JP2004015660A - Distortion compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a distortion compensator which performs distortion compensation with high accuracy by matching the delay time even for a signal which has small autocorrelation. <P>SOLUTION: A distortion compensator is provided with a zero-cross point calculater 11 for calculating the time that a digital signal converted through an A/D convertor 4 becomes zero in amplitude, a zero-cross point calculater 12 for calculating the time that an input signal becomes zero in amplitude, and a controller 13 for supplying time difference calculated by the zero-cross point calculaters 11 and 12 to an interpolation filter 5 and a delay device 6 as a delay control variable. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a distortion compensator of a digital predistortion method, which has a function of comparing an input signal with a feedback signal from a power amplifier and obtaining a distortion compensation coefficient from the difference to perform an adaptive operation. Things.
[0002]
[Prior art]
In a transmitter for wireless communication, distortion due to non-linearity of a power amplifier not only deteriorates signal quality, but also results in leakage power to an adjacent channel. Therefore, a predistortion method that compensates for nonlinearity without lowering the power efficiency of the power amplifier is essential.
[0003]
FIG. 4 is a block diagram showing a conventional distortion compensator using a predistortion method. In the figure, reference numeral 1 denotes a multiplier for multiplying an input signal by a distortion compensation coefficient, and 2 denotes a D for converting a digital signal to an analog signal. The / A converter 3 is a power amplifier that amplifies and outputs an analog signal. Reference numeral 4 denotes an A / D converter that converts an analog signal that has been amplified by the power amplifier 3 and is partially fed back into a digital signal. Reference numeral 5 denotes an interpolation filter that calculates an amplitude value obtained by shifting the digital signal in accordance with a delay control amount. Is a delay unit for delaying an input signal according to a delay control amount. Reference numeral 7 denotes a compensation coefficient calculation unit for calculating a distortion compensation coefficient for each amplitude of the input signal according to the input signal delayed by the delay unit 6 and the amplitude value calculated by the interpolation filter 5, and 8 denotes an instantaneous amplitude of the input signal. The amplitude calculator 9 for calculating stores the distortion compensation coefficient for each amplitude of the input signal calculated by the compensation coefficient calculator 7 and calculates the distortion compensation coefficient corresponding to the instantaneous amplitude of the input signal calculated by the amplitude calculator 8. This is a memory supplied to the multiplier 1. Reference numeral 10 denotes a correlator that calculates a correlation value between the input signal and the digital signal converted by the A / D converter 4 and controls the delay time of the delay unit 6 to a delay time at which a maximum correlation value is obtained.
[0004]
Next, the operation will be described.
The input signal is a digital signal. The input signal is multiplied in the multiplier 1 by a distortion compensation coefficient corresponding to the instantaneous amplitude. The multiplied output is converted into an analog signal by the D / A converter 2, amplified by the power amplifier 3, and output. Part of the output of the power amplifier 3 is fed back as a feedback signal. The feedback signal is converted into a digital signal by the A / D converter 4, and the amplitude value shifted according to the delay control amount is calculated by the interpolation filter 5 and output to the compensation coefficient calculation unit 7.
On the other hand, the input signal is delayed by the delay unit 6 in accordance with the delay control amount, and the timing of inputting the delayed input signal and the feedback signal to the compensation coefficient calculation unit 7 is adjusted.
The difference between the input signal and the feedback signal represents a distortion component generated in the power amplifier 3. In the compensation coefficient calculation unit 7, a distortion compensation coefficient that cancels the nonlinearity of the power amplifier 3 is obtained for each amplitude from the instantaneous amplitude of the input signal and the value of the distortion at the amplitude. This distortion compensation coefficient is stored in the memory 9, and a distortion compensation coefficient corresponding to the instantaneous amplitude of the input signal calculated by the amplitude calculator 8 is selected from the memory 9 and supplied to the multiplier 1.
As described above, it is necessary to match the timing at which the input signal and the feedback signal are input to the compensation coefficient calculator 7. The approximate value of the delay time of the feedback signal is known, and the correlator 10 calculates the product of the input signal and the feedback signal shifted several clock times before and after the approximate delay time as a center, and calculates the feedback signal from the result. The signal delay time is obtained by calculation.
From the result, the delay amount of the delay unit 6 and the interpolation filter 5 is controlled. For example, when the time difference is equivalent to 12.2 clocks in one clock cycle, the delay time of the delay unit 6 is controlled to the number of delays of 13 clocks, and the interpolation filter 5 calculates a waveform delayed by 0.8 clocks. Is controlled to be output.
[0005]
[Problems to be solved by the invention]
Since the conventional distortion compensator is configured as described above, the delay time is obtained from the correlation between the input signal and the feedback signal by the correlator 10, and in this case, the signal itself has strong autocorrelation. However, the autocorrelation is not accurately obtained for a small signal. In general, even in a signal having strong autocorrelation, since the correlation value has a gentle convex shape, a time error obtained by calculation may be a magnitude that cannot be ignored.
As described above, there has been a problem that a delay time cannot be accurately adjusted for a signal having a small autocorrelation, and a highly accurate distortion compensation process cannot be performed.
[0006]
The present invention has been made to solve the above problems, and has as its object to obtain a distortion compensator that performs a highly accurate distortion compensation process by adjusting the delay time even for a signal having a small autocorrelation. I do.
[0007]
[Means for Solving the Problems]
The distortion compensator according to the present invention includes a first zero-crossing detector for detecting a time when the digital signal converted by the A / D converter has zero amplitude, and a second zero-crossing detector for detecting a time when the digital input signal has zero amplitude. 2 zero-cross detecting means, and control means for supplying a time difference detected by the first and second zero-cross detecting means to the interpolation filter means and the delay means as a delay control amount.
[0008]
A distortion compensator according to the present invention includes a signal generation unit that generates a signal in which a digital input signal intermittently has a zero amplitude, and a zero cross that detects a time when a digital signal converted by an A / D conversion unit has a zero amplitude. The detecting means, and a time difference between the time when the digital input signal generated by the signal generating means has zero amplitude and the time when the amplitude becomes zero detected by the zero-cross detecting means is used as a delay control amount as interpolation control means and delay means. Supply means.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a distortion compensator using a predistortion method according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes a multiplier (multiplication means) for multiplying an input signal by a distortion compensation coefficient; Reference numeral denotes a D / A converter (D / A conversion means) for converting a digital signal into an analog signal, and reference numeral 3 denotes a power amplifier (power amplification means) for amplifying and outputting an analog signal. Reference numeral 4 denotes an A / D converter (A / D conversion means) for converting an analog signal partially amplified by the power amplifier 3 and fed back to a digital signal, and 5 denotes an amplitude value obtained by shifting the digital signal according to a delay control amount. Is a delay device (delay means) for delaying the input signal according to the delay control amount. Reference numeral 7 denotes a compensation coefficient calculator (distortion compensation coefficient calculator) that calculates a distortion compensation coefficient for each amplitude of the input signal according to the input signal delayed by the delay unit 6 and the amplitude value calculated by the interpolation filter 5. Is an amplitude calculator (distortion compensation coefficient calculator) for calculating the instantaneous amplitude of the input signal, 9 is a distortion compensation coefficient for each amplitude of the input signal calculated by the compensation coefficient calculator 7, and is calculated by the amplitude calculator 8. And a memory (distortion compensation coefficient calculating means) for supplying a distortion compensation coefficient corresponding to the instantaneous amplitude of the input signal to the multiplier 1.
Numeral 11 denotes a zero-crossing point calculating unit (first zero-crossing detecting means) for calculating the time when the digital signal converted by the A / D converter 4 has zero amplitude, and 12 denotes zero-crossing for calculating the time when the input signal has zero amplitude. A point calculator (second zero-crossing detector) 13 is a controller (controller) that supplies the mutual time difference calculated by the zero-crossing point calculators 11 and 12 to the interpolation filter 5 and the delay unit 6 as a delay control amount. is there.
FIG. 2 is a waveform diagram showing an input signal and a feedback signal according to the first embodiment of the present invention.
[0010]
Next, the operation will be described.
The input signal is a digital signal. The input signal is multiplied in the multiplier 1 by a distortion compensation coefficient corresponding to the instantaneous amplitude. The multiplied output is converted into an analog signal by the D / A converter 2, amplified by the power amplifier 3, and output. Part of the output of the power amplifier 3 is fed back as a feedback signal. The feedback signal is converted into a digital signal by the A / D converter 4, and the amplitude value shifted according to the delay control amount is calculated by the interpolation filter 5 and output to the compensation coefficient calculation unit 7.
On the other hand, the input signal is delayed by the delay unit 6 in accordance with the delay control amount, and the timing of inputting the delayed input signal and the feedback signal to the compensation coefficient calculation unit 7 is adjusted.
The difference between the input signal and the feedback signal represents a distortion component generated in the power amplifier 3. In the compensation coefficient calculation unit 7, a distortion compensation coefficient that cancels the nonlinearity of the power amplifier 3 is obtained for each amplitude from the instantaneous amplitude of the input signal and the value of the distortion at the amplitude. This distortion compensation coefficient is stored in the memory 9, and a distortion compensation coefficient corresponding to the instantaneous amplitude of the input signal calculated by the amplitude calculator 8 is selected from the memory 9 and supplied to the multiplier 1.
As described above, it is necessary to match the timing at which the input signal and the feedback signal are input to the compensation coefficient calculator 7.
[0011]
FIG. 2 shows the waveforms of the input signal and the feedback signal. The input signal is a digital value and is digital data having an amplitude at the timing indicated by the arrow. On the other hand, the feedback signal is converted into a digital signal in the A / D converter 4. The feedback signal has a small amplitude at a point with a large amplitude due to the non-linear characteristic of the power amplifier 3.
In the first embodiment, the zero-crossing point calculation unit 11 calculates and obtains a point where the amplitude of the feedback signal becomes zero from data before and after. Similarly, the zero-cross point calculation unit 12 obtains a point where the amplitude of the input signal becomes zero. The controller 13 determines the time difference between the two zero cross patterns and supplies the time difference to the delay unit 6 and the interpolation filter 5 as a delay control amount.
For example, when the time difference is equivalent to 12.2 clocks in one clock cycle, the delay time of the delay unit 6 is controlled to the number of delays of 13 clocks, and the interpolation filter 5 calculates a waveform delayed by 0.8 clocks. Is controlled to be output.
[0012]
As described above, according to the first embodiment, even if the input signal itself is a signal having a small autocorrelation, the delay time can be accurately obtained, and a highly accurate distortion compensation process can be performed. .
The non-linearity of the output signal from the power amplifier 3 is such that the gain is reduced at a large amplitude, the linearity is maintained at a small amplitude portion, and the amplitude is zero, so that there is no influence of distortion even without distortion compensation. Things. Therefore, even before the distortion compensation processing by the multiplier 1, the delay time can be accurately detected from the time when the amplitude becomes zero by the zero-crossing point calculation unit 11.
[0013]
Embodiment 2 FIG.
FIG. 3 is a block diagram showing a distortion compensator using a predistortion method according to a second embodiment of the present invention. In FIG. 3, reference numeral 14 denotes a signal generator for generating a signal in which an input signal intermittently becomes zero in amplitude. (Signal generating means) and 15 represent the time difference between the time when the input signal generated by the signal generator 14 has zero amplitude and the time when the zero-crossing point calculator (zero-cross detecting means) 11 has zero amplitude. The controller (control means) supplies the delay control amount to the interpolation filter 5 and the delay unit 6.
Other configurations are the same as those in FIG.
[0014]
Next, the operation will be described.
The signal generator 14 generates a signal having a known zero cross point as an input signal, passes the signal through a device for a certain period of time such as when the power is turned on, and reduces the amplitude of the feedback signal to zero by the zero cross point calculation unit 11 as in the first embodiment. Find the time The controller 15 uses the time difference between the time when the input signal generated by the signal generator 14 becomes zero amplitude and the time when the amplitude becomes zero detected by the zero-crossing point calculation unit 11 as a delay control amount and the interpolation filter 5 and It is supplied to the delay unit 6.
[0015]
As described above, according to the second embodiment, even if the input signal itself is a signal having low autocorrelation, the delay time can be accurately obtained, and a highly accurate distortion compensation process can be performed. .
The time when the amplitude of the input signal, which is the reference for detecting the delay time, becomes zero is not a signal detected by the zero-crossing point calculation unit 12 but a signal generated by the signal generator 14. , And more accurately.
[0016]
【The invention's effect】
As described above, according to the present invention, the first zero-cross detecting means for detecting the time at which the digital signal converted by the A / D converting means has zero amplitude, and the time at which the digital input signal has zero amplitude is detected. A second zero-crossing detecting means, and a control means for supplying a time difference between the first and second zero-crossing detecting means to the interpolation filter means and the delaying means as a delay control amount. Even if the digital input signal itself has a small autocorrelation, the delay time of the digital signal converted from the digital input signal by the A / D converter can be accurately obtained, and a highly accurate distortion compensation process can be performed. Can be applied.
The non-linearity of the output signal by the power amplifying means that the gain decreases at a large amplitude, the linearity is maintained at a small amplitude portion, and the amplitude is zero, and the distortion is affected even without distortion compensation. There is no. Therefore, even before the distortion compensation processing by the multiplication means, there is an effect that the delay time can be accurately detected from the time when the amplitude becomes zero by the first zero-cross detection means.
[0017]
According to the present invention, there are provided signal generating means for generating a signal in which a digital input signal has an amplitude of zero intermittently, and zero-cross detecting means for detecting a time when a digital signal converted by an A / D converter has an amplitude of zero. Control for supplying the time difference between the time when the digital input signal generated by the signal generating means has zero amplitude and the time when the amplitude becomes zero detected by the zero-cross detecting means to the interpolation filter means and the delay means as a delay control amount. Means for accurately obtaining the delay time of a digital signal converted from a digital input signal by an A / D converter even if the digital input signal itself is a signal having low autocorrelation. Thus, highly accurate distortion compensation processing can be performed.
The time when the amplitude of the digital input signal, which is the reference for detecting the delay time, becomes zero is not a signal detected by the zero-crossing detecting means but a signal generated by the signal generating means, so that the delay time can be detected more accurately. can do.
The non-linearity of the output signal by the power amplifying means that the gain decreases at a large amplitude, the linearity is maintained at a small amplitude portion, and the amplitude is zero, and the distortion is affected even without distortion compensation. There is no. Therefore, even before the distortion compensation processing by the multiplication means, there is an effect that the delay time can be accurately detected from the time when the amplitude becomes zero by the first zero-cross detection means.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a distortion compensator using a predistortion method according to a first embodiment of the present invention.
FIG. 2 is a waveform chart showing an input signal and a feedback signal according to the first embodiment of the present invention.
FIG. 3 is a block diagram showing a distortion compensator using a predistortion method according to a second embodiment of the present invention.
FIG. 4 is a block diagram showing a distortion compensator using a conventional predistortion method.
[Explanation of symbols]
Reference Signs List 1 multiplier (multiplication means), 2 D / A converter (D / A conversion means), 3 power amplifier (power amplification means), 4 A / D converter (A / D conversion means), 5 interpolation filter (interpolation) Filter unit), 6 delay unit (delay unit), 7 compensation coefficient operation unit (distortion compensation coefficient operation unit), 8 amplitude calculation unit (distortion compensation coefficient operation unit), 9 memory (distortion compensation coefficient operation unit), 11 zero crossing point Calculator (first zero-crossing detector, zero-crossing detector), 12 zero-crossing point calculator (second zero-crossing detector), 13, 15 controller (controller), 14 signal generator (signal generator).

Claims (2)

Multiplying means for multiplying the digital input signal by a distortion compensation coefficient to perform a distortion compensation process;
D / A conversion means for converting the digital signal subjected to the distortion compensation processing by the multiplication means into an analog signal,
Power amplification means for amplifying and outputting the analog signal converted by the D / A conversion means;
A / D conversion means for converting an analog signal amplified and fed back by the power amplification means into a digital signal;
Interpolation filter means for calculating an amplitude value obtained by shifting the digital signal converted by the A / D conversion means according to the delay control amount;
Delay means for delaying the digital input signal according to the delay control amount;
Distortion compensation coefficient calculation means for calculating a distortion compensation coefficient in accordance with the digital input signal delayed by the delay means and the amplitude value calculated by the interpolation filter means and supplying the calculated distortion compensation coefficient to the multiplication means,
First zero-cross detecting means for detecting a time when the digital signal converted by the A / D converting means has an amplitude of zero;
Second zero-crossing detecting means for detecting a time when the digital input signal becomes zero in amplitude;
A distortion compensator comprising: control means for supplying a time difference detected by the first and second zero-cross detection means to the interpolation filter means and the delay means as a delay control amount. Signal generating means for generating a signal in which the digital input signal has an amplitude of zero intermittently;
Multiplying means for multiplying the digital input signal by a distortion compensation coefficient to perform a distortion compensation process;
D / A conversion means for converting the digital signal subjected to the distortion compensation processing by the multiplication means into an analog signal,
Power amplification means for amplifying and outputting the analog signal converted by the D / A conversion means;
A / D conversion means for converting an analog signal amplified and fed back by the power amplification means into a digital signal;
Interpolation filter means for calculating an amplitude value obtained by shifting the digital signal converted by the A / D conversion means according to the delay control amount;
Delay means for delaying the digital input signal according to the delay control amount;
Distortion compensation coefficient calculation means for calculating a distortion compensation coefficient in accordance with the digital input signal delayed by the delay means and the amplitude value calculated by the interpolation filter means and supplying the calculated distortion compensation coefficient to the multiplication means,
Zero-cross detection means for detecting a time when the digital signal converted by the A / D conversion means has an amplitude of zero;
The time difference between the time when the digital input signal generated by the signal generating means has zero amplitude and the time when the amplitude becomes zero detected by the zero-cross detecting means is used as a delay control amount for the interpolation filter means and the delay means. A distortion compensator provided with a control unit for supplying the distortion.

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