JP2012015611A - High-power amplification circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-power amplification circuit capable of detecting a distorted component caused by an amplifier in a simple structure, and suppressing the distorted component at low cost and by low power consumption.SOLUTION: A high-power amplification circuit includes: an amplifier having linear amplification characteristics and amplifying an input signal, a center frequency of which is known, to output; a third order harmonic component extraction circuit extracting a third order harmonic component, in which a center frequency is three times as much as that of the input signal, out of harmonic components arising from an output signal of the amplifier due to non-linear amplification characteristics; and an envelope curve detection circuit detecting an envelope curve signal of the third order harmonic component from the output of the third order harmonic component extraction circuit. The high-power amplification circuit further includes a distorted component suppression circuit separating the input signal into a carrier signal and the envelope curve signal, generating a summation signal obtained by adding the envelope curve signal of the input signal and the envelope curve signal of the third order harmonic component, and multiplying this summation signal by the carrier signal of the input signal to input the product thereof into the amplifier.

Description

  The present invention relates to a high-power amplifier circuit that is used in radio communication equipment and the like, and particularly has high efficiency and high linearity.

  At present, in a high-power amplifier circuit used for high-frequency power amplification in the field of wireless communication equipment and the like, in order to achieve high efficiency and high linearity simultaneously, a feedback type (Non-Patent Document 1, Non-Patent Document 2) In some cases, a predistortion type (Non-Patent Document 3, Non-Patent Document 4) distortion compensation circuit is introduced.

FIG. 7 shows a configuration example of a conventional high-power amplifier circuit.
In FIG. 7, the conventional high output amplifier circuit branches the input signal and output signal of the amplifier 11 by couplers 21-1, 21-2 and inputs them to the detectors 22-1, 22-2, respectively. The comparator 23 compares the envelope power detected at -1,22-2. Since the output of the comparator 23 corresponds to the intensity of the distortion component generated in the amplifier 11, the distortion component suppression circuit 24 arranged in the previous stage of the amplifier 11 is controlled according to the intensity of the distortion component to control the nonlinear characteristic of the amplifier 11. Is compensated for and the distortion component is adaptively suppressed.

  The amplifier 11 is in a state where the input / output characteristics are suppressed in the previous stage of the saturation region, and this is detected as a distortion component. Therefore, when the intensity of the detected distortion component is large, by increasing the gain of the variable gain amplifier used as the distortion component suppression circuit 24, the linearity of the input / output characteristics is maintained until the amplifier 11 enters the saturation region, High efficiency is achieved by operating at low distortion near the saturation region.

  In addition, the predistortion type distortion compensation circuit using a distortion input circuit as the distortion component suppression circuit 24 is configured to suppress the distortion component by injecting an anti-phase component of distortion into the input signal of the amplifier 11, and the intensity of the distortion component. Accordingly, the distortion component is suppressed by adjusting the anti-phase component of the distortion to be injected.

T. Arthanayake, et. Al., “Linear amplification using envelope feedback,” IEEE Electronics Letters, vol.7, pp.145-146, April, 1971 Hiroaki Kosugi, et al., “Highly efficient linear power amplifier using envelope feedback control,” IEICE Transactions C-I, vol. J76-C-I, no.11, pp.407-413, 1993 Masayuki Adachi, et al., “Development of 7 GHz band power amplifier using analog predistortion,” Japan Radio Technical Report, No.51, 2006 J. Kathleen, et. Al., “Look-Up Table Techniques for Adaptive Digital Predistortion: A Development and Comparison,” IEEE Trans. On Vehicular Technology, vol.49, no.5, Sep., 2009

  In order to detect the intensity of the distortion component, the conventional high-power amplifier circuit has a configuration in which the input signal and the output signal are taken out via a coupler disposed before and after the amplifier and the respective envelope powers are compared. .

  Here, if the input signal and the output signal are similar, there is no distortion, and if it is not similar, it can be determined that there is distortion. However, when a distortion anti-phase component is simply injected into the input signal so as to be proportional to the amount of distortion, “no distortion → sets the distortion anti-phase component injection amount to zero → distortion generation → distortion anti-phase component It is assumed that the control operation is stabilized when the process of “increasing the injection amount → no distortion” is repeated or the distortion remains. In other words, control that simply injects the anti-phase component of distortion into the input signal so that it is proportional to the amount of distortion is not sufficient, and more sophisticated control is required, increasing the circuit scale of the high-power amplifier circuit. However, there has been a problem of increasing costs and increasing power consumption.

  An object of the present invention is to provide a high output amplifier circuit that can detect distortion components in an amplifier with a simple configuration and suppress distortion components at low cost and low power consumption.

  A high-power amplifier circuit according to a first aspect of the present invention includes an amplifier that has a nonlinear amplification characteristic and amplifies and outputs an input signal having a known center frequency, and a harmonic component generated by the nonlinear amplification characteristic from the output signal of the amplifier. The third harmonic component extraction circuit that extracts the third harmonic component whose center frequency is three times that of the input signal and the envelope signal of the third harmonic component are detected from the output of the third harmonic component extraction circuit. An envelope detection circuit and an input signal are separated into a carrier signal and an envelope signal, a sum signal is generated by adding the envelope signal of the input signal and the envelope signal of the third harmonic component, and this sum signal and input And a distortion component suppression circuit that multiplies the carrier signal of the signal and inputs it to the amplifier.

  A high-power amplifier circuit according to a second aspect of the invention has a non-linear amplification characteristic and a gain control function, a variable gain amplifier that amplifies and outputs an input signal having a known center frequency, and a non-linear amplification characteristic from the output signal of the variable gain amplifier 3rd harmonic component extraction circuit that extracts the 3rd harmonic component whose center frequency is 3 times that of the input signal, and 3rd harmonic from the output of the 3rd harmonic component extraction circuit. An envelope detection circuit for detecting an envelope signal of a component, an input signal is separated into a carrier signal and an envelope signal, the carrier signal of the input signal is input to a variable gain amplifier, and the envelope signal and the third harmonic of the input signal are input A distortion signal suppression circuit is provided that generates a sum signal obtained by adding the envelope signal of the wave component and controls the gain of the variable gain amplifier based on the sum signal.

  In the high output amplifier circuit of the first invention, the sum signal amplitude is a value obtained by multiplying the ratio of the third harmonic distortion voltage gain of the amplifier to the fundamental voltage gain by −3/4 with respect to the cube of the input signal. The configuration is as follows.

  In the high output amplifier circuit of the first invention, the sum signal amplitude is obtained by multiplying the third power of the input signal by -3/2 to the ratio of the third harmonic distortion voltage gain of the amplifier to the fundamental voltage gain. It is the composition which makes the value which does not exceed.

  In the high output amplifier circuit of the second invention, the sum signal amplitude is multiplied by -3/4 to the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the variable gain amplifier to the cube of the input signal. It is the composition which makes it a value.

  In the high output amplifier circuit of the second invention, the sum signal amplitude is multiplied by -3/2 to the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the variable gain amplifier to the cube of the input signal. The value is set so as not to exceed the specified value.

  The high output amplifier circuit of the present invention easily detects the magnitude of the distortion component by extracting the third harmonic component generated by the amplifier from the output signal of the amplifier, and the distortion component is detected according to the intensity of the distortion component. Can be suppressed. As a result, a high-power amplifier circuit with a small circuit scale, low cost and low power consumption can be configured.

  Here, the extracted third harmonic component is proportional to the magnitude of distortion at the fundamental frequency when predistortion is not performed, and the magnitude of the third harmonic component does not change even if predistortion is performed. . Therefore, distortion can be compensated by simple control of performing predistortion proportional to the third-order harmonic component to be extracted. Also, since the sum signal obtained by adding the envelope signal of the input signal and the envelope signal of the third harmonic component and the carrier signal are multiplied, or the sum signal is used for gain control of the carrier signal, the carrier signal becomes a high frequency. However, it is not necessary to consider the phase adjustment of the carrier signal.

It is a figure which shows the structural example of Example 1 of the high output amplifier circuit of this invention. 3 is a diagram illustrating a frequency spectrum of an output signal of an amplifier 11. FIG. It is a figure which shows the structural example of Example 2 of the high output amplifier circuit of this invention. It is a figure which shows the structural example of Example 3 of the high output amplifier circuit of this invention. It is a figure which shows the structural example of Example 4 of the high output amplifier circuit of this invention. It is a figure which shows the structural example of Example 5 of the high output amplifier circuit of this invention. It is a figure which shows the structural example of the conventional high output amplifier circuit.

FIG. 1 shows a configuration example of Example 1 of a high-output amplifier circuit according to the present invention.
In FIG. 1, in the high-power amplifier circuit according to the first embodiment, a distortion component suppression circuit 12 is disposed in the front stage of the amplifier 11, and a third harmonic component extraction circuit 13 is disposed in the subsequent stage, and the third harmonic component extraction circuit 13. The third harmonic component is extracted from the output signal of the amplifier 11 and input to the envelope detection circuit 14. The envelope detection circuit 14 detects the envelope signal of the third harmonic component and inputs it to the distortion component suppression circuit 12 as the distortion component intensity of the output signal of the amplifier 11.

  The distortion component suppression circuit 12 includes a coupler 121 that divides an input signal into two, an envelope detection circuit 122 that detects an envelope signal from one input signal, and a limiter 123 that extracts a carrier signal from the other input signal. And the envelope signal of the input signal output from the envelope detection circuit 122 and the envelope signal (distortion component strength) of the third harmonic component output from the envelope detection circuit 14 in an opposite phase. Line adder 124, mixer 125 that multiplies the envelope signal output from envelope adder 124 with the distortion component suppressed and the carrier signal of the input signal output from limiter 123 to obtain the input signal of amplifier 11. Consists of.

  The feature of this embodiment is that the intensity of the distortion component of the amplifier 11 is detected from the third harmonic component extracted from the output signal of the amplifier 11, and the distortion component is added to the envelope signal of the input signal to suppress distortion. There is a place to do. Whereas a conventional high-power amplifier circuit has a configuration in which couplers are arranged before and after the amplifier 11 and the envelope strengths of the branched input signal and output signal are compared to detect the strength of the distortion component, In the present embodiment, the envelope signal (distortion component intensity) is detected from the third harmonic component extracted by the third harmonic component extraction circuit 13 arranged at the subsequent stage of the amplifier 11, and the circuit scale can be reduced. It is possible.

  Hereinafter, the principle by which the intensity of the distortion component can be estimated from the third harmonic component of the output signal of the amplifier 11 will be described.

The simple input / output characteristics of the amplifier 11 are as follows: the input signal is X, the output signal is Y, the fundamental voltage gain, the second harmonic voltage gain, the third harmonic voltage gain (third harmonic distortion voltage gain), which are eigenvalues of the amplifier 11 ) As a ₁ , a ₂ , and a ₃ , respectively, can be approximately expressed by the following polynomial.
Y = a ₁ X + a ₂ X ² + a ₃ X ³ (1)

Here, assuming a modulation signal as the input signal X,
X = s (t) cos (ω _c t)
It becomes. ω _c is the angular frequency of the input signal, and t is time. The output signal Y is expressed separately for each frequency component to be generated.
DC component: Y _DC = (1/2) a ₂ s (t) ² (2)
Fundamental wave component: Y _1st = (a ₁ s (t) + (3/4) a ₃ s (t) ³ ) cos (ω _c t) (3)
Second harmonic component: Y _2nd = (1/2) a ₂ s (t) ² cos (2ω _c t) (4)
Third harmonic component: Y _3rd = (1/4) a ₃ s (t) ³ cos (3ω _c t) (5)
It becomes.

The frequency spectrum of the output signal of the amplifier 11 is shown in FIG. A distortion component 102 generated around the desired signal 101 is a signal to be suppressed. The distortion component 102 has the same frequency band and envelope as the third harmonic component 103. When the envelope of the third harmonic component 103 is extracted and added to the envelope on the input side, the input signal to the amplifier 11 is
X′≈ (s (t) + B × s (t) ³ ) cos (ω _c t) (6)
It becomes. Here, B is a constant derived from the gain of the feedback system. Substituting into equation (1) and summing up the fundamental wave component and third harmonic component,
Fundamental wave component:
Y _1st = a ₁ s (t) cos (ω _c t) + (3/4) a ₃ s (t) ³ cos (ω _c t)
{A ₁ s (t) ³ B + (3/4) a ₃ (3s (t) ⁵ B + 3 s (t) ⁷ B ² + s (t) ⁹ B ³ )} cos (ω _c t)
… (7)
Third harmonic component: Y _3rd = (1/4) a ₃ {s (t) ³ + 3s (t) ⁵ B + 3s (t) ⁷ B ² + s (t) ⁹ B ³ )} cos (3ω _c t)
… (8)
It becomes.

Looking at the fundamental wave component, the first term is the desired signal, the second term is the distortion generated before compensation, and the third term is the signal that is generated by returning the third harmonic envelope to the input. It is. Here, in the third term, the input signal s (t) of the amplifier is sufficiently small with respect to the output signal. Therefore, if the higher order components after s (t) ⁵ are ignored, the second and third terms To remove the distortion component,
(3/4) a ₃ s (t) ³ + a ₁ s (t) ³ B = 0 (9)
Should be satisfied. That is,
B =-(3/4) a ₃ / a ₁ (10)
It becomes.

  As described above, the third-order distortion that occurs can be canceled by returning the envelope signal of the third-order harmonic component to the input with a constant gain B. This signal can also be created by inverting the phase of the envelope. The gain B can also be set by the envelope adder 124.

Further, the intensity is less than twice the optimum value of gain B shown in equation (10), that is, 0>B> − (3/2) a ₃ / a ₁ (11)
If so, the effect of reducing the distortion is more effective than when no compensation is performed.

  Further, from equation (8), it can be seen that even if the envelope signal of the third harmonic component is returned to the input, the third harmonic component does not change if s (t) is sufficiently small. For this reason, the envelope signal amount fed back continues even after the distortion is corrected, and the distortion is always automatically corrected while the distortion is occurring.

  The third-order harmonic extraction circuit 13 branches the output signal of the amplifier 11 by a branching means 131 such as a power distributor or a coupler, and a third-order harmonic is output from the branched output signal by a filter 132 such as a bandpass filter or a highpass filter. It is realizable by the structure which extracts a component. At this time, harmonics are cut by installing a filter 133 that transmits the same center frequency as the center frequency of the input signal and does not transmit the second and higher harmonics of the input signal on the output side of the high-power amplifier circuit. It becomes possible.

  The third harmonic extraction circuit 13 uses a branching filter that demultiplexes the output signal of the amplifier 11 into a fundamental wave component and a third harmonic component, and uses the fundamental wave component as an output of the high-power amplifier circuit. The third harmonic component may be input to the envelope detection circuit 14. In such a duplexer, one of the two output ports has a low impedance with respect to the third harmonic component (high impedance with respect to the fundamental wave component and the second harmonic component), and the other has a third harmonic component. On the other hand, the one designed to have high impedance (low impedance with respect to the fundamental wave component) is used.

FIG. 3 shows a configuration example of Embodiment 2 of the high-output amplifier circuit of the present invention.
3 is the same as the first embodiment except that an operational amplifier (differential amplifier circuit) 126 is used instead of the envelope adder 124 of the first embodiment. By configuring the envelope adder 124 with the operational amplifier 126, the value of the gain B can be adjusted and changed flexibly.

FIG. 4 shows an example of the configuration of Embodiment 3 of the high-power amplifier circuit according to the present invention.
In FIG. 4, a digital EER circuit 127 is used instead of the coupler 121, the envelope detection circuit 122, and the limiter 123 of the second embodiment, and the input signal is separated into an envelope signal, a phase signal, and a carrier signal by the digital EER circuit 127. Of these, the phase signal and the carrier signal are input to the mixer 128, and the output signal of the mixer 128 is input to the mixer 135. Other configurations are the same as those of the second embodiment. With such a configuration, the digital EER circuit 127 can be used.

FIG. 5 shows a configuration example of Embodiment 4 of the high-output amplifier circuit of the present invention.
5 is the same as the second embodiment except that the variable gain amplifier 15 is used instead of the amplifier 11 of the second embodiment and the function of the mixer 125 is provided in the variable gain amplifier 15. That is, when the carrier signal of the input signal output from the limiter 123 is amplified by the variable gain amplifier 15, the gain is controlled by the envelope signal output from the operational amplifier (envelope adder) 126. 15 can have the function of the mixer 125. With such a configuration, the number of parts can be reduced.

FIG. 6 shows an example of the configuration of Embodiment 5 of the high-output amplifier circuit according to the present invention.
In FIG. 6, a digital EER circuit 127 is used instead of the coupler 121, the envelope detection circuit 122, and the limiter 123 of the fourth embodiment, and the input signal is separated into an envelope signal, a phase signal, and a carrier signal by the digital EER circuit 127. Of these, the phase signal and the carrier signal are input to the mixer 128, and the output signal of the mixer 128 is input to the variable gain amplifier 15. Other configurations are the same as those in the fourth embodiment. With such a configuration, the digital EER circuit 127 can be used.

DESCRIPTION OF SYMBOLS 11 Amplifier 12 Distortion component suppression circuit 121 Coupler 122 Envelope detection circuit 123 Limiter 124 Envelope adder 125,128 Mixer 126 Operational amplifier 127 Digital EER circuit 13 Third harmonic extraction circuit 131 Branch means 132, 133 Filter 14 Envelope detection Circuit 15 Variable gain amplifier 21 Coupler 22 Detector 23 Comparator 24 Distortion component suppression circuit

Claims (6)

An amplifier that has nonlinear amplification characteristics and amplifies and outputs an input signal having a known center frequency;
A third-order harmonic component extraction circuit that extracts a third-order harmonic component having a center frequency three times that of the input signal among the harmonic components generated by the nonlinear amplification characteristic from the output signal of the amplifier;
An envelope detection circuit for detecting an envelope signal of the third harmonic component from the output of the third harmonic component extraction circuit;
The input signal is separated into a carrier signal and an envelope signal, a sum signal is generated by adding the envelope signal of the input signal and the envelope signal of the third harmonic component, and the sum signal and the carrier signal of the input signal are generated. And a distortion component suppression circuit that multiplies and inputs to the amplifier. A variable gain amplifier having a non-linear amplification characteristic and a gain control function, and amplifying and outputting an input signal having a known center frequency;
A third-order harmonic component extraction circuit for extracting a third-order harmonic component having a center frequency three times that of the input signal among the harmonic components generated by the nonlinear amplification characteristic from the output signal of the variable gain amplifier;
An envelope detection circuit for detecting an envelope signal of the third harmonic component from the output of the third harmonic component extraction circuit;
The input signal is separated into a carrier signal and an envelope signal, the carrier signal of the input signal is input to the variable gain amplifier, and the sum of the envelope signal of the input signal and the envelope signal of the third harmonic component is added And a distortion component suppression circuit that generates a signal and controls the gain of the variable gain amplifier based on the sum signal. The high-power amplifier circuit according to claim 1,
The amplitude of the sum signal is a value obtained by multiplying the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the amplifier by -3/4 to the cube of the input signal. Output amplifier circuit. The high-power amplifier circuit according to claim 1,
The amplitude of the sum signal should not exceed a value obtained by multiplying the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the amplifier by −3/2 with respect to the cube of the input signal. High-output amplifier circuit that is characterized. The high output amplifier circuit according to claim 2,
The sum signal amplitude is obtained by multiplying the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the variable gain amplifier by -3/4 to the cube of the input signal. High output amplifier circuit. The high output amplifier circuit according to claim 2,
The amplitude of the sum signal does not exceed a value obtained by multiplying the ratio of the third harmonic distortion voltage gain and the fundamental voltage gain of the variable gain amplifier by −3/2 with respect to the cube of the input signal. A high-power amplifier circuit characterized by that.

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