JPH03254211A - Nonlinear distortion compensation circuit for high output amplifier - Google Patents

Abstract

PURPOSE:To expand a permissible range with respect to feedback delay and to save a storage area at waveform control by separating a nonlinear distortion from the output of a high output amplifier through the use of, e.g. a filter depending on the degree, and feeding back nonlinear distortion from a distortion extraction circuit for each degree negatively to the distortion for each degree from a distortion generating circuit and synthesizing the result. CONSTITUTION:A nonlinear distortion for each degree from a distortion extraction circuit 4 is fed back negatively to a distortion for each degree from a distortion generating circuit 6 to synthesize them and a synthesis signal is outputted from a synthesis circuit 7 to a high output amplifier 1. The distortion extraction circuit 4 separates the nonlinear distortion from the output of the high output amplifier 1 for each degree and a filter 41-i (i is a natural number) separating nonlinear distortion for each degree from an output of the high output amplifier 1 is provided to the distortion extraction circuit 4. Moreover, the distortion generating circuit 6 is a circuit to generate (2i+1)th distortion (i is a natural number) from a base band signal. Then a modulator 8 modulates a signal from the synthesizing circuit 7 and outputs the result to the high output amplifier 1. Thus, the permissible range to the feedback delay is expanded and the storage area at the time of controlling the waveform is saved.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Fig. 11) Means for solving the problem to be solved by the invention (Fig. 1) Effect (Fig. 1) ) Embodiments (Figures 2 to 10) Effects of the invention [Summary] Regarding a nonlinear distortion compensation circuit for a high output amplifier that compensates for nonlinear distortion of a high output amplifier provided on the transmitting side, the tolerance range for feedback delay is expanded and the tolerance range for feedback delay is expanded. , with the aim of reducing the storage area during waveform control, and in order to give the input signal to the high-output amplifier a distortion that has the opposite characteristics to the distortion of the high-output amplifier, the baseband signal is converted to 2i + 1st order. A distortion generation circuit that generates distortion, a distortion extraction circuit that separates nonlinear distortion for each order from the output of a high-output amplifier, and a distortion extraction circuit that separates the nonlinear distortion for each order from the distortion generation circuit and the nonlinear distortion for each order from the distortion extraction circuit. It is configured to include a combining circuit that feeds back and combines the signals and outputs the combined signal to the high-output amplifier side.

[Industrial Field of Application] The present invention relates to a nonlinear distortion compensation circuit for a high output amplifier that compensates for nonlinear distortion of a high output amplifier (high power amplifier) provided on a transmitting side.

[Prior Art] Fig. 11 is a block diagram of a conventional nonlinear distortion compensation circuit for a high-output amplifier. In Fig. 11, 100 is a high-output amplifier, and this high-output amplifier 100 has nonlinear distortion. ing. That is, when a signal is input to this high-output amplifier 100, it is distorted and output.

101 is a directional coupler, and this directional coupler 101 is
A part of the output of the high output amplifier 100 is taken out.

102 is a demodulator, and this demodulator 102 demodulates a part of the output of the high-power amplifier 100 taken out by the directional coupler 101.

103 is a deviation calculator, and this deviation calculator 103 calculates the deviation between the output U of the demodulator 102 and the baseband signal V.

104 is a storage unit, and this storage unit 104 is used for the deviation calculator 1.
It stores deviation information from 03, for example, RA
M is used.

105 is a combiner, and this combiner 105 combines the baseband signal V and the deviation information from the storage unit 104 in a negative feedback state.

106 is a variable am, and this modulator 106 is 1 combiner 105
The signal is modulated and input to the high output amplifier 100.

With this configuration, in order to compensate for nonlinear distortion of the high-output amplifier 100, the input signal V and the demodulator output signal U are compared in the deviation calculator 103, and a deviation signal (uv) is generated.
is negatively fed back to the input signal V. The feedback amount at this time is stored in the storage section 104, and the data in the storage section 104 is added to the input signal V. Note that the data stored in the storage unit 104 is updated each time data is transmitted.

In this way, the input signal %v is successively increased to the high power amplifier 1
00, and nonlinear compensation is applied.

[Problems to be Solved by the Invention] However, in such conventional nonlinear distortion compensation circuits for high-output amplifiers, since the time waveform is directly controlled,
If there is a delay time in the feedback loop of the circuit shown in the figure, a change in the demodulator output U due to the time lag directly becomes a waveform control error. Therefore, it is necessary to make the delay time in the feedback loop zero or to accurately estimate it to perform time adjustment. Here, the higher the required accuracy for distortion compensation, the narrower the allowable range for this time adjustment.

In addition, in order to achieve high-precision distortion compensation, waveform control must be accurate, so the above input signal V and demodulator output U
should be digital data with many bits, and it is necessary to store waveform control information for each value of the baseband signal in the RAM of the storage unit 104. - For example, when transmitting a QPSK signal: - If each of the I and Q channels is 10-bit data, the input signal value is 1
Since there are 024 x 1024 combinations and it is necessary to store 10 bit data for all of them, the storage area required for this is as much as 10 Mbit. With such a large RAM area, its power consumption cannot be ignored, and furthermore, there is a problem in that this power consumption substantially reduces the efficiency of the high-power amplifier 100.

The present invention has been made in view of these problems, and provides a nonlinear distortion compensation circuit for high-output amplifiers that expands the tolerance range for feedback delay and reduces the storage area during waveform control. It is intended to.

[Means for Solving the Problems] FIG. 1 is a block diagram of the principle of the present invention (corresponding to claim 1).

In FIG. 1, 1 is a high output amplifier, and this high output amplifier 1 has nonlinear distortion. That is, when a signal is input to this high-output amplifier 1, it is distorted and output.

Reference numeral 2 denotes a signal extraction section, and this signal extraction section 2 extracts a part of the output of the high-output amplifier l.

3 is a demodulator, and this demodulator 3 demodulates a part of the output of the high-output amplifier 1 extracted by the signal extraction section 2.

Reference numeral 4 denotes a distortion extraction circuit, and this distortion extraction circuit 4 separates nonlinear distortion from the output of the high-output amplifier 1 for each order. It has a filter 4l-i (i is a natural number) that separates distortion by order.

6 is a distortion generation circuit, and this distortion generation circuit 6 generates 2i+1st-order distortion (i is a natural number) from the baseband signal.

7 is a synthesis circuit, which synthesizes the distortion for each order from the distortion generation circuit 6 by negative feedback of the nonlinear distortion for each order from the distortion extraction circuit 1Ir4, and sends this synthesized signal to the high output amplifier 1. It is output to the side.

8 is a modulator, and this modulator 8 modulates the signal from the combining circuit 7 and inputs it to the high output amplifier 1.

In this way, the input signal to the high-output amplifier 1 can be given a distortion having characteristics opposite to the distortion of the high-output amplifier l.

[Function] In the above-mentioned nonlinear distortion compensation circuit for a high-output amplifier of the present invention (as claimed in claim 1), in the signal extraction section 2.

A part of the output of the high-power amplifier 1 is taken out and demodulated by a demodulator 3, and then a distortion extraction circuit 4 separates nonlinear distortion from the output of the high-power amplifier 1 for each order. At this time, in the second aspect of the present invention, a filter is used to separate the nonlinear distortion for each order.

On the other hand, the distortion generation circuit 6 uses 2i based on the baseband signal.
+1st-order distortion is generated, and in the synthesis circuit 7, the nonlinear distortion for each order from the distortion extraction circuit 4 is negatively fed back to the distortion for each order from the distortion generation circuit 6, and synthesized. .

Thereafter, the modulator 8 modulates the signal from the combining circuit 7 and inputs the modulated signal to the high output amplifier 1.

Thereby, the input signal to the high-output amplifier 1 can be given a distortion having characteristics opposite to the distortion of the high-output amplifier 1.

[Example code] The present invention will be described in detail below with reference to one drawing.

The second @ is a block diagram showing one embodiment of the present invention,
The nonlinear distortion compensation circuit for high output amplifier according to this example is as follows:
As shown in FIG. 2, a high power amplifier 1. Directional coupler as a signal extraction section 2. Demodulator 3. Distortion extraction circuit 4. Memory circuit 5. Distortion generation circuit 6° synthesis circuit 7. It is equipped with a modulator 8.

Here, the high-output amplifier 1 has nonlinear distortion, and therefore, when a signal is input to this high-output amplifier 1, it is outputted with distortion.

The directional coupler 2 takes out a part of the output of the high-output amplifier 1, and the demodulator 3 demodulates part of the output of the high-output amplifier 1 taken out by the directional coupler 2. Note that a down converter can also be used instead of this demodulator 3.

The distortion extraction circuit 4 separates nonlinear distortion from the output of the high-output amplifier 1 for each order (2i + 1st order), and for this purpose, the distortion extraction circuit 4 separates nonlinear distortion from the output of the high-output amplifier 1 by 1 (=n) as shown in FIG. I
I filter 41-1 to 4l-n9 multiplier 42-0.4
2-1 to 42-n, polarity inverter 432 divider 44-1 to
44-n.

The filters 41-1 to 41-n are 3, 5 .・・2n
It extracts +1st-order distortion, and uses a bandpass filter or a bypass filter.

For example, the passbands of filters 41-1 and 41-2 are shown in FIG. From this, the third-order distortion is extracted by the filter 41-1, and the third-order distortion is extracted by the filter 41-2.
It can be seen that fifth-order distortion is extracted.

The multiplier 42-O obtains the autocorrelation output A0 of the demodulator output U, and the multipliers 42-1 to 42-n obtain the autocorrelation outputs A1 to An of the outputs of the filters 41-1 to 41-n, respectively.
By taking the autocorrelation in this way, nonlinear distortion can be extracted regardless of the feedback delay.

The polarity inverter 43 is the output A of the 1 multiplier 42-O.

This is to invert the polarity of the signal and perform processing to create a negative feedback state.

Dividers 44-1 to 44-n are multipliers 42-1 to 42-n.
By dividing the output A□~An of -n by the output -A0 of the polarity inverter 43, the regular catering car A/A, ~ -A n
/A, is obtained. And these regular catering cars A/A, ~-A n/A.

has weight information.

The storage circuit 5 stores the nonlinear distortion -A1/A for each order obtained by the distortion extraction circuit 4, in order to give the input signal to the high-output amplifier 1 a distortion having characteristics opposite to the distortion of the high-output amplifier 1.
~-A n/A (1) This storage circuit 5 includes a rewritable memory (RAM) so that the nonlinear distortion for each order can be updated.

The distortion generation circuit 6 generates a baseband signal V (this signal V is Q
I and Q channel signals VI of quadrature modulation signals in PSK
consisting of eVQ) from 3,5. . . 2n+1st-order distortion is generated, and as shown in FIG. 4, this distortion generation circuit 6 is equipped with an adder 1i 161 and a large number of multipliers 62 for calculating the correlation of signals.

By the way, the nonlinear distortion of the high-output amplifier 1 is caused by gain saturation and AM
/PM conversions, which are a function of the input power level. Therefore, when complex representation is used, the baseband signal V becomes vl+jvo, so the third-order nonlinearity is represented by (vv lines)v, and the fifth-order nonlinearity is expressed as (vv*
)”v. Note that the seven numbers are the conjugate complex numbers of V.

Here, an example of a circuit for generating 3rd and 5th order distortion is shown in FIG. This circuit is also configured by combining an adder s61 and a multiplier 62, but in this circuit, V
After adding up each autocorrelation of IyVQ, add VI to this result.
By multiplying by yVQ, third-order nonlinear distortion is generated, and autocorrelation is taken for (vv lines), and V
By multiplying by IyVQ, fifth-order nonlinear distortion is generated.

Note that (vv lines) Vxt (VV'') Vo are added to both the I and Q channels, and (vv lines) VI is added to the ■ channel to compensate for the third-order component of gain saturation, and (vv
*) When adding vx to the Q channel, 3 of AM/PM conversion
Contributes to compensation of next component.

Of course, after the 5th, 7. ..., 2n+1st-order nonlinear distortion can be obtained in a similar manner.

The synthesizing circuit 7 negative-feeds back and synthesizes the distortion for each order from the distortion generation circuit 6 and the nonlinear distortion for each order from the storage circuit 5, and outputs this composite signal to the high-output amplifier 1 side.
For this purpose, an addition circuit 71 consisting of n adders 711-1 to 711-n.

A combining/adding circuit 72 is provided for combining and adding the distortion compensation signals for each of the n orders from the adding circuit 71.

Then, the above memory circuit 5. Distortion generation circuit 62 synthesis circuit 7
A predistorter PD is configured.

The modulator 8 modulates the signal from the combining circuit 7 and inputs the modulated signal to the high output amplifier 1. Note that an up-converter may be used instead of this modulator 8.

With the above configuration, the directional coupler 2 connects the high output amplifier 1
A part of the output is extracted and demodulated by a demodulator 3, and then a distortion extraction circuit 4 separates nonlinear distortion from the output of the high-power amplifier 1 for each order. The nonlinear distortion thus extracted is stored in the storage circuit 5. Note that the data stored in this storage circuit 5 is updated each time data is transmitted.

On the other hand, the distortion generation circuit 6 uses 3
~b In the circuit 7, for each order distortion from this distortion generation circuit 6,
The nonlinear distortion of each order from the distortion extraction circuit 4 is negatively fed back and synthesized.

Thereafter, the modulator 8 modulates the signal from the combining circuit 7 and inputs the modulated signal to the high output amplifier 1.

Thereby, the input signal to the high-output amplifier 1 can be given a distortion having characteristics opposite to the distortion of the high-output amplifier 1.

In this way, by correlating each output of the distortion extraction circuit 4 with the distortion signal generated by the distortion generation circuit 6.

Delay tolerance is significantly improved. In order to quantitatively compare this point, a computer simulation was performed on the suppression effect of intermodulation distortion, and the results of evaluating the allowable range for the delay time are shown in FIG. 7. The one in FIG. 7 compensates for nonlinearities up to the fifth order, and it can be seen from this figure that the tolerance range for delay is larger than in the conventional one.

In addition, the information necessary for waveform control is only the coefficients when nonlinearity is expressed as a power series, and if nonlinear distortion is created for each order with the predistorter PD as described above, the information storage is A small area is sufficient. For example, when compensating for nonlinear distortion up to the 5th order, only the ratio of the 3rd and 5th order coefficients to the 1st order is sufficient. However, since the nonlinear distortion of the high-output amplifier 1 includes gain saturation and AM/PM conversion as described above, two pieces of information are required for each order.

Therefore, in this case, four pieces of information are sufficient. This makes it possible to significantly reduce the storage area required for waveform control.

Note that in the above embodiment, the autocorrelation A of the demodulator output U. is added to the RAM of the storage circuit 5 as a linear component weight, and the polarity of the autocorrelation A1 of each filter 41-1 is inverted,
It is also possible to add to the RAM of the storage circuit 5 without performing division.

In addition, each output of the filter 41-i and 2i of the distortion generation circuit 6
These may be multiplied by the +1st-order component and fed back to the predistorter PD. In this case, it is possible to implement either the above-mentioned division method or no division method.

By the way, the relationship between the baseband signal V (V + jvc +) and the demodulator output u (ux + j uo) is as follows:
A distortion wk is created for each order.

Here, wk is as follows.

wk= (vv*) v (k=1.2. #・)
(2) Here, since the above-mentioned Ak has extracted distortion component information for each order, if this Ak can be determined, the circuit for determining this constitutes the distortion extraction circuit 4.

A method for obtaining an approximate value of Ak using the above signals U and V will be described below.

First, in order to obtain an approximate value of A, it is sufficient to find the time average (uv*) of uv pieces, and from U, <uv*>
The linear component can be removed from U by subtracting v/(vv*). Here, in order to avoid division, p=(vv book>u-<uv book>V... (3). A circuit for doing this is shown in FIG. 8.

This figure is complicated because it faithfully represents the actual DSP processing, but if it is simplified using blocks, it becomes as shown in FIG. 9.

That is, as shown in FIGS. 8 and 9, this circuit has delay line 1
0,11. Multipliers 12-14. Integrator 15.16. It is configured with a subtracter 17.

Here, the delay line 10 delays the signal U by the calculation time of the integrator 15, and the delay line 11 delays the signal V by the calculation time of the integrator 15.
3. It is delayed by the calculation time of the integrator 16, and actually exists for the I and Q channels.

The integrator 15 performs time integration on v v * (= vz''+vg''), and the result <vv*> is input to the multiplier 12 .

The multiplier 12 multiplies (v v *) information from the integrator 15 and the signal U to output (vv *) u, but multiplies the I and Q channel components of the signal U. In order to perform this, it has a plurality of multipliers 12i.

The multiplier 13 multiplies the signals v and u* (u* is the complex conjugate of U) and outputs uv*.

A plurality of multipliers 131 . Adder 132. A subtracter 133 is provided. Note that the output of the adder 132 is 07 real parts Re (uv*), and the output of the subtracter 133 is 07 imaginary parts Im (uv).

The integrator 16 performs time integration on the output of the multiplier 13, and since the output of the multiplier 13 has a real part and an imaginary part, two integrators 161 are provided. and,
The outputs (97 outputs) of this integrator 16 can be taken out as linear components.

The multiplier 14 multiplies the (uv pieces) information from the integrator 16 and the signal V and outputs (uv pieces). However, it multiplies the I and Q channel components of each signal. For this purpose, a plurality of multipliers 141, adders 142, and subtracters 143 are provided.

The subtracter 17 subtracts the output (uv*)v of the multiplier 14 from the output (vv*)u of the multiplier 12, and in this case, I
, a plurality of subtracters 17 to perform calculations for Q channels.
1, and the subtracter 17 outputs p (p?PQ) as shown in equation (3) above.

Furthermore, the linear components (97) extracted in FIGS. 8 and 9 are as follows.

As<vv*) ・ ・ ・ ・ (4) In addition, in order to extract the nonlinear distortion components in order from the lowest order, wk generated by the distortion generation circuit 6 is expressed as f(1)k ・ ・ (5) By creating this, the P created in Figures 8 and 9 becomes,
A circuit for creating this f(1)k is shown in FIG.

The circuit shown in FIG. 10 is a circuit for realizing equation (5), and for this purpose, delay lines 18, 19 . Integrator 20, 2i
．． Multipliers 22, 23. It is equipped with a subtracter 24. That is, after 77 signals are time-integrated by the integrator 2i,
This is multiplied by the signal ■ delayed by the integral calculation time at 8 in the delay line 19 in the multiplier 22, and in the subtracter 24,
The output of multiplier 22 is subtracted from the output of multiplier 23. As a result, f(1)k is obtained.

In FIG. 9.10, the lines necessary for the I and Q channels are drawn as double lines.

Here, if the nonlinear distortion generated by the distortion generating circuit 6 is set to the 2n+1st order (compensation is performed to the 2n+1st order), n circuits having the same shape as that shown in FIG. 10 are required. However, k of each circuit is from 1 to n
becomes. That is, it is necessary to create from f(1) to f(1)n.

Note that the circuit for determining the third-order coefficient A1 from p is completely the same as that in FIGS. 8 and 9, and has inputs u and v*.

Instead of vv books, each P v f(1)i *y
f(1), f(1)□ books may be used. At this time, P
Instead, we obtain ql defined by the following equation.

However, after f(2)k is time-integrated by the divider 20, it becomes the delay line 1f(2
)k= <f(1)tf(IL*>f(L)k-<
f(1)kf(1), *>f(1).

・(8), and this f(2)k is replaced by (v
If we input the tree f(1)kf(1) instead of v*), we can obtain it as an output. In addition, < p f (1), tree> obtained here can be used to configure a distortion extraction port Mt4 including a filter by providing a required number of paths.

As described above, according to this embodiment, since the nonlinear distortion is separated for each order from the output of the high-power amplifier,
In addition to expanding the tolerance range for feedback delay, the nonlinear distortion for each order from the distortion extraction circuit is negatively fed back and synthesized with the distortion for each order from the distortion generation circuit, so it is possible to The storage area can be reduced.

NiA<f(1)□f(1)□Thu> (9), and an approximate value of 〇 is obtained for the third-order coefficient.

Furthermore, in the same manner as above, by simply changing the input, the AntA 1. A2
y...yAn can be determined.

Ai obtained in this way is stored in the RAM of the storage circuit 5, and then the distortion signal w from the distortion generation circuit 6 is
k and are combined and added in a negative feedback state.

It is input to the high output amplifier 1.

Therefore, the simple circuit shown in FIGS. 8 and 9 above [Effects of the Invention] As detailed above, according to the nonlinear distortion compensation circuit for a high-output amplifier (claim 1) of the present invention, the nonlinear distortion compensation circuit for a high-output amplifier Since nonlinear distortion is separated from the output by order using a filter (claim 2), the tolerance range for feedback delay can be expanded, and the distortion of each order from the distortion generation circuit can be separated. Since the nonlinear distortion of each order from the distortion extraction circuit is negatively fed back and synthesized,
This has the advantage of reducing the storage area during waveform control.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the principle of the present invention; Fig. 2 is a block diagram showing an embodiment of the invention; Fig. 3 is a block diagram showing a distortion extraction circuit as an embodiment of the invention; Each figure is a block diagram showing a distortion generation circuit as an embodiment of the present invention, and FIG. 6 is a diagram illustrating a pass band of a filter. Figure 7 is a diagram comparing the conventional and the present invention regarding the allowable range of delay time. Figures 8 and 9 are both circuits for extracting and removing linear components. Figure 10 is a conversion circuit for nonlinear elements. , FIG. 11 is a block diagram showing a conventional example. In the figure, 1 is a high output amplifier, 2 is a directional coupler (signal extraction section), 3 is a demodulator, and 4 is a distortion extraction circuit. 5 is a storage circuit, 6 is a distortion generation circuit, 7 is a synthesis circuit, 8 is a modulator, 10.11 is a delay line, 12 to 14 are multipliers, 15.16 is an integrator, 17 is a subtracter, 18.19 is a delay line, 20.2i is an integrator, 22.23 is a multiplier, 24 is a subtracter, 41-1 is a filter, 42-0.42-i is a multiplier, 43 is a polarity inverter, 44-1 is a 61 is an adder, 62 is a multiplier, 1 is an addition circuit. 2 is a synthesis adder circuit, and OO is a high output amplifier. 01 is a directional coupler, 02 is a demodulator, 03 is a deviation calculator, 04 is a storage unit, and 05 is a combination unit. 2i to 141 are multipliers, 61 is an integrator, and 71 is a subtracter. 11-1 is an adder. D is Bridaystoke.

Claims (1)

[Claims] (1) In a high-output amplifier nonlinear distortion compensation circuit that compensates for nonlinear distortion of a high-output amplifier (1), the input signal to the high-output amplifier (1) has characteristics opposite to the distortion of the high-output amplifier. A distortion generation circuit (6) that generates 2i+1st-order distortion (i is a natural number) from the baseband signal in order to provide distortion, and a distortion extraction circuit (6) that separates nonlinear distortion for each order from the output of the high-power amplifier (1). 4) and the distortion for each order from the distortion generation circuit (6) by negative feedback of the nonlinear distortion for each order from the distortion extraction circuit (4), and the combined signal is sent to the high output amplifier (1). 1. A nonlinear distortion compensation circuit for a high-output amplifier, characterized in that it is configured with a combining circuit (7) that outputs to the side.