JP3984377B2 - Digital modulator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication apparatus, and more particularly to a digital modulation apparatus used for a digital transmitter.
[0002]
[Background Art and Problems to be Solved by the Invention]
In general, a digital transmitter uses a digital modulation device to convert a baseband signal represented by binary information into an analog RF transmission signal. Some digital modulation devices use a polar loop, a Cartesian loop, or the like, and an IQ modulation device (orthogonal modulation device) is used in any of the methods. In the IQ modulation apparatus, it is necessary to accurately maintain the 90-degree phase difference and gain between the in-phase component (I) and the quadrature component (Q). Otherwise, carrier leak and image frequency will occur. For this reason, various attempts to compensate for the phase difference and the gain have been made, but there is a demerit that the circuit scale is large and complicated. An object of the present invention is to provide a digital modulation device that does not use an IQ modulation device. Furthermore, an object of the present invention is to simplify the circuit configuration.
[0003]
[Means for Solving the Problems]
The above-described problem is solved by the digital modulation device (100) that generates the RF transmission signal based on the envelope input signal (102) representing the amplitude of the transmission signal and the phase data (104) representing the phase of the transmission signal. The digital modulation device (100) has a frequency equal to the frequency of the RF transmission signal and outputs a constant amplitude signal having a constant amplitude. The limiter (106), the phase data (104) and the RF transmission frequency based on the constant amplitude signal A transmission frequency setting unit (108) for generating (fo), difference signal generating means (110) for generating a difference signal between the envelope signal extracted from the RF transmission signal and the envelope input signal (102), and the RF transmission frequency (Fo) and an amplification stage (120) for generating an RF transmission signal based on the difference signal. The transmission frequency setter (108) receives the signal from the frequency divider (1082) that receives the phase data (104) and the constant amplitude signal, and the frequency divider (1082) filtered by the filter (1084), A voltage controlled oscillator (1086) that outputs a signal having an RF transmission frequency is formed.
[0004]
【Example】
FIG. 1 is a block diagram illustrating a digital modulator (100) according to the present invention. The antenna (130) is coupled to the first terminal of the attenuator (122) via a directional coupler. The second terminal of the attenuator (122) is coupled to the input of the limiter (106). The output of the limiter (106) is coupled to a first input terminal of a fractional frequency divider (1082) having first and second input terminals, and the second input terminal receives phase data (104) which is a digital signal. . The output of the fractional divider (1082) is coupled to the input of a phase detector (PD) that is coupled to the local oscillator (1081). The output of the phase detector PD (1083) is input to the Nyquist filter (1084). The output of the Nyquist filter (1084) is coupled to the input of a voltage controlled oscillator VCO (1086).
[0005]
On the other hand, the envelope input signal (102) is an analog signal corresponding to the amplitude component of the signal to be transmitted, and is coupled to the first input of the operational amplifier (1104). The first input of the mixer (1102) is coupled to the input of the limiter (106), the second input is coupled to the output of the limiter (106), and the output of the mixer (1102) is coupled to the second input of the operational amplifier (1104). Is done.
[0006]
Next, the first input of the modulation amplifier (1202) having the first and second inputs is coupled to the output of the voltage controlled oscillator (1086) and the second input is coupled to the output of the operational amplifier (1104). The input of the power amplifier (1204) is coupled to the output of the modulation amplifier (1202), and the output of the power amplifier (1204) is coupled to the antenna (130).
[0007]
FIG. 2 shows a block diagram for generating an envelope input signal (102) and phase data (104). In FIG. 2, operations such as mapping and Nyquist filters are performed using a DSP, but the present invention is not limited to this. When the DSP is used, the circuit configuration is simplified as compared with the case where individual discrete elements are used. Hereinafter, a case where the modulation method is π / 4QPSK will be described as an example. The serial data shown on the left side in the figure is converted into a 2-bit signal (symbol) and mapped to a corresponding position on the signal constellation. Next, polar coordinate conversion is performed based on the mapped position (coordinates). Polarization is performed by calculating the magnitude (Mag) and phase (θ) of the amplitude based on the in-phase and quadrature components of the signal. A signal representing the magnitude of the amplitude is converted into an analog signal through a Nyquist filter, and becomes amplitude data (102). (Θ) representing the phase is differentiated and converted into frequency data, which becomes phase data (104).
[0008]
The operation will be described next.
[0009]
For example, the envelope input signal (102) and the phase data (104) are given signals representing the amplitude and phase of the π / 4QPSK signal. The phase signal is a digital signal having a symbol rate of 4800 baud, for example, and is input to the transmission frequency setter (108). On the other hand, the RF transmission signal is input to the limiter (106) via the attenuator (122). The constant amplitude signal output from the limiter (106) is a signal having an RF transmission frequency substantially equal to the frequency of the RF transmission signal and having a constant amplitude. The transmission frequency setter (108) operates to lock up to the RF transmission frequency (fo) using the constant amplitude signal and the phase data (104). That is, after multiplying the frequency obtained from the local oscillator (1081) by a constant and removing the excess frequency component by the Nyquist filter (1084), the signal having the RF transmission frequency (fo) is modulated from the voltage controlled oscillator (1086). Output to the amplifier (1202).
[0010]
On the other hand, the mixer (1102) extracts an envelope signal, that is, an amplitude signal component based on the RF transmission signal obtained from the first terminal and the constant amplitude signal obtained from the second terminal, and the envelope signal is converted into an operational amplifier (1104). ) To the second input. The first input of the operational amplifier (1104) is supplied with an envelope input signal, that is, an analog signal corresponding to the amplitude component of the signal to be transmitted. The operational amplifier (1104) provides a difference signal corresponding to the difference between the signals applied to the first and second inputs to the second input of the modulation amplifier (1202). The modulation amplifier (1202) generates an RF transmission signal based on the signal from the voltage controlled oscillator (1086) and the signal from the operational amplifier (1104), amplifies it by the power amplifier PA (1204), and then transmits it from the antenna (130). To do.
[0011]
In this embodiment, a fractional frequency divider (Fractional-N) is used as the frequency divider (1082), but the present invention is not limited to this. However, the lock-up time can be shortened by using a fractional frequency divider. The lock-up time (τ) is generally calculated based on the following equation based on the frequency (fr) of the local oscillator (1081) and the number of samples.
[0012]
τ = (1 / fr) * (sampling number)
For example, when the frequency (fr) of the local oscillator is 10 kHz and the output of the frequency divider (1082) changes like 1000, 1001, 1002 in accordance with the phase data (104), the voltage controlled oscillator (1086) The resulting frequency varies as 10 kHz * 1000 = 10 MHz, 10.01 MHz, 10.02 MHz. In this case, the lock-up time (τ) is approximately 1/10 k * 100 = 10 msec when the sampling number is 100, for example. In order to shorten the lock-up time, the frequency (fr) of the local oscillator may be increased. However, since the output of the frequency divider can generally take only integer values such as 1000, 1001, and 1002, in this example, The above value (10 msec) is the limit. In this embodiment, since a fractional frequency divider is used instead of a normal frequency divider, the output is not limited to an integer value. In the above case, when the local oscillation frequency (fr) is set to 1 MHz and the output from the fractional frequency divider is changed to 10.00, 10.01, 10.02, the frequency of the signal obtained from the voltage controlled oscillator is As in the case described above, the frequencies are 10.00 MHz, 10.01 MHz, and 10.02 MHz. The lock-up time (τ) in this case is approximately 1/1 MHz * 100 = 100 μsec when the number of samplings is also 100, and the lock-up time is 1/100 compared to the above numerical value (10 msec). be able to.
[0013]
In the present embodiment, the Nyquist filter (1084) is used. However, the present invention is not limited to this, and other types of filters such as a loop filter may be used. However, if a Nyquist filter is used, the transition between symbols can be performed smoothly. In π / 4QPSK, the phase of a signal to be transmitted changes between ± 45 degrees and ± 135 degrees. If the symbol rate of the phase data (104) is 4800 baud, the frequency changes at 45 * 4800/360 = 600 Hz and 135 * 4800/360 = 1800 Hz. For this reason, when a loop filter is used, it is necessary to smoothly perform frequency transition by interpolating between symbols. On the other hand, when using a Nyquist filter, interpolation between symbols is not required. The frequency response characteristic of the loop filter requires a high cutoff characteristic so as not to cause an error in the transition between the interpolated symbols, but the Nyquist filter does not require such a high cutoff frequency and is smooth. This is because of having a good frequency response characteristic.
[0014]
Thus, in this embodiment, since signal processing is performed without using an IQ modulator, digital modulation can be performed satisfactorily without complicating the circuit configuration. Further, since the configuration as in the present embodiment is employed, a saturation amplifier that transmits only the phase component can be used before the amplifier (1202). Thereby, for example, wideband noise generated in a high gain multistage linear amplifier can be suppressed.
[0015]
FIG. 3 is a block diagram showing another embodiment (300) of a digital modulator according to the present invention. Those denoted by the same reference numerals as in FIG. 1 perform the same function. In the embodiment shown in FIG. 3, the first input of the mixer (124) is coupled to the second terminal of the attenuator (122), the second input is coupled to the local oscillator (126), and the output of the mixer (124) is the limiter. (106) and a first input of the mixer (1102). The local oscillator (126) functions as an offset synthesizer. That is, by causing the internal processing frequency of the digital modulator (300) to be different (fi) from the RF transmission frequency (fo), the wraparound of the RF transmission frequency (fo) into the digital modulator (300) is suppressed. To do. Thereby, interference between the transmission frequency and the internal processing frequency can be prevented. The number of elements constituting the circuit increases by the local oscillator (126) and the mixer (124), but the influence on the large wraparound portion of the RF transmission frequency (fo) can be reduced.
[0016]
FIG. 4 is a block diagram showing another embodiment (400) of a digital modulator according to the present invention. The same reference numerals as those in FIGS. 1 and 3 perform the same function. In the embodiment shown in FIG. 4, in addition to the embodiment shown in FIG. 3, a first input coupled to the local oscillator (126), a second input coupled to the output of the voltage controlled oscillator (1086), and a modulation amplifier A mixer (128) is provided having an output coupled to the first input of (1202). In the embodiment shown in FIG. 4, processing is performed in the digital modulator using the internal processing frequency (fi) as in FIG. In the embodiment shown in FIG. 4, a new mixer (128) is required, but the frequency output from the voltage controlled oscillator (1086) is also the internal processing frequency (fi), and the RF transmission frequency (fo) from the antenna (130). Can be further suppressed. Therefore, interference between the transmission frequency and the internal processing frequency can be further prevented.
[0017]
Although the present invention has been described with respect to the π / 4 QPSK modulation system, the present invention is not limited to this. For example, the present invention can be generally used for a single carrier modulation system including 16 QAM (a symbol can be expressed by one vector). Is possible.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a digital modulator according to the present invention.
FIG. 2 shows a block diagram of generating amplitude and phase input data using a DSP.
FIG. 3 is a block diagram showing another embodiment of a digital modulator according to the present invention.
FIG. 4 is a block diagram showing another embodiment of a digital modulator according to the present invention.
[Explanation of symbols]
100, 300, 400 Digital modulator 102 Envelope input signal 104 Phase data 106 Limiter 108 Transmission frequency setter 1081 Local oscillator 1082 Frequency divider 1083 Phase detector 1084 Filter 1086 Voltage controlled oscillator 110 Difference signal generating means 1102 Mixer 1104 Operational amplifier 120 Amplification stage 1202 Modulation amplifier 1204 Power amplifier 122 Attenuator 124, 128 Mixer 126 Local oscillator 130 Antenna

Claims (9)

A digital modulation device (100) for generating an RF transmission signal based on an envelope input signal (102) representing the amplitude of a transmission signal and phase data (104) representing a phase of the transmission signal, the digital modulation device (100) ): A limiter (106) for outputting a constant amplitude signal having a frequency substantially equal to the frequency of the RF transmission signal and having a substantially constant amplitude;
Transmission frequency setting means (108) for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal;
Difference signal generation means (110) for generating a difference signal representing a difference between the envelope signal extracted from the RF transmission signal and the envelope input signal (102);
Amplifying means (120) for generating an RF transmission signal based on the RF transmission frequency (fo) and the difference signal;
The transmission frequency setting means (108) comprises:
A frequency divider (1082) for receiving the phase data (104) and the constant amplitude signal;
A voltage controlled oscillator (1086) that receives the signal from the frequency divider (1082) filtered by the filter (1084) and outputs a signal having an RF transmission frequency;
A digital modulation device (100) comprising: The digital modulator of claim 1, wherein the frequency divider (1082) is a fractional frequency divider. The digital modulator of claim 1, wherein the filter (1084) is a loop filter or a Nyquist filter. A digital modulation device (300) for generating an RF transmission signal based on an envelope input signal (102) representing the amplitude of a transmission signal and phase data (104) representing a phase of the transmission signal, the digital modulation device (100) ):
A limiter (106) for outputting a constant amplitude signal having an internal processing frequency (fi) having a predetermined frequency difference from the frequency of the RF transmission signal and having a substantially constant amplitude;
Transmission frequency setting means (108) for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal;
Difference signal generation means (110) for generating a difference signal representing a difference between the envelope signal extracted from the RF transmission signal and the envelope input signal (102);
Amplifying means (120) for generating an RF transmission signal based on the RF transmission frequency (fo) and the difference signal;
The transmission frequency setter (108) is composed of:
A frequency divider (1082) for receiving the phase data (104) and the constant amplitude signal;
A voltage controlled oscillator (1086) that receives the signal from the frequency divider (1082) filtered by the filter (1084) and outputs a signal having an RF transmission frequency;
A digital modulation device (300) comprising: 5. The digital modulation device according to claim 4, wherein the frequency divider (1082) is a fractional frequency divider. The digital modulation device of claim 4, wherein the filter (1084) is a loop filter or a Nyquist filter. A digital modulation device (400) that generates an RF transmission signal based on an envelope input signal (102) representing the amplitude of a transmission signal and phase data (104) representing a phase of the transmission signal, the digital modulation device (100) ):
A limiter (106) for outputting a constant amplitude signal having an internal processing frequency (fi) having a predetermined frequency difference from the frequency of the RF transmission signal and having a substantially constant amplitude;
Transmission frequency setting means (108) for generating an RF transmission frequency (fo) based on the phase data (104) and the constant amplitude signal;
Difference signal generation means (110) for generating a difference signal representing a difference between the envelope signal extracted from the RF transmission signal and the envelope input signal (102);
Amplifying means (120) for generating an RF transmission signal based on the RF transmission frequency (fo) and the difference signal;
The transmission frequency setting means (108) comprises:
A frequency divider (1082) for receiving the phase data (104) and the constant amplitude signal;
A voltage controlled oscillator (1086) that receives the signal from the frequency divider (1082) filtered by the filter (1084) and outputs a signal having an internal processing frequency (fi);
A mixer (128) for converting a frequency of a signal having the internal processing frequency (fi) into an RF transmission frequency;
A digital modulation device (400) comprising: 8. The digital modulation device according to claim 7, wherein the frequency divider (1082) is a fractional frequency divider. The digital modulation device of claim 7, wherein the filter (1084) is a loop filter or a Nyquist filter.

Images