KR100313919B1 - Predistortion Power Amplifier having gain and phase compens ation function - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power amplifier, and more particularly, to a line distortion power amplifier having a gain and phase compensation function capable of compensating for distortion of a signal due to a change in operating conditions, which has been a conventional problem. The power amplifier according to the present invention includes a first directional coupler for splitting an input signal into two first signals and a second signal, and a variable attenuator for gain compensation generated at the power amplifier output by the first signal separated from the first directional coupler. A variable phase shifter to compensate for phase, a linearizer to reduce the distortion component in the power amplifier output, a power amplifier to amplify the signal output from the linearizer, and a signal output from the power amplifier into two output signals And an error signal detection unit for comparing the second signal separated from the first directional coupler and the output signal output from the second directional coupler to detect amplification gain and phase change.

Description

Predistortion Power Amplifier having gain and phase compensation function

FIELD OF THE INVENTION The present invention relates to power amplifiers and, more particularly, to predistortion power amplifiers.

In general, an amplifier increases the power of an electrical signal input to the amplifier. An ideal amplifier would only linearly increase the level or amplitude of the input signal without any distortion.

However, all amplifiers inevitably cause distortion in the output signal due to the nonlinear nature of the active elements. Distortion in the amplifier is caused by two factors: the gain decrease as the input signal increases and the phase change as the input signal increases.

Thus, predistortion and feed-forward methods are generally used to improve the linear characteristics of power amplifiers. In particular, the linear distortion amplifier of the predistortion method is widely used in mobile communication base stations due to the advantage of improving the linear characteristics of the amplifier without much deterioration of the power amplifier efficiency.

The operation principle of a linearization amplifier using predistortion is as follows.

Most power amplifiers have a nonlinear characteristic in which the gain decreases and the phase is delayed as the input signal increases. A linearizer using predistortion is placed in front of this nonlinear power amplifier. The linearizer using predistortion has the advantage of linearizing the overall gain and phase change characteristics of the amplifier. In addition, the linearizer using predistortion has an advantage that the configuration is simple and that the efficiency decrease due to the linearizer connection is hardly generated.

However, the linearizer using predistortion has a problem that there is no compensation function according to changes in operating temperature, input power, and time of the power amplifier. Therefore, it is necessary to detect and compensate for the gain and phase change generated in the power amplifier according to the change of operating conditions.

Various linearization devices have been developed to improve the distortion characteristics of power amplifiers used in wireless base station equipment for mobile communication or personal mobile communication. FIG. 1 illustrates a linearization apparatus configured by applying a feed-forward method among such linearization apparatuses.

The general feedforward linearization apparatus 100 generates an error signal by comparing the distortion signal generated from the main amplifier with the input signal of the power amplifier, and adds the error signal to the output of the main amplifier in reverse phase to distort the power amplifier. Improves. In the line distortion method shown in FIG. 1, a small transistor is used to generate an error signal, and the error signal is input to the power amplifier in addition to the input signal as a reference signal.

The linearization apparatus of the predistortion method shown in FIG. 1 adjusts an input port into which a signal to be predistorted is input, an ultra short amplifier 101 for amplifying the input signal, and an intensity of the amplified signal. Variable signal attenuator 102, a divider 103 for dividing the attenuated signal into two paths, an error signal generator 108 for detecting an error signal of the amplifier, and a signal delay circuit unit for linearly changing the input signal. 107, the magnitude of the signal output from the combiner 104 and the combiner 104 which combines the signal output from the error signal generation unit 108 and the signal output from the signal delay circuit unit 107. The signal attenuator 105, and the termination amplifier 106 for amplifying the signal output from the signal attenuator 105.

The error signal generator 108 includes a hybrid combiner 109 having two output signals having a phase difference of 90 degrees, a linear circuit unit 111 and a hybrid combiner 109 in which a signal output from the hybrid combiner 109 changes linearly. The non-linear circuit section 112 in which the signal output from the non-linearly varies, and the variable signal attenuator for changing the magnitude and phase of the signal output from the hybrid coupler 109, and the variable phase shifter 118. In addition, the signal delay circuit unit 107 is composed of a delay line so that the input signal has a time delay characteristic.

The power amplifier using the linearizer is as shown in FIG. The operating principle of the power amplifier shown in FIG. 1 is as follows.

The RF band signal input through the input port is amplified by the ultra short amplifier 101 having excellent linear characteristics. The signal amplified by the ultra-short amplifier 101 is divided into an error signal generator 108 and a signal delay circuit 107 through a signal attenuator 102 and a divider 103. The error signal detector 108 generates a correction signal having the same magnitude as the error signal generated by the power amplifier, and adjusts the magnitude and phase of the correction signal.

The reference signal input to the power amplifier in the signal delay circuit 107 is an original input signal that is not predistorted. The respective signals output from the error signal generator 108 and the signal delay circuit 107 are combined by the combiner 104 and then passed through the signal attenuator 105 and the termination amplifier 106 to the power amplifier 200. Is entered.

The variable signal attenuator 102 for controlling the strength of the signal amplified by the ultra-short amplifier 101 is composed of a hybrid coupler and a pin diode, and determines the degree of attenuation by appropriately adjusting the bias voltage of the pin diode. . The role of this signal attenuator 102 is used to keep the overall gain of the linearization circuit constant.

The signal input to the error signal generator 108 among the input signals divided into two paths by the divider 103 is divided into two paths by the hybrid combiner 109 again. The signals divided by the hybrid coupler are input to the linear circuit unit 111 and the nonlinear circuit unit 112, respectively. At this time, the signal having the same phase as the input signal of the hybrid coupler is input to the linear circuit section 111, and the signal having a phase difference of 90 degrees with the input signal of the hybrid coupler is input to the nonlinear circuit section 112.

The signal input to the linear circuit section 111 is attenuated by the fixed signal attenuator 113 having a PI type attenuator structure, the intensity of the signal is amplified linearly by the amplifier 114, the non-linear circuit section The signal input to 112 is directly input to the amplifier 115 and the magnitude of the signal is amplified. The signal output from the linear circuit unit and the signal output from the nonlinear circuit unit are both input to the input port of the hybrid coupler 110, respectively. At this time, the amplifier for amplifying the signal input to the nonlinear circuit section 112 is the same as the amplifier of the linear circuit section 111, it is adjusted to have a distortion characteristic similar to the distortion characteristic of the power amplifier.

Since the signal of the linear circuit unit 111 and the signal of the nonlinear circuit unit 112 exhibit a 180 degree phase difference, the signal output from the hybrid coupler 110 is eventually output from the signal output from the linear circuit unit 111 and the nonlinear circuit unit 112. It is the difference of the output signal. The signal output from the hybrid coupler 110 is a correction signal for correcting the error of the power amplifier. The correction signal is input to the combiner 104 after the size and phase are changed by the variable signal attenuator and the variable phase transformer 118.

The signal delay circuit unit 107 is composed of a delay line for compensating for the time delay generated in the error signal generation unit 108 and applies a signal to the input port of the combiner 104. Then, the signal summed by the combiner 104 is adjusted by the signal attenuator 105 and then amplified by the terminal amplifier 106 having excellent linear characteristics and input to the power amplifier 200.

However, the conventional power amplifier has a linear characteristic depending on the characteristics of the components, so the longer the use time, the greater the error of the signal, the characteristics of the device and the power amplifier changes according to the operating temperature of the power amplifier, the linear characteristics are deteriorated There is this.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to provide a power amplifier control circuit capable of compensating an operating temperature and a gain change of a power amplifier and a phase change of a signal.

1 is a block diagram schematically showing a conventional power amplifier equipped with a linearization device.

2 is a block diagram schematically illustrating a power amplifier of the present invention in which a gain and phase compensation circuit is implemented.

3 is a block diagram illustrating an error signal detector in the power amplifier of FIG.

Explanation of symbols for main parts of the drawings

1000: Linearizer 1101, 1114, 1106, 1115: Amplifier

1102 variable attenuator 1103 divider

1105, 1113, 1116: signal attenuator 1106: termination amplifier

1109, 1110: hybrid combiner 1117: variable signal attenuator

1118: variable phase displacement 1119: delay line

2000: Error signal detector 2100, 2300, 2400: Low pass filter

2200: Op amp 2500, 2600: Limiter

3000: power amplifier

According to the present invention, as shown in FIG. 2, one of an input port into which an RF signal is input and a signal separated from the directional coupler and the directional coupler separating the input signal into two paths is changed in the operating condition of the power amplifier 3000. Variable attenuator 1102 for gain compensation, variable phase shifter 1118 for phase shift compensation, linearizer 1000 for reducing distortion generated in power amplifier 3000, and linearizer Directional coupler for sampling the signal output from the power amplifier 3000 and the power amplifier 3000, and a delay line, input signal and output to compensate the time delay between the input signal and the output signal Characterized in that it consists of an error signal detection unit for comparing the signal to detect the gain and phase change.

The first directional coupler divides the input signal input through the input port into two paths and separates the first signal and the second signal. The variable attenuator 1102 changes the gain compensation of the first signal among the signals separated by the first directional coupler, and the variable phase shifter 1118 compensates the phase of the signal output from the variable attenuator 1102. .

The linearizer 1000 reduces the distortion component of the signal output from the variable phase transformer 1118. The linearizer 1000 includes an ultra short amplifier 1101 for amplifying an input signal, a variable signal attenuator 1117 for adjusting the strength of the amplified signal, and a divider 1103 for dividing the attenuated signal into two paths. ), The components 1109, 1113, 1114, 1115, 1116, and 1110 of the error signal detection unit for detecting an error signal of the amplifier, the signal delay circuit unit 1119 in which the input signal changes linearly, and the error signal detection unit, respectively. Combiner that combines the signal output from the components and the signal output from the signal delay circuit unit 1119, the signal attenuator 1105 for changing the magnitude of the signal output from the combiner, and the signal output from the signal attenuator Since it is composed of a terminal amplifier 1106 for amplifying the same as the conventional linearizer (100 of FIG. 1), a detailed description thereof will be omitted.

The power amplifier 3000 amplifies the signal having the reduced distortion component in the linearizer 1000, and the second directional coupler separates the signal output from the power amplifier 3000 into two output signals.

The error signal detector 2000, which is a key component of the present invention, detects a change in amplification gain and phase by comparing a second signal separated from the first directional coupler with an output signal output from the second directional coupler. As shown in FIG. 3, the error signal detector includes a first limiter 2500 for normalizing the magnitude of the second signal, a second limiter 2600 for normalizing the magnitude of the output signal output from the second directional coupler; A first mixer detecting a gain error of the normalized signal and the second signal at the first limiter 2500, a second mixer detecting a gain error of the signal and the output signal normalized at the second limiter 2600; And a third mixer for detecting a phase error between the signal output from the first mixer and the signal output from the second mixer.

In addition, the power amplifier of the present invention attenuates the amplification gain of the output signal output from the second directional coupler as shown in FIG. 2 and adds an attenuator for applying the amplified gain attenuated output signal to the error signal detector 2000. It may also be configured to include.

Hereinafter, the operation principle of the power amplifier of the present invention will be described.

First, the signal input through the input port is separated by the first directional coupler. The first signal, which is one of the signals separated by the first directional coupler, is input to the linearizer 1000 through the variable attenuator 1102 and the variable phase transformer 1118 and amplified. Also, of the signals separated by the first directional coupler, the second signal is input to the error signal detector 2000.

At this time, the signal amplified by the linearizer 1000 generates a gain and a phase error according to a change in operating conditions of the power amplifier 3000. The method of detecting such a phase error is as follows.

First, the signal amplified by the linearizer 1000 is separated by the second directional coupler, input to the error signal detector 2000, and normalized by the second limiter 2600. In addition, the second signal inputted separately by the first directional coupler is normalized by the first limiter 2500. At this time, the signal normalized by the first limiter 2500 and the second inputted signal are input to the first mixer to output a signal having a DC component having a magnitude and frequency twice that of the second signal, and outputting a second limiter ( The signal normalized by 2600 and the signal amplified by the linearizer 1000 are input to the second mixer, and a signal having a DC component having a magnitude and frequency twice that of the signal amplified by the linearizer 1000 is output.

The signal of the DC component output by the first mixer and the second mixer is respectively detected by the OP amplifier 2200 and input to the variable attenuator 1102. As a result, a control voltage and a gain control voltage for controlling the variable attenuator 1102 are output.

In addition, the signals output by the first limiter 2500 and the second limiter 2600 are respectively input to the third mixer and output as signals of twice the phase error component and the second signal frequency, and are output from the third mixer. The received signal is input to the variable phase transformer 1118 via the low pass filter 2100. As a result, a control signal for controlling the variable phase displacement transformer 1118 is output.

As a result, the variable attenuator 1102 passes through the first mixer and the low pass filter 2400 of the error signal detector 2000 and the signal input to the OP amplifier 2200 and the second mixer and the low pass filter 2300. The output signal of the signal input to the amplifier 2200, that is, the gain control voltage is input to compensate for the distortion of the first signal, and the variable phase transformer 1118 is a low pass filter 2100 of the error signal detector 2000 The phase of the first signal is compensated by receiving the output control signal.

The power amplifier of the present invention can compensate for a change in gain and signal phase of a power amplifier which is changed by external environmental changes or changes in operating conditions, thereby reducing the distortion of the amplified signal.

Claims (3)

A first directional coupler that separates an input signal into two first signals and a second signal, A variable attenuator for gain compensation of power by the first signal separated from the first directional coupler, Variable phase displacement compensation, A linearizer for reducing distortion caused at the output of the power amplifier, A power amplifier for amplifying the signal output from the linearizer, A second directional coupler for separating the signal output from the power amplifier into two output signals, A first and second limiters for normalizing the second signal separated from the first directional coupler and the output signal output from the second directional coupler, respectively, and using the normalized signals and the signals before normalization, A power amplifier comprising an error signal detector for detecting a phase error. The method of claim 1, wherein the error signal detection unit A first limiter for normalizing the magnitude of the second signal, A second limiter for normalizing the magnitude of the output signal output from the second directional coupler; A first mixer for detecting a gain error between the normalized signal at the first limiter and the second signal; A second mixer for detecting a gain error between the normalized signal at the second limiter and the output signal; And a third mixer detecting a phase error between the signal output from the first mixer and the signal output from the second mixer. The power amplifier of claim 1, wherein the power amplifier And an attenuator for attenuating the amplification gain of the output signal output from the second directional coupler to apply the amplified gain attenuated output signal to the error signal detector.