KR100749804B1 - Direct Conversion Transmit System using Optimized CFL - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

The present invention relates to a gain control apparatus for a super narrowband transmission system using a Cartesian feedback loop.

2. The technical problem to be solved by the invention

According to the present invention, in a direct conversion ultra narrowband transmission system using a Cartesian Feedback Loop (CFL), an I / Q variable attenuator for phase shifter and open loop gain control is located in a baseband region rather than an RF frequency region. When controlling the transmit power, DSP (Digital Signal Processor) is used to adjust the gain of the open loop and the attenuation of the closed loop together to adjust the phase and gain without being affected by the transmit output frequency and transmit without deteriorating the stability of the CFL loop. An object of the present invention is to provide a gain control device of a ultra narrowband transmission system using a Cartesian feedback loop for controlling power.

3. Summary of Solution to Invention

In the gain control apparatus of a transmission system using a Cartesian feedback loop, the present invention processes transmission data to output baseband transmission I / Q (In phase / Quadrature phase) channel signals, and demodulates the I / Q demodulation means. Digital signal processing means for controlling phase adjustment in the phase shifting means, I / Q variable attenuation means, and scaling in the I / Q demodulation means in accordance with a baseband transmit I / Q channel signal; I / Q demodulation means for demodulating a transmission high frequency signal output from the transmission means into a baseband transmission I / Q channel signal; I / Q error amplifying means for amplifying a distortion signal by comparing a baseband transmit I / Q channel signal demodulated by said I / Q demodulation means with a baseband transmit I / Q channel signal output from said digital signal processing means; The phase shifting means for inverting the phase of the distortion signal amplified by the I / Q error amplifying means in a baseband region; The I / Q variable attenuation means for adjusting the magnitude of the distortion signal inverted by the phase shifting means in a baseband region; And said transmitting means for modulating a baseband transmit I / Q channel signal comprising a distortion signal with an inverted and scaled amplitude from said I / Q variable attenuation means into a transmit high frequency signal.

4. Important uses of the invention

The present invention is used for gain control of ultra narrowband transmission system.

Cartesian Feedback Loop, Gain Control, Baseband Domain, I / Q Variable Attenuator

Description

Gain Control Device for Ultra Narrowband Transmission System Using Cartesian Feedback Loop {Direct Conversion Transmit System using Optimized CFL}

1 is a block diagram of a gain control apparatus of a super narrowband transmission system using a conventional Cartesian feedback loop;

2 is a configuration diagram of a gain control apparatus of a ultra narrowband transmission system using a Cartesian feedback loop according to the present invention;

3 is an exemplary view illustrating a correlation between an ideal output power and an attenuation amount according to the present invention.

* Explanation of symbols for the main parts of the drawings

201: Digital signal processor 202: I error amplifier

203: Q error amplifier 204: Phase shifter

205: I variable attenuator 206: Q variable attenuator

207: I modulator 208: Q modulator

209: 90 degree phase shifter 210: Local oscillator

211: I / Q combiner 212: power amplifier

213: directional coupler 214: variable attenuator

215: power divider 216: Q demodulator

217: I demodulator 218: power detector

219: phase shifter control signal 220: I / Q variable attenuator control signal

221: variable attenuator control signal

The present invention relates to a gain control apparatus for a super narrowband transmission system using a Cartesian feedback loop, and more particularly, for phase shifter and open loop gain control in a super narrowband transmission system using a direct conversion scheme using a Cartesian feedback loop (CFL). Transmit by positioning the I / Q variable attenuator in the baseband region instead of the RF (Radio Frequency) frequency domain and controlling the gain of the open loop and the attenuation of the closed loop by using a digital signal processor (DSP) when controlling the transmit power. A gain control apparatus of a ultra narrowband transmission system using a Cartesian feedback loop for controlling phase and gain without being affected by an output frequency and controlling transmission power without deteriorating stability of a CFL loop.

Current communication systems have evolved to transmit more information in narrower frequency bands. To this end, digital modulation is the mainstream.

Radios used for simple radio stations have also been actively studied for ultra narrowband (6.25KHz) digital transmission.

However, the ultra narrowband digital modulation scheme uses a quadrature phase shift keying (QPSK) modulation scheme compared to the conventional FM scheme, so that the ratio of the maximum power and the average power of the transmission signal is 10 dB or more. For this reason, in order to transmit a signal without distortion of the signal, the transmit power amplifier in front of the antenna must use a power amplifier larger than the desired power.

To alleviate this drawback, a method of reducing the maximum power of the power amplifier and reducing the distortion of the signal by using an additional linearization circuit is generally used.

The linearization method using a Cartesian feedback loop (CFL) is one of them, and is a linearization method used in a communication system in which a communication band is narrow and relatively low in phase distortion caused by feedback.

This CFL linearization method modulates a baseband signal, amplifies the modulated signal in a power amplifier, extracts the amplified signal using a directional coupler, and then demodulates the signal to demodulate the base before modulation. It is a method of improving the distortion of a signal by forming a feedback circuit coupled with a band signal.

In order to improve the linearity, it is necessary to determine the magnitude and phase of the signal to change the magnitude and phase of the demodulated signal to find and operate the optimum point. The attenuation of the gain and feedback loops must be adjusted.

In addition, in the case of a CFL applied system, when a closed loop is formed, the gain is not determined by the gain of the open loop but by the amount of attenuation of the attenuator present in the feedback loop. At this time, when trying to adjust the output power of the transmitter inserted into the CFL, if only the attenuation amount of the attenuator is adjusted, the overall loop gain increases and stability decreases.

1 is a block diagram of a gain control apparatus of a conventional narrowband transmission system using a Cartesian feedback loop.

The information signal generated in the baseband passes through the I / Q modulators 103 and 109 and combines with the signal generated by the local oscillator 111 to achieve frequency modulation.

Thereafter, the power amplifier 105 is amplified and radiated through the antenna. At this time, the directional coupler 106 is inserted into the end of the power amplifier 105 to extract the radiated information signal, passes through the variable attenuator 113, attenuates the signal value of the desired power level, and then again the I / Q demodulator. Demodulate the signal into baseband signals using (114, 116). Here, the demodulated signal includes information on the distortion component generated while passing through the power amplifier 105.

The demodulated signal is applied to the I / Q error amplifiers 102 and 110 again, and the information signal, the power amplifier 105 and the feedback circuit applied from the first baseband are applied to the I / Q error amplifiers 102 and 110. By comparing the distortion signal generated during the process, the phase of the distortion signal is reversed, so that the output of the error amplifier forms a signal including the predistortion signal.

When the pre-distorted signal is applied to the power amplifier 105, the signal is canceled from the distortion component generated by the power amplifier 105, so that the power amplifier 105 has a linear operation.

As described above, in order to make the line distortion component, it is necessary to optimize the attenuation value and the phase change value of the variable attenuator 113 and the phase shifter 107. In order to adjust the variable attenuator 113 and the phase shifter 107, the phase control signal P1 and the magnitude control signal M1 are converted into the phase shifter 107 and the variable attenuator in the digital signal processor (DSP) 101. 113).

The gain control apparatus of the conventional narrow-band transmission system using the Cartesian feedback loop uses the output of the local oscillator 111, between the open loop I / Q modulators 103 and 109 and the local oscillator 111. FIG. A phase shifter 107 was applied to the path of to adjust the phase difference between the open loop input signal and the signal coming through the feedback loop. That is, the phase difference between the open loop I / Q modulators 103 and 109 and the feedback loop I / Q demodulators 114 and 116 were adjusted.

Therefore, as the frequency of the local oscillator increases, the time of one cycle decreases, and it is very difficult to implement the actual phase shifter, and thus there is a disadvantage that a high performance device must be used. In other words, if the output frequency of the local oscillator is 1 GHz, one clock is 1 ns, and to adjust the phase in 11.25 degree intervals, the waveform of 1/32 ns needs to be controlled.

In addition, when the output power is adjusted, only the gain is adjusted by adjusting the attenuation value of the variable attenuator of the feedback loop, which affects the overall loop gain and thus adversely affects the stability of the loop and even oscillates.

The present invention has been proposed to solve the above problems, and the phase shifter and I / Q variable attenuator for open loop gain control in a direct conversion type ultra narrowband transmission system using a Cartesian Feedback Loop (CFL) is a radio frequency (RF) frequency. It is located in the baseband region, not in the region, and by adjusting the gain of the open loop and the attenuation of the closed loop by using a digital signal processor (DSP) to control the transmit power, the phase and gain are controlled without being affected by the transmit output frequency. In addition, an object of the present invention is to provide a gain control device of a ultra narrowband transmission system using a Cartesian feedback loop for controlling transmission power without deteriorating stability of a CFL loop.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

An apparatus of the present invention for achieving the above object, in the gain control apparatus of the transmission system using a Cartesian feedback loop, processing the transmission data to output a baseband transmission I / Q (In phase / Quadrature phase) channel signal Digital for controlling the phase adjustment in the phase shifting means and the I / Q variable attenuation means and the size adjustment in the I / Q demodulation means according to the baseband transmit I / Q channel signal demodulated by the I / Q demodulation means. Signal processing means; I / Q demodulation means for demodulating a transmission high frequency signal output from the transmission means into a baseband transmission I / Q channel signal; I / Q error amplifying means for amplifying a distortion signal by comparing a baseband transmit I / Q channel signal demodulated by said I / Q demodulation means with a baseband transmit I / Q channel signal output from said digital signal processing means; The phase shifting means for inverting the phase of the distortion signal amplified by the I / Q error amplifying means in a baseband region; The I / Q variable attenuation means for adjusting the magnitude of the distortion signal inverted by the phase shifting means in a baseband region; And said transmission means for modulating a baseband transmission I / Q channel signal including a distortion signal of which the inversion and amplitude of said I / Q variable attenuation means are adjusted to a transmission high frequency signal.

In addition, the present invention implements the phase shift of the CFL in the baseband when using the CFL linearization method to change the phase difference between the open loop path and the feedback loop path irrespective of the output frequency, thereby enabling proper CFL operation and change the output power By appropriately adjusting the open loop gain of the CFL and the attenuation of the feedback loop, the entire closed loop always operates at steady state.

In addition, when the respective output power is determined, the present invention expresses the relationship between the optimum open loop gain and the feedback loop attenuation for the output power as a function, and adjusts the control signal using the DSP.

In addition, the present invention facilitates the adjustment of the signal by performing the phase shift of the feedback circuit for linearity improvement after demodulating the baseband signal, that is, the high frequency caused by the control of the phase of the existing local oscillator signal, that is, high frequency. The error component increases in the control of the ground local oscillator signal, which eliminates the disadvantage of degrading the operation of the entire CFL.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram of a gain control device of a ultra narrowband transmission system using a Cartesian feedback loop according to the present invention, and illustrates a CFL circuit for controlling phase and output power in a baseband.

As shown in FIG. 2, a gain control apparatus of a ultra narrowband transmission system using a Cartesian feedback loop according to the present invention processes a transmission data to output a baseband transmission I / Q channel signal, and an I / Q demodulation unit. Phase adjustment in the phase shifter 204 and size adjustment in the I / Q variable attenuators 205 and 206 and the I / Q demodulator 21 according to the baseband transmit I / Q channel signal demodulated in (21). Part of the digital signal processor 201 and the Cartesian feedback loop (CFL) for controlling a signal, and for demodulating the transmission high frequency signal output from the direct conversion transmitter 20 into a baseband transmission I / Q channel signal. The baseband transmit I / Q channel signal demodulated by the / Q demodulator 21 and the I / Q demodulator 21 and the baseband transmit I / Q channel signal output from the digital signal processor 201, I / Q error amplifiers 202 and 203 for amplifying distortion signals, A phase shifter 204 for inverting the phase of the distortion signal amplified by the I / Q error amplifiers 202 and 203 in the baseband region, and a phase shifter 204 of the distortion signal inverted by the phase shifter 204 in the baseband region. A baseband transmit I / Q channel signal comprising an I / Q variable attenuator 205, 206 for adjusting the magnitude, and an inverted and scaled distortion signal output from the I / Q variable attenuator 205, 206. It includes a direct conversion transmitter 20 for modulating the transmission into a high frequency signal by using a direct conversion method.

In more detail, the direct conversion transmitter 20 modulates the baseband transmission I / Q channel signal output from the digital signal processor 201 into a transmission high frequency signal using a direct conversion scheme. The grandfather 21 is a part of the Cartesian feedback loop (CFL), which demodulates the transmission high frequency signal output from the direct conversion transmitter 20 into a baseband I / Q channel signal and delivers it to the digital signal processor 201. Perform the function.

The baseband transmit I / Q channel signal generated by the digital signal processor (DSP) 201 is compared with the feedback signal applied through the feedback loop while passing through the I error amplifier 202 and the Q error amplifier 203 and is differential. This amplified signal (distorted signal) is phase shifted and scaled in the baseband region via phase shifter 204 and I / Q variable attenuators 205 and 206.

The phase shifted and scaled distortion signal is frequency-modulated through the I modulator 207 and the Q modulator 208, and the modulated signal is added via the power combiner 211, and again the power amplifier. Amplified through 213.

The amplified signal is extracted through the directional coupler 213 and then demodulated back to the baseband signal while passing through the variable attenuator 214, the I demodulator 217, and the Q demodulator 216.

The demodulated signal includes the distortion component generated while passing through the power amplifier 212.

The signal thus produced and the first baseband transmit I / Q channel signal produced by the DSP 201 are applied together to the error amplifiers 202 and 203 to generate a distortion signal. The linearity of the power amplifier 212 is improved by applying the signal thus produced to the power amplifier 212.

On the other hand, the attenuation amount of the variable attenuators 205 and 206 for gain control of the open loop, the attenuation amount of the variable attenuator 214 of the feedback loop, and the output power have a constant correlation. That is, the attenuation amount of the feedback loop variable attenuator 214 and the attenuation amount of the open loop gain control variable attenuators 205 and 206 according to the change of the output power are detected and expressed as a function as shown in Equation 1 below.

         Y = a * X1 + b

         X1 = F (X2)

Here, Y is an output power, X1 is an attenuation amount of the feedback loop variable attenuator 214, X2 is an attenuation amount of the open loop gain control variable attenuators 205 and 206, and F () is a function representing the relationship between X1 and X2. In this case, Y is a linear function having an initial value b (constant) and a variation a (constant).

When the output power, the attenuation amount of the feedback loop variable attenuator 214, and the attenuation amount of the variable attenuators 205 and 206 for open loop gain control are expressed as a function, when a desired output power is to be controlled, Once determined, the output power is controlled by DSP operation (determined X1 by Equation 1), not by lookup table, and the open loop gain is adjusted to maintain the loop gain stability of the entire system. Adjust

3 is an example showing the correlation between the ideal output power according to the present invention, the amount of attenuation of the feedback loop variable attenuator 214, and the amount of attenuation of the variable attenuators 205 and 206 for open-loop gain adjustment.

The present invention provides a phase shifter 204 with an I / Q error amplifier 202 and 203 and an I / Q variable attenuator to change the phase difference between the open loop and the feedback loop. (205, 206). In this case, the phase shifter 204 is located in the baseband (baseband) region, so that the phase shifter 204 is placed in a local oscillator, which is a conventional radio frequency (RF) frequency region, so that it is easier to adjust the signal processing than to process the RF region. .

In addition, the present invention is easier than adjusting the gain in the RF domain by placing the I / Q variable attenuators 205 and 206 for adjusting the open loop gain in the baseband region to adjust the gain.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

In the present invention as described above, the phase shifter and the open loop gain control I / Q variable attenuator in a direct conversion type ultra narrow band transmission system using a Cartesian Feedback Loop (CFL) is not a baseband region but an RF frequency region. The digital signal processor (DSP) controls the gain of the open loop and the attenuation of the closed loop to control the phase and gain without affecting the transmission output frequency, and the stability of the CFL loop. There is an effect that can control the transmission power without deterioration.

In addition, in the direct conversion ultra narrowband transmission system using a Cartesian Feedback Loop (CFL), the present invention provides a phase shifter and an I / Q variable attenuator for open-loop gain control in a baseband region rather than a radio frequency (RF) frequency domain. By doing so, it is possible to avoid the difficulty of implementing the phase shifter and the variable attenuator for adjusting the open loop gain in the existing RF domain, and to reduce the burden of redesigning the phase shifter or the variable attenuator for the output frequency even if the output frequency changes. There is.

In addition, the present invention expresses the correlation between the feedback loop attenuation and the opening gain as a function to adjust the output power of the ultra narrowband transmission system as a function and uses the operation of the DSP to look up a table for each system. You can avoid the hassle of setting up each action by creating a table).

Claims (2)

In the gain control apparatus of the transmission system using a Cartesian feedback loop, Outputs a baseband transmit I / Q channel signal by processing the transmission data, and adjusts the phase in the phase shifting means according to the baseband transmit I / Q channel signal demodulated by the I / Q demodulation means. Digital signal processing means for controlling scaling in the I / Q variable attenuation means and in the I / Q demodulation means; I / Q demodulation means for demodulating a transmission high frequency signal output from the transmission means into a baseband transmission I / Q channel signal; I / Q error amplifying means for amplifying a distortion signal by comparing a baseband transmit I / Q channel signal demodulated by said I / Q demodulation means with a baseband transmit I / Q channel signal output from said digital signal processing means; The phase shifting means for inverting the phase of the distortion signal amplified by the I / Q error amplifying means in a baseband region; The I / Q variable attenuation means for adjusting the magnitude of the distortion signal inverted by the phase shifting means in a baseband region; And The transmission means for modulating a baseband transmission I / Q channel signal including a distortion signal of which the inversion and amplitude of the I / Q variable attenuation means are adjusted; Gain control device of a super narrowband transmission system using a Cartesian feedback loop comprising a. The method of claim 1, The digital signal processing means, For output power, gain is controlled through Equation A below, which represents a correlation between the attenuation of the I / Q variable attenuation means, the attenuation of the variable attenuator in the I / Q demodulation means of the feedback loop, and the output power. Gain control device of a super narrowband transmission system using a Cartesian feedback loop, characterized in that. Equation A  Y = a * X1 + b  X1 = F (X2) Here, Y is an output power, X1 is an attenuation amount of the feedback loop variable attenuator 214, X2 is an attenuation amount of the open loop gain control variable attenuators 205 and 206, and F () is a function indicating the relationship between X1 and X2. . In this case, Y is a linear function having an initial value b (constant) and a variation a (constant).

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