JP2000261252A - Distortion compensation power amplification circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the circuit scale of a distortion compensation power amplification circuit where envelope feedback control is applied to the complex synthesis PD method and to reduce the cost. SOLUTION: Part of an input signal before being divided into two by a distributor 11 is extracted by a directional coupler 10 and is subjected to envelope detection by a detector 23 to obtain a reference input of an error detector 24. Meanwhile, part of the output of a power amplifier 18 is extracted and the signal obtained by envelope detection is inputted to the error detector 24 to detect the difference (distortion component) from the reference input. A control part 25 controls the amplitude and phase of the tertiary distortion of the opposite polarity generated by a tertiary distortion generator 13 so that this difference is made 0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier circuit of a transmitter mounted on a base station radio equipment for digital mobile communication in the VHF and UHF bands, and more particularly, to increase power efficiency by suppressing distortion generated in a power amplifier. And a power amplification circuit to which a distortion compensation circuit is added.

[0002]

2. Description of the Related Art A power amplifier circuit using a power transistor is provided in a base station transmitter for digital mobile communication. The power amplifier circuit of the base station is a class A or class AB operation having good linearity, high output, and low distortion, and a circuit using a parallel synthesis or push-pull configuration is generally used at the final stage.

FIG. 3 is an example of input / output characteristics of a power amplifier. It is an example of the characteristics of the output power P _OUT and the third-order distortion with respect to the input power P _IN of the digitally modulated single carrier signal (CW). When the input power P _IN increases, the output power P _OUT with third-order distortion is 1: increases along the third slope, the output power P _OUT becomes remarkable to increase, according to the non-linear region (third-order distortion deterioration point) . The difference between that point and the output power is the third-order intermodulation distortion (IM ₃ ). Also, this figure shows, for example, the leakage power (ACP) for the adjacent channel in the transmission output when the input signal is a digital signal subjected to π / 4 shift QPSK modulation.

As described above, when the input power increases, the input / output characteristics show nonlinearity. In the case of a digitally modulated single carrier, when the input power increases, a distortion component is included in the output power. become. In the case of a multi-frequency signal, as the input increases, intermodulation distortion (IM ₃ ) occurs. When such distortion occurs, it is regulated as spurious radiation, so that the maximum output is limited to a value considerably lower than the saturation level of the amplifier, and the power efficiency of the amplifier is reduced.

As can be seen from the figure, the above-mentioned output deterioration due to an increase in single carrier input and intermodulation distortion due to multi-frequency input are mainly due to the generation of third-order distortion.
A number of distortion compensation techniques for compensating for such third-order distortion have been developed and put into practical use.

[0006] Predistortion (PD) is one of distortion compensation techniques, and a predistortion circuit (PD circuit: predistortion compensation) for generating a signal for canceling a distortion component generated in a power amplifier at a stage preceding the power amplifier. Circuit) to offset the distortion generated by the power amplifier to improve the amount of distortion and improve power efficiency.

FIG. 4 is a block diagram of a conventional distortion compensation power amplifier circuit. This example is a distortion-compensated power amplifier circuit in which envelope feedback control is applied to the complex synthesis PD method. In the figure,
11 is a distributor, 12 is a PD circuit, 13 is a distortion generator, 14
Is a variable attenuator, 15 is a variable phase shifter, 16 is a delay line, 17
Is a combiner, 18 is a power amplifier, 19 is a directional coupler, 2
0 is a detector, 21 is a control unit, and 22 is a memory.

For example, as an input signal, a π / 4 shift QP
The SK-modulated single carrier signal is input,
1 to the delay line 16 and the PD circuit 12. P
The distortion generator 13 of the D circuit 12 is a tertiary distortion generator, inverts the polarity of the digitally modulated input signal of a single carrier to generate tertiary distortion, and outputs a non-distorted positive (non-inverted) carrier input. The signal is combined with the signal to cancel the carrier component, and only the third-order distortion of the opposite polarity is output. The output is adjusted in amplitude and phase by a variable attenuator 14 and a variable phase shifter 15, and is combined with a signal via a delay line 16 by a combiner 17. The synthesized signal is amplified by the power amplifier 18, at which time the power amplifier 18
Is canceled by the third-order distortion component of the opposite polarity generated by the PD circuit 12, and a transmission output with distortion compensated is obtained. In order to detect the residual distortion included in the transmission output, a part thereof is extracted by the directional coupler 19,
The envelope is detected by the detector 20 and sent to the control unit 21.

On the other hand, the waveform data after the envelope detection when the transmission output is no distortion is stored in the memory 22 in advance, and the control unit 21 stores the data input from the detector 20 in the memory 22. The values of the variable attenuator 14 and the variable phase shifter 15 are controlled such that the difference (distortion component) becomes zero with the data.

[0010]

However, in the above-mentioned conventional distortion-compensated power amplifier circuit, since the amount of waveform data after envelope detection stored in the memory 22 is large,
There is a problem that the circuit scale is large and expensive. Further, when a large number of transmitters equipped with such a distortion compensation power amplifier circuit are manufactured in a factory, waveform data obtained by analyzing an output signal in a non-distortion state varies due to variations in performance of components of the power amplifier. A large number of products must be measured one by one and the data must be stored in the memory 22, which causes a problem that the number of steps is increased and the cost cannot be reduced.

An object of the present invention is to solve the above-mentioned conventional problems. A simple circuit is added to omit a memory to reduce a circuit scale of a distortion compensation power amplifier circuit. It is an object of the present invention to provide a distortion-compensated power amplifier circuit in which a large number of devices are manufactured, the adjustment work for each device is eliminated, the number of steps is reduced, and the cost is reduced.

[0012]

SUMMARY OF THE INVENTION A distortion-compensated power amplifier circuit according to the present invention generates a digitally modulated input signal of a single carrier and amplifies the input signal as a transmission output. And a divider that divides the input signal into two in order to suppress a distortion component that becomes leakage power with respect to the input signal. A distortion generator that generates a third-order distortion of opposite polarity, a variable attenuator that changes the amplitude of the output of the distortion generator by a control signal,
A variable phase shifter that changes the phase shift amount of the output of the variable attenuator by a control signal, and a signal obtained by delaying the output of the variable phase shifter and the other signal divided into two by the distributor. A combiner, a power amplifier that power-amplifies the signal combined by the combiner and generates a transmission output, a first detector that extracts a part of the input signal and performs envelope detection, A second detector for extracting a part and detecting the envelope;
An error detector that outputs a distortion component, which is a difference between the output of the second detector and the distortion-free envelope detection output that is output from the detector as a reference signal, and an output from the error detector. A control unit that supplies the control signal such that the output distortion component becomes zero to the variable attenuator and the variable phase shifter, wherein the distortion generated in the power amplifier and becoming leakage power to an adjacent channel is provided. The components are configured to be offset by third-order distortion of the opposite polarity generated by the distortion generator.

[0013]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, a PD circuit 12 and a delay line 16 between a distributor 11 and a combiner 17 and a power amplifier 1
8. The directional coupler 19 and the detector 20 are the same as the conventional one. 10 is a directional coupler for extracting a part of the input signal, 2
Reference numeral 3 denotes a detector for detecting the envelope of the extracted input signal, and reference numeral 24 denotes an error detector. The detector 23 on the input side and the detector 20 on the output side both detect a signal that is faithfully input, and use a directional coupler or a resistive attenuator to detect the comparison error (distortion component) without fail. The levels have been adjusted to be almost the same.

The error detector 24 is constituted by a differential amplifier circuit. For example, an error-free envelope signal obtained by envelope-detecting the digitally-modulated input signal of π / 4 shift QPSK by the detector 23 is used as a comparison criterion. A difference (distortion component) between the transmission output and the signal detected by the envelope detection by the detector 20 is obtained and given to the control unit 25. The control unit 25 controls the variable attenuator 14 and the variable phase shifter 15 so that the distortion component becomes zero.

As described above, in the present invention, a conventional memory is omitted by using a distortion-free envelope signal obtained by envelope-detecting a part of an input signal as a reference signal, and a part of a power-amplified transmission output is obtained. Is compared with a signal obtained by envelope detection to extract a distortion component included in the transmission output, and cancel the distortion of the transmission output by controlling the amplitude and phase of the distortion component for cancellation generated by the distortion generator 13; The gist is to increase the power efficiency of the power amplifier 18.

FIG. 2 is a frequency spectrum of a transmission output showing the effect of the present invention. The power of a predetermined band in the plus side adjacent channel ((+) Adj.ch.) And the minus side adjacent channel ((−) Adj.ch.) Of the transmission frequency f ₀ , that is,
The adjacent channel leakage power (ACP) is “-38.75 dB on the (+) side and −38.00 d on the (−) side when the compensation is“ none ”.
B), when compensation is present ((+) side -48.0)
0 dB, -49.25 dB on the (-) side), an improvement of about 10 dB was obtained, and an extremely large improvement in practical use was obtained.

FIG. 3 shows the characteristics of the ACP in the input / output characteristics of the power amplifier, as described above.
dB improvement has been obtained. The distortion improvement amount is about 1 in consideration of the effect of reducing power consumption even in the case of 2-3 dB.
The 0 dB improvement is a very significant improvement.

[0018]

As described in detail above, by implementing the present invention, the memory can be omitted by simply adding a simple circuit, so that the circuit scale can be reduced and the cost can be reduced. Further, the number of adjustment steps when producing a large number of transmitters is reduced, which is extremely effective in reducing the cost of the apparatus. Further, the present invention provides a W-CDMA (Wideband CDMA) for a next generation mobile communication system.
band Code Division Multiple Access) system.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a frequency spectrum of a transmission output showing the effect of the present invention.

FIG. 3 is an example of input / output characteristics of a power amplifier showing the effects of the present invention.

FIG. 4 is a block diagram of a conventional distortion compensation power amplifier circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10, 19 Directional coupler 11 Divider 12 PD circuit 13 Distortion generator 14 Variable attenuator 15 Variable phase shifter 16 Delay line 17 Synthesizer 18 Power amplifier 20 Detector 21 Control part 22 Memory 23 Detector 24 Error detector 25 Control part

Claims (1)

[Claims] In order to suppress a distortion component which is generated due to nonlinearity of a power amplifier and becomes leakage power to an adjacent channel when a digitally modulated input signal of a single carrier is power-amplified as a transmission output, A splitter for splitting an input signal into two, a distortion generator for inputting one of the signals split by the splitter and generating a third-order distortion having a polarity opposite to that of a distortion caused by nonlinearity of the power amplifier; A variable attenuator that changes the amplitude of the output of the distortion generator by a control signal; a variable phase shifter that changes the amount of phase shift of the output of the variable attenuator by a control signal; and the output of the variable phase shifter A combiner that combines a signal obtained by delaying the other signal divided into two by the divider, a power amplifier that power-amplifies the signal combined by the combiner to generate a transmission output, and a part of the input signal Extract and envelope A first detector for detecting, a second detector for extracting a part of the transmission output and performing envelope detection, and a distortion-free envelope detection output output from the first detector as a reference signal. And an error detector that outputs a distortion component that is the difference between the output of the second detector and the control signal such that the distortion component output from the error detector becomes zero. A variable attenuator and a control unit for giving to the variable phase shifter, wherein the distortion component generated by the power amplifier and serving as leakage power to an adjacent channel is generated by the third-order distortion of the opposite polarity generated by the distortion generator. A distortion-compensated power amplifier circuit configured to cancel.