequenzsignale that mapped at a frequency conversion in the Frequenzumsetzereinrichtung to a predetermined frequency interval w ground to transmit from the first and the second input of the first polyphase filter to the output of the second polyphase filter, and to attenuate unwanted image frequency signals which are mapped to the predetermined frequency interval in the frequency conversion in the frequency converter.

It is the core idea of the present invention that a frequency converter unit has an improved image rejection compared to conventional arrangements, if the actual frequency converter means a is preceded by the first polyphase filter, and when the frequency converter further a polyphase filter is connected downstream, which receives two signals from the frequency converter. This enables continuous phase-selective signal processing. So there are two polyphase filters are used, wherein one of the frequency converter is connected upstream and one of the frequency converter downstream. Both polyphase filters contribute to the image rejection, so that the image rejection over conventional arrangements is significantly improved.

Polyphase filters are complex unbalanced bandpass filters that have only one passband on the positive or negative frequency axis. This provides additional image rejection. While a traditional bandpass filter has a passband for both the positive and the negative spectral half, in a polyphase filter, a pass band, that is, either the positive or negative band, is completely suppressed. The suppression causes a disappearance of the image frequency, so that no complex mixer or no intermediate frequency is required for mixing in the baseband. In practice, however, the passband on the negative (or positive) frequency axis does not completely disappear. The closer the image frequencies are to the useful signal, the worse the image rejection. Meaningful frequency planning is nevertheless necessary. However, 15 to 20 dB of image rejection are usually achievable. A complex mixture followed by polyphase filtering provides an additional 25 to 35 dB, so that an image rejection of about 50 dB can be achieved.

The polyphase filter in front of the frequency converter, the z. B. may be a complex mixer, thus contributes significantly to the improvement of the image rejection.

It is an advantage of a frequency converter unit according to the invention, which can be significantly improved with the new topology, the system properties over conventional structures. The suppression of the image frequency range in low IF architectures can be increased from about 35 dB to over 50 dB when using commercial components. The improved image rejection makes it possible to first build receiver circuits based on commercially available I / Q modulators and mixers, while with the same components using a conventional network topology, the image rejection does not meet the practical requirements.

Thus, the present invention enables the implementation of a telecommunications signal from one frequency layer to another using a novel network topology, which provides significant advantages over the prior art. The application of a frequency converter unit according to the invention is not limited to I / Q demodulators, but can also be used in I / Q modulators. Thus, the network topology according to the invention allows both the reception and the generation of signals. Not only image frequencies, but also influences of adjacent channels are suppressed.

In a preferred embodiment, the first polyphase filter further includes a second output, wherein the first polyphase filter is configured to receive filtered signals at its first output and at its second output in response to an amplitude, a frequency, and a phase relationship at its first and second To generate input to adjacent signals. The frequency converter means preferably further comprises a second frequency converter input coupled to the second output of the polyphase filter, the frequency converter means being arranged to provide signals at one of the first frequency converter input and the second frequency converter input at the first frequency converter output and the second frequency converter output Provide signal component which are shifted relative to the signals at the first frequency converter input and the second frequency converter input with respect to a frequency. Such an embodiment offers the advantage that two phase-shifted signals are transmitted from the first polyphase filter to the frequency converter device. This further enhances image rejection by avoiding the imperfections that result when a signal is converted to its in-phase and quadrature components and back.

In a preferred embodiment, the first polyphase filter is preceded by a signal conversion device which is designed to receive a real-valued input signal and, due to this, to provide two signals shifted relative to one another in phase relationship with the first input and the second input of the first polyphase filter. Such a device is advantageous if only a real-valued signal is available at the input of the frequency converter device. The first polyphase filter can thus be operated even if as input signal not already two mutually phase-shifted signals are present. This is z. B. in receiver circuits of the case. It should be noted, however, that the use of the signal conversion device is not necessary. Rather, it is possible, in particular in the generation of signals, for the frequency converter unit to be provided with two signals phase-shifted with respect to one another, for example from a digital signal processing device.

If a signal conversion device is necessary, in a preferred embodiment it may comprise a phase shift device which is designed to generate a phase shifter output signal delayed by a predetermined delay time on the basis of a phase shift input signal. In a preferred embodiment, this delay time is variably adjustable. The phase shifter represents an advantageous and practical with moderate effort implementable device to generate two mutually phase shifted signals. Such mutually shifted signals can then be processed in a polyphase filter. The adjustability of the phase shift or the delay time is advantageous in order to be able to adapt the phase shift device to different frequencies. A fixed delay time results in a change of the frequency in a changed phase shift. If a predetermined phase shift is to be achieved, it is expedient for the delay time to be adapted to the frequency.

Moreover, it should be mentioned that adjustable phase shifters or adjustable delay lines are available as commercial components, which reduces the implementation effort for a frequency converter unit according to the invention.

In a further preferred embodiment, the signal conversion means may comprise a third polyphase filter having an input and a first output and a second output adapted to output signals having a predetermined phase relationship to each other at its input at its first output and its second output due to a signal at its input , Thus, another polyphase filter can be used to generate two signals with a predetermined phase shift at the inputs of the first polyphase filter. According to a preferred embodiment, the third polyphase filter has an all-pass characteristic which is designed such that the amplitude of the signals at its first output and at its second output are equal and independent of a frequency of the signal at its input within a predetermined tolerance range the polyphase filter for a larger frequency range ensure a predetermined phase relationship between the two output signals, as is possible using a conventional phase shifter or delay device. The tolerance range should preferably not be greater than ± 3 dB.

In a further preferred embodiment, the first polyphase filter is a bandpass filter. This makes it possible to suppress signals whose frequency is outside a useful frequency range. Such signals can then automatically no longer appear as mirror frequencies. In addition, the insertion of a bandpass filter helps to avoid overloading of subsequent stages by strong spurious signals outside the useful frequency range. Thus, the design of the first polyphase filter as a band-pass filter contributes to both image rejection and to improve the immunity of the entire frequency converter unit to signals outside the useful frequency range.

In a preferred embodiment, the first polyphase filter is an active filter that includes active devices configured to amplify an electrical signal. If the frequencies to be processed are sufficiently low, the first polyphase filter preferably comprises one or more operational amplifiers. Operational amplifiers can be used advantageously at frequencies below 100 MHz for the realization of active amplifiers or filters. The circuit complexity is significantly reduced by the use of integrated circuits. A circuit design is mostly possible based on the assumption of the ideal operational amplifier, wherein the real behavior of the operational amplifier in a circuit simulation can be taken into account. In many cases it is possible, starting from initial values for the component values, which are based on the assumption of an ideal operational amplifier, to carry out an optimization, so that a desired transmission characteristic of a polyphase filter can also be achieved with a real operational amplifier.

If the frequencies to be filtered are so high that an operational amplifier can no longer be usefully used, then it is preferred that the first polyphase filter is a passive filter. Passive filters can be realized up to the highest frequencies in the millimeter-wave range, and it is possible to keep losses very low. The coupling of the two signal paths is possible by means of suitable analog coupling circuits or suitable coupling devices between a plurality of waveguides.

Preferably, the first polyphase filter comprises a filter bank with a plurality of individual filters, which can be switched on by a switching device optionally between the inputs and the outputs of the first polyphase filter. Such an arrangement has the advantage that the first polyphase filter can be designed for a very large frequency range. In particular, when using a filterbank having a plurality of individual filters, it is possible to achieve a frequency ratio of up to 1:30 and more between the lower cutoff frequency and the upper cutoff frequency of a bandpass filter. By the division into several individual filters, the realization of a single filter can be facilitated. In particular, a very wide bandpass can be realized through the entire filter bank, which nevertheless has a sufficiently sharp filter characteristic at the boundaries of the passband. Furthermore, it is advantageous to design the individual bandpass filters of the filter bank such that the frequency ranges overlap. In this case it is ensured that the entire frequency range is safely covered. In a further embodiment, the first polyphase filter comprises a wideband bandpass filter whose bandwidth is greater than its center frequency. Such a design makes it possible to process very broadband signals or cover a large frequency range with a single bandpass filter. This considerably reduces the circuit complexity.

In a further preferred embodiment, the first polyphase filter and / or the second polyphase filter have a filter order that is at least equal to 2. The use of high order filters allows good selectivity of the first polyphase filter and the second polyphase filter. Thus, both noise and image frequency signals can be suppressed more effectively than is possible with filters with a lower filter order. In particular, it is advantageous if both the first polyphase filter and the second polyphase filter have an order which is at least equal to 2. In this case, the filter effect can be evenly distributed to both filters. This allows for optimal system design. Already before the actual frequency converter device, high-order filtering takes place, whereby strong interference signals are kept away from the non-linear frequency converter device and, in addition, the image frequency suppression can be improved. Higher-order filters can be implemented particularly advantageously as polyphase filters because they are not dependent on the presence of inductive components. Thus, both the quality of a polyphase filter can be higher than that of a conventional filter and an integrated implementation is more easily possible. Thus, on the high-frequency side, that is before the frequency converter, a filter of high quality can be realized. In particular, suppression of spurious signals results in reduced cross-modulation products. The symmetry of the arrangement with respect to the two filter branches further brings an improved large-signal characteristic with it. This is particularly advantageous in connection with non-linear frequency converter elements.

In a further preferred embodiment, the first and / or second polyphase filter is a higher order polyphase filter having a first signal input and a second signal input for receiving a first input signal and a second input signal and a first first order filter element, a second first order filter element, a third filter element first order and a fourth filter element of first order, wherein an input signal of the first filter element is dependent on the first input signal, an output signal of the second filter element and an output signal of the fourth filter element, wherein an input signal of the third filter element from the second input signal, from the output signal of the second Filter member and is dependent on the output signal of the fourth filter element, wherein an input signal of the second filter element of an output of the first filter element and of the output signal of the fourth filter element dependent wherein an input signal of the fourth filter member is dependent on an output signal of a third filter member and the output signal of the second filter member, and wherein the polyphase filter is adapted to vary in response to a frequency and an amplitude of the first input signal and the second input signal a phase relationship between the first input signal and the second input signal to produce a polyphase filter output signal. Such a design of a polyphase filter has the advantage that higher-order filters can be achieved with little circuit complexity. The implementation cost is lower than in the series connection of several first-order filters. There is also much more freedom in the choice of poles and zeros. Thus, higher-slope filters can be designed, or filters with a better adapted to the respective requirements transmission characteristic.

Preferred embodiments of the present invention will be explained in more detail below with reference to the accompanying drawings. Show it:

1 a block diagram of a receiver front end with a frequency converter unit according to the invention according to a first embodiment of the present invention;

2 a detailed block diagram of a receiver front end with a frequency converter unit according to the invention according to the first embodiment of the present invention;

3 a block diagram of a polyphase filter with a signal conversion device for use in a frequency converter unit according to the invention;

4 a detailed block diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention;

5 a simplified circuit diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention; and

6 a detailed circuit diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention.

1 shows a block diagram of a receiver front end with a frequency converter unit according to the invention according to a first embodiment of the present invention. The receiver frontend is in its entirety with 10 designated. At the entrance of the receiver frontend 10 There is a high frequency amplifier with adjustable gain 12 (GCA). Downstream of this is a complex filtering network 14 , The filter network 14 provides an in-phase signal I ₁ and a quadrature signal Q ₁ to a complex mixer 16 , The complex mixer continues to receive the output signal of a local oscillator 18 fed. At the exit of the complex mixer 16 is a second in-phase signal I ₂ and a second quadrature signal Q ₂ available, which a second complex filtering network 20 is supplied. The complex filtering network 20 is a facility 22 downstream of the analog / digital conversion, which may include one or two analog-to-digital converter depending on the design. The output signal 24 the analog / digital converter device 22 is another digital signal processing device, which is not shown here, available.

Based on the structural description of the receiver frontend 10 The following describes how it works. A received signal 30 that from an antenna 32 is supplied to the high frequency amplifier 12 supplied with adjustable gain. The gain is controlled so that the sensitivity of the receiver frontend 10 is as large as possible, without any component in the signal path is overdriven by too strong a signal. The high-frequency control amplifier 12 Downstream is a first complex filtering network 14 which is designed as a bandpass filter. The filter network becomes a real high frequency signal 36 fed, the same as that through the high-frequency amplifier 12 amplified received signal 30 is. The first complex filtering network 14 comprises a signal conversion device, which consists of the real high-frequency signal 36 generates two signals with a given phase relationship. These then become the two branches of the complex filtering network 14 fed. There is a coupling between the two branches, so that the complex filter network realizes a polyphase filter. The first in-phase signal I ₁ and the first quadrature signal Q ₁ , both provided by the polyphase filter of the first complex filtering network, are dependent on the amplitude and frequency of the polyphase filter input signals as well as the phase relationship between the input signals of the first polyphase filter. Thus, the first polyphase filter provides a filter characteristic that is different from that of a conventional filter in that the output is dependent on the phase relationship of two signals. According to a mathematical formalism, the first polyphase filter may be part of the first complex filtering network 14 is to be described by assuming a transmission characteristic asymmetric with respect to the frequency zero. In such a model, a distinction is made between positive and negative frequencies. A suitably designed polyphase filter can in this case enable the suppression of image frequencies that arise during frequency conversion. The first complex filtering network 14 is a complex mixer 16 downstream, which is a signal from a local oscillator 18 receives. The complex mixer 16 is responsible for the actual frequency conversion and includes several non-linear elements. It should be noted that the complex mixer 16 receives a first in-phase signal I ₁ and a first quadrature signal Q ₁ and generates a second in-phase signal I ₂ and a second quadrature signal Q ₂ . There is a frequency shift between the first and second in-phase signal as well as between the first and the second quadrature signal. In addition, a reversal of the sidebands may occur, that is, a first frequency greater than a second frequency is mapped to a first frame rate that is less than a second frame rate. However, it is also possible that the sidebands are not reversed in the frequency conversion. The complex mixer 16 Downstream is a second complex filtering network 20 which in turn comprises a polyphase filter. That is, there are two coupled filter branches to which different input signals are supplied. By way of example, one filter branch can be supplied with the second inphase signal and the second filter branch with the second quadrature signal. The second polyphase filter contained in the second complex filter network can hereby take on several tasks. With a suitable design, it may serve to further improve the image frequency rejection occurring in the frequency conversion mirror frequencies. In addition, the second complex filtering network with the second polyphase filter can perform the function of a bandpass filter that passes only one frequency band at an interval around the intermediate frequency. The intermediate frequency is typically much lower than the receiving frequency, so that the intermediate frequency signal can be converted into a digital data stream and processed digitally. It is also conceivable that the intermediate frequency is equal to zero, so that the second polyphase filter is a low-pass filter. An intermediate frequency suppression is no longer required. The conversion of intermediate frequency signals present at the outputs of the second polyphase filter into digital signals is effected by an analogue / digital converter device 22 , Depending on the requirements, it is possible to convert only one output signal of the second polyphase filter or both output signals of the second polyphase filter into a digitized signal. Accordingly, the analog / digital converter device 22 comprise one or two analog / digital converters. Even if both output signals of the second polyphase filter to be digitized, so u. U. an analog / digital converter to capture the two signals in time multiplex. This reduces the circuit complexity. After the analog / digital conversion is a digitized intermediate frequency signal 24 available, which can be further processed in a digital signal processing circuit. In particular, a digital frequency conversion or a digital filtering can take place. Also signal demodulation can be achieved by the digital circuitry.

Thus, the receiver frontend shown is 10 in its entirety, a high frequency signal from an antenna 32 to receive in the frequency and to provide a filtered portion of the spectrum of the input signal in digitized form. The two complex filter networks 14 and 20 each comprising a polyphase filter and one of which is the complex mixer 16 upstream and one of which is the complex mixer 16 in the arrangement shown enable a signal filtering and a negative pressure of image frequencies that occur in the frequency conversion conventionally.

2 shows a detailed block diagram of a receiver front end with a frequency converter unit according to the invention according to a first embodiment of the present invention. The receiver frontend is in its entirety with 110 designated. It includes a tuner 112 as well as a facility 114 for analog / digital conversion. The tuner 112 has a high frequency signal input 120 on. The signal present there is a high-frequency amplifier 122 fed. The output signal of the high frequency amplifier 122 is decomposed into two components, the two inputs 124 . 126 a first polyphase filter 128 be supplied. The output signals 130 . 132 of the first polyphase filter 128 become the two inputs of a complex mixer 138 fed. Its output signals 140 . 142 become an intermediate frequency amplifier device 148 fed. The amplified intermediate frequency signals 150 . 152 become a second polyphase filter 158 supplied as input signal. The two signals 160 . 162 at the outputs of the second polyphase filter 158 then the facility 114 fed to the analog / digital conversion. At the output is a digitized in-phase signal I and a digitized quadrature signal Q available.

That by the high-frequency amplifier 122 amplified high frequency signal from the high frequency signal input 120 is divided into two components. These will be the first entrance 124 of the first polyphase filter 128 as well as the second entrance 126 of the first polyphase filter 128 fed. The first polyphase filter 128 includes a first filter branch 180 and a second filter branch 182 , Between the two branches 180 . 182 there is a coupling 184 , The first polyphase filter 128 is designed in its entirety as a bandpass filter. The first and second output signals 130 . 132 of the first polyphase filter 128 become the complex mixer 138 fed. The complex mixer 138 includes four individual mixers 190 . 192 . 194 . 196 , The first single mixer 190 and the second single mixer 192 becomes the first output signal 130 of the first polyphase filter 128 fed. The third single mixer 194 and the fourth single mixer 196 becomes the second output signal 132 of the first polyphase filter 128 fed. Furthermore, the complex mixer includes 138 a local oscillator 200 , as well as a phase shifter 202 , which is an in-phase oscillator signal 204 and a quadrature oscillator signal shifted from this by 90 ° 206 generated. The in-phase oscillator signal 204 becomes the first single mixer 190 and the third single mixer 194 supplied as oscillator signal while the quadrature oscillator signal 206 the second single mixer 192 and the fourth single mixer 196 is supplied as an oscillator signal. In a first summing element 210 become the output signals of the first single mixer 190 and the fourth single mixer 196 sums up, being the first output signal 140 of the complex mixer 138 arises. In a second summing element 212 become the output signals of the second single mixer 192 and the third single mixer 194 summed, with the second output 142 of the complex mixer 138 arises. The two output signals 140 . 142 of the complex mixer 138 are then in an intermediate frequency amplifier device 148 that have two separate intermediate frequency amplifiers 220 . 222 includes, amplifies. The two amplified intermediate frequency signals 150 . 152 are then the two inputs of a second polyphase filter 158 fed. The second polyphase filter 158 again comprises two filter branches 230 . 232 between which a coupling 234 consists. The filtered output signals 160 . 162 of the second polyphase filter 158 then become a facility 114 fed to the analog / digital conversion. In the embodiment shown here, the device comprises 114 for the analog / digital conversion two separate analog / digital converters 240 . 242 which generate a digitized in-phase signal I and a digitized quadrature signal Q.

Based on the structural description, the following is the operation of the receiver frontend 110 described. On the high-frequency amplifier 122 followed by a first polyphase filter 128 which has, with respect to an input signal in a complex representation, a filter characteristic which is asymmetrical with respect to the frequency zero point. The entrances 124 . 126 of the first polyphase filter 128 two components of the amplified high-frequency input signal are supplied, which are shifted from each other in phase. The phase shift is in this case achieved either by a phase shifter or by another polyphase filter, which is connected as a phase shifter. The first polyphase filter contributes to image frequency rejection of the receiver front end 110 about 15 to 20 dB at. The on the first polyphase filter 128 following complex mixers 138 , the four single mixer 190 . 192 . 194 . 196 includes, allows the actual frequency conversion. Due to the complex structure of the mixer as well as a suitable combination of the mixed signals in summators 210 . 212 Also carries the complex mixer (quadrature mixer) about 25 to 30 dB for image frequency rejection of the receiver front end 110 at. Another contribution to image rejection is provided by the second polyphase filter 158 , the amplified output signals of the complex mixer 138 be supplied. Also the transfer characteristic of the second polyphase filter 158 is dependent on a phase difference between the first amplified intermediate frequency signal 150 and the second amplified intermediate frequency signal 152 which are fed to him as input signals. Due to the complex mixture, the phase shift occurring for a desired useful frequency signal is opposite to the phase shift occurring for an image frequency signal to be suppressed. These phase shifts may be due to the second polyphase filter 158 be used for distinguishing and separating Nutzfrequenzsignalen and image frequency signals.

It should also be noted that both the first polyphase filter 128 as well as the second polyphase filter 158 not only for image rejection, but also for signal selectivity. The first polyphase filter 128 is therefore designed as a bandpass, only to the receiver frontend 110 to let the frequency range to be used pass. An example of this frequency range is the shortwave range from 1 MHz to 30 MHz. Such a selection protects the one on the first polyphase filter 128 the following stages against an override by signals that are outside the frequency range to be used. The complex mixer 138 takes over the actual frequency conversion and contributes further to the image frequency suppression. Task of the intermediate frequency amplifier device 148 it is, output signals of the complex mixer 138 to bring to a predetermined advantageous level, so that the further processing stages can operate in an optimal operating range. The second polyphase filter 158 finally removes any image frequency signals that are not completely suppressed in the complex mixture, and at the same time filters the intermediate frequency, so that only a predetermined intermediate frequency range, the second polyphase filter 158 can happen. The intermediate frequency is typically chosen so low that a digital further processing of the intermediate frequency signals is possible. There are both receiver architectures with low intermediate frequency and receiver architectures with the intermediate frequency zero. In the first case, the second polyphase filter is 158 In the second case, the second polyphase filter is designed as a low-pass filter that allows low frequencies to pass through and attenuates higher frequencies. The second polyphase filter 158 Downstream is a facility 114 for analog / digital conversion. This finally enables the transition from analog output signals of the second polyphase filter to digital signals.

The present embodiment can be changed in a wide range. Thus, it is possible to use only one output of the first polyphase filter. In this case, the circuit characteristics only slightly deteriorate, and suppression of an image frequency range by the first polyphase filter can still be achieved. The reason for this is the asymmetrical frequency response of the Polyphase. It is also possible to use each of the two output signals 130 . 132 of the first polyphase filter to shift separately in frequency, so that a total of only two individual mixers are required. The complex mixer is thus reduced to two independent individual mixers. This brings a significant simplification of the circuit with it, since two individual mixer can be saved. Nevertheless, even such an arrangement provides a good suppression of the image frequencies.

On the other hand, with respect to the frequency shift, only one output of the first polyphase filter is possible 128 to use. The complex mixer suitably used in this case then has an input and two outputs, the output signals having a phase offset of 90 ° and thus representing an in-phase component and a quadrature component. The input of the complex mixer modified in this way can either be connected to only one output of the polyphase filter or receive a signal which can be obtained by a linear combination of the two output signals of the first polyphase filter 128 arises.

Alternatively, it is possible to use instead of the complex mixer only a purely real mixer having only one input and one output. In such a circuit arrangement, the image rejection is worse than when using a complex mixer, but it can thus be achieved in applications with low image rejection requirement a very simple circuit arrangement.

Furthermore, it is possible to apply to the intermediate frequency amplifier device 148 to waive if it is ensured that the level of the output signals 140 . 142 of the complex mixer 138 is big enough. This has the advantage that the circuit can be further simplified and that the power consumption decreases.

Also the design of the second polyphase filter 158 may vary. Both the use of a bandpass filter and the use of a low pass filter is possible. Thus, the appropriate filter type can be selected, which allows the respective intermediate frequency to pass.

Depending on the location of the intermediate frequency, it is expedient, one of the output signals 160 . 162 of the second polyphase filter or both. If both signals are digitized, then there is an in-phase signal and a quadrature signal in digital form. If only one of the signals is digitized, it is necessary to generate in-phase and quadrature signals digitally. The analog to digital conversion can be done by an analog-to-digital converter or by two analog-to-digital converters. Also in the implementation of two signals, the use of a single converter in time-division multiplex operation is conceivable.

3 shows a block diagram of a polyphase filter with a signal conversion device for use in a frequency converter unit according to the invention. The filtering network is in its entirety with 310 designated. It has one or more signal inputs 312 and one or more signal outputs 314 on. In a preferred embodiment, the filter arrangement comprises a signal conversion device 320 on, the one or more signals from the signal inputs 312 receives and based on two signals to be filtered 330 . 332 generated having a fixed phase relationship to each other. Furthermore, a polyphase filter according to the invention comprises a first filter branch 340 and a second filter branch 342 , which are designed essentially as n-th order low-pass networks. The two filter second 340 . 342 are via a switching network 350 coupled together. At one or more suitable nodes within the first filter branch 340 , the second filter branch 342 or the switching network 350 One or more output signals can be output, which are the signal outputs 314 be supplied.

Starting from the structural description, the operation of a polyphase filter with signal conversion device will be described below. The signal conversion device 320 generated based on an input signal from one of the signal inputs 312 , two signals to be filtered 330 . 332 , which are shifted in their phase against each other. The phase shift may be generated, for example, by a delay line or by a suitable filtering network. For example, this filtering network may be a polyphase filter in which only one signal input is supplied with the input signal while the other signal input is left open. If the polyphase filter is designed for signal conversion, for example as an all-pass filter, it can be achieved that for a given frequency range the output signals have substantially the same amplitude and a predetermined phase relationship. The phase shift between the first signal to be filtered is preferably 330 and the second signal to be filtered 332 about 90 °. The phase shift of 90 ° ensures that the filter arrangement is operated symmetrically with respect to the phase shift. Otherwise, the signals to be filtered correspond to those shifted by 90 ° 330 . 332 an in-phase signal and a quadrature signal, as typically used in complex signal processing.

The two filter branches 314 . 342 are essentially designed as a low-pass filter. This allows realization alone with resistors and capacitors. Inductors, on the other hand, are not necessary. This in turn is very advantageous for an integrated design of a corresponding filter arrangement, since inductances can be realized only with difficulty. As described above, the first filter branch 340 and the second filter branch 342 with signals 330 . 332 operated, which are phase-shifted by 90 °, so also the signals within the filter branches have a phase shift against each other. Will now over the coupling network 350 a signal from the first filter branch 340 to the second filter branch 342 coupled over, so this over-coupled signal has over that in the second filter branch 342 signal present at the coupling-in node has a specific phase shift. The effect of the phase shift is substantially identical to the effect of a phase shift caused by a reactive device in a conventional filter. In particular, by the above-described coupling between two filter branches whose input signals are shifted in phase against each other, the same effects can be achieved using purely resistive coupling elements, as they are achieved in conventional filters by the introduction of additional reactive elements, in particular inductors. Thus arises in interconnections of two low-pass circuits with the previously described coupling network 350 a filter which has a bandpass characteristic with respect to its frequency response. Furthermore, such a filter is also sensitive (or selective) to changes in the phase relationship between the signals to be filtered 330 and 332 ,

Based on the topology described above, it is possible to design polyphase bandpass filters with an order greater than one. Only low-pass filters of the desired order are necessary as filter prototypes.

The above-described circuit arrangement can be varied within a wide range. In particular, it is advantageous to use either one signal input or two signal inputs. The use of a signal input is advantageous when a signal conversion device 320 is used. This is preferably designed to receive an input signal and to provide two phase-shifted signals based thereon. If two input signals are already available, then the signal conversion device can be used 320 completely dispensed with. The polyphase filter without signal conversion device 320 then essentially comprises only two filter branches 340 . 342 having the structure of an n-th order low pass and a coupling network 350 that the two filter branches 340 . 342 coupled with each other.

The output signal may preferably be an output signal from one of the two filter branches 340 . 342 be used. Likewise, for many applications, it is beneficial to use two output signals, each of the output signals being the output of a filter branch 340 . 342 represents. Such an embodiment is favorable, since at the outputs typically already an in-phase and a quadrature signal are available, which can be further processed accordingly in an advantageous manner.

4 shows a detailed block diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention. The polyphase filter is in its entirety with 410 designated. It has an input I _i for an in-phase signal, an input Q _i for a quadrature signal and an output I _o for an in-phase signal and an output Q _o for a quadrature signal.

Furthermore, the polyphase filter comprises 410 a first filter member 420 first order, a second filter member 424 first order, a third filter member 428 first order and a fourth filter member 432 first order. Each filter element essentially has a first-order transfer characteristic, that is, apart from higher-order parasitics. Each filter element receives an input signal intended for the respective filter element and outputs an associated output signal. The first filter member 420 receives an input signal coming from the input I _i for the in-phase signal, depends on the output of the second filter element and on the output of the fourth filter element, the contribution of the respective signals by scalers 440 . 442 . 444 is determined. The second filter element 424 receives its input signal from the output of the first filter element 420 and from the output of the fourth filter member 432 again via scaling facilities 446 . 448 , The input signal of the third filter element is obtained from the signal at the input Q _i for the quadrature signal as well as from the output signal of the second filter element 424 and the fourth filter member 432 formed, wherein the weighting of the individual signals by the scaling 450 . 452 . 454 is determined. The input signal of the fourth filter element 432 is determined by the output signals of the second filter element 424 and the third filter member 428 determined, again scaling 456 . 458 be used. The output signal of the second filter element 424 is provided at the output I _o for the in-phase signal, the output signal of the fourth filter element 432 is provided at the Q _o output for the quadrature signal. For the following description, a first filter branch is still defined, the input I _i for the in-phase signal, the first and the second filter element 420 . 424 , and the output I _o for the in-phase signal and the associated scaling 440 . 442 . 444 . 446 . 448 includes. The second filter branch comprises the input Q _i for the quadrature signal, the third and fourth filter element 428 . 432 , the output Q _o for the quadrature signal and the associated scaling elements 450 . 452 . 454 . 456 . 458 ,

Based on the structural description, the operation of the second-order polyphase filter will be described in more detail below. The second order polyphase filter has two coupled filter branches, one of which processes substantially the in-phase signal and the other essentially processes the quadrature signal. An in-phase signal, which is applied to the input I _i for the in-phase signal, passes through the first filter element 420 and the second filter member 424 in which, depending on the frequency of the signal, a predetermined phase shift between the output signal at the output of the second filter element 424 and the input signal to the in-phase input I _i is formed. The same applies analogously to a signal which is fed to the quadrature input Q _i . With proper operation of the polyphase filter, there is a predetermined phase shift between the input signals at the in-phase input I _i and the quadrature input Q _i . In the present filter structure, the signal at the output of the first filter branch, that is to say at the output of the second filter element, is coupled into the second filter branch and vice versa. Due to the required characteristics of the input signals at the inputs I _i and Q _i , which have a predetermined phase relationship, the signals in outputs of the second and fourth filter elements, which are caused by the respective input signals, also have a predetermined phase relationship. The signals coupled in by the output of the first branch and the second branch thus exhibit a phase shift with respect to the signals generated in the branches. This phase shift corresponds in effect to a phase shift that can be generated by a reactive circuit element. The mutual coupling of the branches, whose input signals are shifted in phase, thus has the same effect as the introduction of further reactive components in the filter circuit. Since the output signals of the filter circuit are essentially determined by resonance effects and thereby essentially by the phase position of the relevant signals, the coupling of the two filter branches can have a serious influence on the filter characteristic. In particular, with a suitable design of the filter members and the scaling members, it is possible, for example, to realize a bandpass filter with a circuit arrangement which only comprises capacitors and resistors. In this case, low-pass filters are used as filter elements of the first order, while the scaling members are realized purely resistively. The corresponding shift of the pass frequency range is effected by the phase-shifted coupling between the two filter branches. The phase shift between the filter branches results in signals being transferred from one filter branch to the other, which could only be generated in the filter branch itself with the aid of inductors.

5 shows a simplified circuit diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention. The polyphase filter is in its entirety with 510 designated. It comprises a first filter branch 512 and a second filter branch 514 , The first filter branch comprises a pair of differential inputs I _i +, I _i - for receiving an in-phase input signal and a pair of differential outputs I _o +, I _o - for outputting an in-phase output signal. Similarly, the second filter branch has a differential input pair Q _i +, Q _i - for receiving a quadrature input signal and a pair of outputs Q _o +, Q _o - for outputting a quadrature output signal. Apart from the names of the inputs and outputs, the two filter branches are constructed analogously, so that essentially only the first filter branch is described here. Furthermore, it should be noted that the two filter branches are constructed symmetrically in themselves, so that they have two mutually symmetrical signal paths. The filter is thus designed for operation with differential signals. This reduces the active and passive sensitivity to interference. Furthermore, the symmetrical design means that all circuit structures are duplicated.

The first filter branch 512 comprises as filter elements a low-pass filter 520 with a capacitor C ₂ and an integrator circuit 524 that a differential operational amplifier 526 and two capacitors C ₁ and can also be understood as a low-pass filter. In each of the two filter branches 512 . 514 a positive signal path is defined describing the signal processing chain between the positive input I _i +, Q _i + and an associated positive output I _o +, Q _o +. A negative signal path characterizes the signal processing chains between the respective negative inputs and outputs. As already explained, there is a symmetry between the positive and the negative signal path. In the following, the positive signal path of the first filter branch 512 described. In particular, it comprises a capacitor C ₂ whose first terminal is connected to the reference potential GND and whose second terminal is connected via a resistor R1 to the positive in-phase input I _i +, via a resistor Rcpl3 to the non-inverting one Output of the differential operational amplifier 530 of the second filter path and via a resistor R2 to the inverting output of the differential operational amplifier 526 of the first filter path 512 is coupled. The second terminal of the capacitor C ₂ in the positive signal path of the first filter branch is further connected via a resistor R3 to the noninverting input of the differential operational amplifier 526 coupled. Furthermore, the non-inverting input of the differential operational amplifier 526 via a resistor Rcpl1 to the noninverting output of the operational amplifier 530 coupled. In addition, the operational amplifier is connected as an integrator, that is, a capacitor C1 is connected between the non-inverting input and the inverting output. The positive in-phase output signal I _o + is applied to the inverting output of the operational amplifier 526 decoupled. Analogously, the negative signal path of the first filter branch 512 constructed, wherein the element values are identical as in the positive signal path. The capacitor C2 of the negative signal path of the first filter branch 512 is here via a resistor Rcpl3 with the inverting output of the operational amplifier 530 connected via a resistor R2 to the non-inverting output of the operational amplifier 526 and also via a resistor R1 to the inverting in-phase input I _i -. The inverting input of the operational amplifier 526 is connected via a further resistor R3 to the capacitor C2 of the negative signal path, as well as via a resistor Rcpl1 to the inverting output of the operational amplifier 530 , Similarly as in the positive signal path, the operational amplifier is also in the negative signal path 526 connected as an integrator, that is, there is a capacitor C1 connected between the inverting input and the non-inverting output. The negative in-phase output I _o - is connected to the non-inverting output of the operational amplifier 526 coupled. It should be emphasized once again that the same reference numerals in resistors and capacitors identify components with the same values, not identical components. Rather, a component is uniquely identified by the reference numeral as well as the filter branch and the signal path (positive or negative) in which it is inserted.

The second filter branch 514 is symmetrical to the first filter branch 512 built, so that is omitted here in detail description. Details are rather the 5 refer to.

The polyphase filter 510 implements a polyphase filter as in the block diagram of FIG 4 is described. The essential extension is that in the case of the polyphase filter 510 a differential circuit design is selected. This doubles the number of signal paths and results in each individual signal being represented by a positive and a negative signal. However, here is the connection between the in 4 shown block diagram of a polyphase filter and the in 5 shown simplified circuit diagram of a polyphase filter are shown. Again, only a first filter branch for the in-phase signal is analyzed. The first low pass filter 520 corresponds to the first filter member 420 , The integrator circuit 524 corresponds to the second filter member 424 , The input signal of the first low-pass filter 520 is determined by the coupling network consisting of the resistors R1, R2 and Rcpl3 as a weighted sum of the in-phase input signal and the output signals of the operational amplifier 526 and 530 which are part of the integrator circuit 524 are formed. The resistors R1, R2 and Rcpl3 correspond to the scaling members 444 . 440 and 444 of in 4 shown block diagram. Similarly, resistors R3 and Rcpl1 correspond to the scaling members 446 respectively. 448 of the basis of 4 shown block diagram. The same applies to the second filter branch 514 , Thus, the circuit is according to 5 an embodiment of a filter structure according to the basis of 4 shown block diagram.

6 shows a detailed circuit diagram of a second-order polyphase filter for use in a frequency converter unit according to the invention. The overall circuit is with 610 designated. It has an unbalanced in-phase input 612 and an unbalanced quadrature input 614 on. Signals of the in-phase input and the quadrature input become matching and coupling networks 620 . 622 fed. They are designed to achieve a suitable impedance matching and possibly a signal attenuation of the input signal. Furthermore, the circuit arrangement comprises balancing stages 630 . 632 which generate symmetrical signals from the unbalanced in-phase and quadrature signals. Symmetrierstufen 630 . 632 essentially comprise an operational amplifier with a balanced output as well as some resistors to determine the transmission characteristics. Furthermore, the polyphase filter comprises 610 a first filter branch 640 , as well as a second filter branch 642 , wherein the two filter branches of their construction substantially identical to those in 5 shown circuit arrangement. Only the polarity of the coupling between the two filter branches is partially changed. The corresponding circuit details are the 6 refer to. Further includes the polyphase filter 610 two more decoupling stages 650 . 652 that suppress a DC component in the output signals and make an impedance matching. Furthermore, the circuit arrangement comprises several Blocking and coupling networks 660 . 662 . 664 . 666 . 668 and 670 which suppress disturbances on the operating voltages of the circuit arrangement. There is also an entrance 680 for setting an offset voltage for the differential operational amplifier, the one filter arrangement 682 is downstream.

The operation of the two filter branches 640 . 642 is essentially the same as that of 5 described circuit arrangement. Differential input signals are in balancing stages 630 . 632 generated, and the output signal is through decoupling stages 650 . 652 coupled in differential form, wherein a DC component is suppressed. The present symmetrical circuit arrangement offers the advantage that there is a high flexibility with respect to the phase of the coupled signals, since all signals are present in both inverted and non-inverted form. Furthermore, a symmetrical circuit design is less sensitive to the coupling and decoupling of interference. Finally, in integrated circuits in particular, it is sometimes easier to route differential signal lines than impedance-matched single-ended signal lines.

The circuit described above can be varied within a wide range. In particular, it is not absolutely necessary to choose a differential circuit design. If the phase positions of the signals for the coupling of the two filter branches are already suitable for a simple circuit design, then a differential design is no longer necessary. Thus, at low frequency, cheaper devices (eg, conventional output operational amplifiers rather than differential outputs) can be used, and power consumption can be reduced. Also, a large number of components is saved, which significantly reduces the space requirement and the total cost of production.

The type of feedback and the cross-coupling between the two filter branches can also vary. Here, a coupling by means of resistive components (resistors) is shown. However, other circuit components suitable for coupling may equally well be used, such as transformers, gyrators, operational amplifier circuits, and others. This freedom brings the great advantage that each of the elements can be used for coupling, which are easy to make in a given technology.

Furthermore, different embodiments of a higher-order polyphase filter are possible. In particular, the polyphase filter can be realized passively, that is, without the use of active elements such. B. an operational amplifier. This is advantageous if, due to the very high frequencies to be processed, active components are no longer available. In a passive realization form two possibilities can be distinguished. On the one hand, a realization with concentrated elements is possible. This is useful if either the frequencies to be processed are sufficiently low or if the polyphase filter is produced at higher frequencies on a substrate in an integrated form. The use of passive lumped elements has the advantage that filter design can be done using conventional methods of circuit analysis or synthesis. On the other hand, in particular in the presence of very high frequencies, a distributed design of a polyphase filter may be advantageous. Here, the polyphase filter is realized by means of waveguide and resonator structures, the dimensions of the overall structure being of the order of magnitude of the wavelength or above. Such a realization is usually associated with very low losses and can be realized up to the highest frequencies in the millimeter wave range inside.

Furthermore, it is possible to increase the filter order. For this purpose, further filter stages (comprising the filter elements) are added, and further feedback paths are established. At maximum feedback, feedback networks exist from each output node of a branch to each input node of a second branch. However, the principal structure comprising two branches is retained. The corresponding coupling coefficients can be determined by analytical circuit analysis. It is also possible to set the transmission curve of the filter arrangement by numerical simulative optimization according to a target specification.

Moreover, it is possible to implement all the above-described arrangements not only in terms of hardware, but also in whole or in part in software. This is useful if the frequencies to be processed are low enough to allow digital signal processing. A software implementation brings with it the great advantage that the filter and Frequenzumsetzeranordnungen can be realized without additional hardware complexity by means of a signal processor and that if necessary, the parameters of the arrangement can be changed with minimal effort.

The present invention thus provides a frequency converter unit which can be used in conjunction with information and telecommunications systems in which signals must be selected and / or transferred to another frequency range. This is used in many fields of information or telecommunications, for example in wireless telemetry applications, in mobile phones and in wireless data transmission and other applications. The present invention enables the implementation of a telecommunications signal from one frequency layer to another through a novel network topology. The system features are simultaneously enhanced by a new network topology and the application of novel filtering networks for signal selection. With the new topology involving a polyphase filter upstream of a complex mixer, image frequency rejection in low intermediate frequency architectures using commercial components of about 35 dB achievable with conventional structures can be increased above 50 dB. In addition, the characteristics of frequency selection can be improved by using new filtering networks. Conventionally, when only first-order polyphase filters are used, better edge slope is achieved through the use of a higher-order coupled filter network, and fewer components are required over the use of multiple series-connected first-order polyphase filters. In addition, there are more degrees of freedom in choosing poles and zeros, allowing for further improvement in filter characteristics.

A circuit topology according to the invention is necessary because the use of a conventional, commercial I / Q demodulator or I / Q modulator restricts the achievable system properties. For example, the image frequency selection on the low frequency side of the complex mixer is limited by imperfections such as asymmetries and phase shifts. In the present invention, a novel topology having a higher order filtering network is used on both the high frequency side of an I / Q demodulator / mixer and the low frequency side. This achieves an improvement of important system parameters, for example an increase in the suppression of the image frequency range and the adjacent channels.

The application of a circuit topology according to the invention is not limited to I / Q demodulators, but can also be used in I / Q modulators, z. B. in the generation of signals. In addition to the topology according to the invention, a novel polyphase filter structure is additionally used, which improves the edge steepness of the filter networks used compared to conventional filters (standard filter techniques, first-order polyphase filters). For this purpose, a conventional arrangement of a first-order polyphase structure is modified so that a filter network of higher order with significantly improved properties can be realized by the choice of suitable coupling between certain circuit elements and with a low overhead of components. This higher-order filtering network offers a great deal more degrees of freedom in a design. For example, better filter characteristics can be achieved by a suitable choice of poles and zeros.

In addition, by arranging multiple filter networks with different frequency ranges to a filter bank, the bank width of the system can be increased. This makes it possible, for example, to realize an input part for a shortwave receiver whose frequency range extends from 1 MHz to 30 MHz. The image rejection can be greater than 50 dB.

Also disclosed is a higher order polyphase filter having the following features:
a first signal input and a second signal input for receiving a first input signal and a second input signal; and
a first-order first-order filter element, a first-order second-order filter element, a first-order third-order filter element and a first-order fourth filter element;
wherein an input signal of the first filter element is dependent on the first input signal, an output signal of the second filter element and an output signal of the fourth filter element;
wherein an input signal of the third filter element depends on the second input signal, on the output signal of the second filter element and on the output signal of the fourth filter element;
wherein an input signal of the second filter element depends on an output signal of the first filter element and on the output signal of the fourth filter element;
wherein an input signal of the fourth filter element depends on an output signal of the third filter element and on the output signal of the second filter element; and
wherein the polyphase filter is configured to generate a polyphase filter output in response to a frequency and an amplitude of the first input signal and the second input signal and in dependence on a phase relationship between the first input signal and the second input signal.

Claims (23)

Frequency converter unit comprising: a first polyphase filter having a first input and a second input and a An output, wherein the first polyphase filter is adapted to generate at its output a filtered signal in response to an amplitude, a frequency and a phase relationship of signals applied to its first and second input; a frequency converter having a frequency converter input coupled to the output of the first polyphase filter and a first frequency converter output and a second frequency converter output, the frequency converter means being adapted to provide signals having a signal component based on the signal at the frequency converter input at the first frequency converter output and the second frequency converter output which are shifted in frequency from the signal at the frequency converter input; and a second polyphase filter having a first input coupled to the first frequency converter output and a second input coupled to the second frequency converter output and an output, wherein the second polyphase filter is configured to operate in response to an amplitude, a frequency and a phase relationship of signals applied to its first and second inputs to produce an output signal at its output, wherein the first polyphase filter and the second polyphase filter are configured to individually or in combination desired Nutzfrequenzsignale that at a frequency conversion in the Frequenzumsetzereinrichtung to a predetermined frequency interval be formed to transmit from the first and second input of the first polyphase filter to the output of the second polyphase filter, and unwanted image frequency signals, which in the frequency conversion in the frequency converter to the predetermined Fr the first or second polyphase filter is a higher order polyphase filter having: a first signal input and a second signal input for receiving a first input signal and a second input signal; a first-order first-order filter element, a first-order second-order filter element, a first-order third-order filter element and a first-order fourth filter element; and wherein an input signal of the first filter element is dependent on the first input signal, an output signal of the second filter element and an output signal of the fourth filter element; wherein an input signal of the third filter element depends on the second input signal, on the output signal of the second filter element and on the output signal of the fourth filter element; wherein an input signal of the second filter element depends on an output signal of the first filter element and on the output signal of the fourth filter element; wherein an input signal of the fourth filter element depends on an output signal of the third filter element and on the output signal of the second filter element; and wherein the polyphase filter is configured to generate a polyphase filter output signal in response to a frequency and an amplitude of the first input signal and the second input signal, and in dependence on a phase relationship between the first input signal and the second input signal. The frequency converter unit of claim 1, wherein the first polyphase filter further comprises a second output, wherein the first polyphase filter is configured to receive signals filtered at its first output and its second output in response to an amplitude, a frequency, and a phase relationship at its first and second outputs generate second input applied signals; and wherein the frequency converter means further comprises a second frequency converter input coupled to the second output of the first polyphase filter, the frequency converter means being arranged to provide signals at one of the first frequency converter input and the second frequency converter input at the first frequency converter output and the second frequency converter output Provide signal component which are shifted relative to the signals at the first frequency converter input and the second frequency converter input with respect to a frequency. Frequency converter unit according to claim 1 or 2, wherein the first polyphase filter is preceded by a Signalkonvertierungseinrichtung which is adapted to receive an input signal and due to its two phase shifted with respect to each other shifted signals to the first input and the second input of the first polyphase filter available , A frequency converter unit according to claim 3, wherein the signal converting means comprises a phase shifter configured to generate a phase shifter output delayed by a predetermined delay time in response to a phase shifter input signal. Frequency converter unit according to claim 4, wherein the delay time is variable predetermined. Frequency converter unit according to claim 3, wherein the signal converting means comprises a third polyphase filter having an input and a first output and a second output configured to output signals having a predetermined phase relationship to each other based on a signal at an input at its first output and at its second output. A frequency converter unit according to claim 6, wherein the third polyphase filter has an allpass characteristic designed such that an amplitude of the signals at its first output and its second output within a predetermined tolerance range are equal and independent of a frequency of the signal at its input. Frequency converter unit according to claim 7, wherein the tolerance range is ± 3 dB. Frequency converter unit according to one of claims 1 to 8, wherein the first polyphase filter is a bandpass filter. A frequency converter unit according to any one of claims 1 to 9, wherein the first polyphase filter is an active filter comprising active devices configured to amplify an electrical signal. A frequency converter unit according to claim 10, wherein the first polyphase filter comprises an operational amplifier. A polyphase filter according to any one of claims 1 to 9, wherein the first polyphase filter is a passive filter. Frequency converter unit according to one of claims 1 to 12, wherein the first polyphase filter comprises a filter bank with a plurality of individual filters, which can be switched by a switching device optionally between the inputs and the outputs of the first polyphase filter. Frequency converter unit according to one of claims 1 to 13, wherein the first polyphase filter comprises a wideband bandpass filter whose bandwidth is greater than the center frequency. Frequency converter unit according to one of claims 1 to 14, wherein the first polyphase filter has a filter order which is at least equal to 2 and / or in which the second polyphase filter has a filter order which is at least equal to 2. A frequency converter unit according to any one of claims 1 to 15, wherein the frequency converter means comprises a complex mixer adapted to receive an input signal from the first frequency converter input and to provide two phase-shifted signal components at the first frequency converter output and the second frequency converter output , The frequency converter unit of claim 16, wherein the complex mixer comprises a first and a second single mixer, the first single mixer adapted to receive an input signal from the first frequency converter input and a first local oscillator signal and to provide a signal at the first frequency converter output based on these signals. and wherein the second single mixer is configured to receive an input signal from the first frequency converter input and a second local oscillator signal phase shifted from the first local oscillator signal, and to provide a signal at the second frequency converter output based on these signals. A frequency converter unit according to claim 2, wherein the frequency converter means comprises a first mixer adapted to receive an input signal from the first frequency converter input and a first local oscillator signal and thereby provide a signal at the first frequency converter output, and a second mixer adapted to to receive an input signal from the second frequency converter input as well as a second local oscillator signal and thereby provide a signal at the second frequency converter output. Frequency converter unit according to claim 18, wherein the first local oscillator signal with respect to a phase position equal to the second local oscillator signal. Frequency converter unit according to claim 18, wherein the first local oscillator signal is shifted relative to the second local oscillator signal with respect to a phase position. A frequency converter unit according to claim 2, wherein said frequency converter means comprises a complex mixer adapted to receive signals from said first and second frequency converter inputs, and a first local oscillator signal and a second local oscillator signal shifted in phase with respect to said first local oscillator signal, and based thereon on the first frequency converter output and the second frequency converter output, to provide signals having a signal component which are shifted in frequency from the signals at the first frequency converter input and the second frequency converter input. Frequency converter unit according to claim 21, wherein the complex mixer comprises a first, second, third and fourth mixers, wherein inputs of the first and second mixers are coupled to the first frequency converter input, wherein inputs of the third and fourth mixers are coupled to the second frequency converter input, the first and third mixers being coupled to the first local oscillator signal, the second and fourth mixers are coupled to the second local oscillator signal and wherein the signal at the first frequency converter output is formed by a combination of output signals of the first and fourth mixers and wherein the signal at the second frequency converter output is formed by combining output signals of the second and third mixers. Polyphase filter with the following features: a first signal input and a second signal input for receiving a first input signal and a second input signal; and a first-order first-order filter element, a first-order second-order filter element, a first-order third-order filter element and a first-order fourth filter element; wherein an input signal of the first filter element is dependent on the first input signal, an output signal of the second filter element and an output signal of the fourth filter element; wherein an input signal of the third filter element depends on the second input signal, on the output signal of the second filter element and on the output signal of the fourth filter element; wherein an input signal of the second filter element depends on an output signal of the first filter element and on the output signal of the fourth filter element; wherein an input signal of the fourth filter element depends on an output signal of the third filter element and on the output signal of the second filter element; and wherein the polyphase filter is configured to generate a polyphase filter output in response to a frequency and an amplitude of the first input signal and the second input signal and in dependence on a phase relationship between the first input signal and the second input signal.

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