JPH0629752A - Nonlinear compensating circuit and high frequency amplifier - Google Patents

Abstract

PURPOSE:To provide the nonlinear compensating circuit, which compensates not only the input/output characteristic but also the tertiary cross-modulation distortion for a low input signal, and the high frequency amplifier before which this nonlinear compensating circuit is placed. CONSTITUTION:A branching device 1 branches an input signal S1 from an input terminal 101 into signals S2 and S3 with a level difference. Distortion generating circuits 117 and 18 have the same circuit constitution, and the circuit 17 improves the saturation area input/output characteristic of the high frequency amplifier which is placed after an output terminal 102 and is connected to it, and the circuit 18 improves the tertiary cross-modulation distortion at the time of low signal input. The output of the circuit 18 has the phase and the amplitude adjusted by a phase device 15 and an attenuator 16 and becomes a signal opposite to the tertiary cross-modulation distortion for low signal input of the high frequency amplifier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear compensation circuit for compensating the non-linearity of input / output characteristics and third-order cross-modulation distortion generated by a high-frequency amplifier such as a traveling wave tube amplifier, the non-linear compensation circuit and the non-linear compensation circuit. It relates to a high-frequency amplifier including a traveling-wave amplifier connected in a back-end.

[0002]

2. Description of the Related Art A conventional non-linear compensation circuit of this type will be described with reference to the block diagram of FIG. 2. In this non-linear compensation circuit, most of a high frequency input signal S21 input from an input terminal 21 is converted into a signal S22. , A branching device 22 for branching the remaining part of the input signal S21 into a signal S23, and a signal S
The distortion generating amplifier 23 for amplifying the signal 22, the main amplifier 24 for amplifying the signal S23 having almost the same characteristics as the distortion generating amplifier 23, and the part of the amplified signal S22 and the signal S23 are almost the same. And a combiner 25 which produces an output signal S24 at the output terminal 26 by combining in the opposite phase.

In the above non-linear compensation circuit, the distortion generating amplifier 23 and the main amplifier 24 are constructed by using transistor amplifying elements of the same standard, and have substantially the same transmission characteristics such as amplitude characteristics, delay characteristics, gain and input / output characteristics. It is said that.
However, the distortion generating amplifier 23 does not operate at the high level signal S22.
Is input to operate in the non-linear range,
Transmission distortion occurs. On the other hand, the main amplifier 24 operates in the linear range and does not generate transmission distortion. These amplifiers 2
When the signals S22 and S23 amplified by 3 and 24 are combined under the condition that the phases of the signals S23 are almost opposite to each other and the amplitude of the signal S23 is large, an input / output characteristic opposite to that of a general high frequency amplifier is generated.
That is, in this non-linear compensation circuit, the increase rate of the output signal S24 is larger than the increase rate of the input signal S21. Therefore, if this non-linear compensation circuit is placed in front of a compensated high frequency amplifier (not shown) connected to the output terminal 26, a high frequency amplifier in which the total input / output characteristics are linearly compensated is obtained. Such a high-frequency amplifier is disclosed in, for example, Japanese Patent Publication (JP-B-58-16).
802).

[0004]

The prior art non-linear compensation circuit described above includes some types of traveling wave tube amplifiers (eg,
When the output backoff is compensated for in the region of output backoff 1 to 5 dB in combination with the stepped Helix TWT, the output backoff 5
There is a drawback that the third-order cross-modulation distortion is deteriorated in the region of dB or more as compared with the case of only the traveling wave tube amplifier. This is because the phase of the third-order intermodulation distortion generated in the above-mentioned non-linear compensation circuit does not change significantly even if the input level of the signal changes.
This is because the phase of the third-order cross-modulation distortion generated from the traveling-wave tube amplifier largely changes depending on the value of the input level, so that the third-order cross-modulation distortion of the traveling-wave tube amplifier can be canceled only in a part of the input level region.

[0005]

A nonlinear compensating circuit according to the present invention comprises a first branching device for branching a high-frequency input signal into a low-level first signal and a second-level signal higher than the first signal; Even if the high-frequency amplifier included in the first passage operates in a non-linear range, the first passage and the second passage have the high-frequency amplifier and have a substantially equal electric characteristic, and the high-frequency amplifier is provided in the second passage. Second branching means for branching the first signal in different level relationships and coupling it to the input of the first parallel path, so that the included high-frequency amplifier can operate in a linear range; and each of the pair of first parallel paths. The output of the second passage is larger than the output of the first passage, and the first combining means for performing vector combination in the opposite phase, and the third and fourth passages have high-frequency amplifiers and are substantially equal. A pair of first having electrical characteristics Parallel passage and said third said even the high-frequency amplifiers included in the passage is operated in the nonlinear range 4
Third branching means for branching the second signal with different level relationships and coupling it to the input of the second parallel path so that the high frequency amplifier included in the path can operate in a linear range; and a pair of the second parallel paths. Second synthesizing means for making the respective outputs of the above-mentioned outputs substantially equal to each other and performing vector synthesizing in the opposite phase, phase / amplitude adjusting means for adjusting the output of the second synthesizer to a predetermined output phase and output amplitude, and the first A third combiner for combining the combiner output and the phase / amplitude adjusting means output is provided.

Further, the high frequency amplifier of the present invention comprises:
A high-frequency amplifier having the described nonlinear compensation circuit and a traveling-wave tube amplifier that is post-connected to the nonlinear compensation circuit, including the first parallel path, the second branching means, and the first combining means. A first distortion generating circuit generates a signal for canceling a third-order intermodulation distortion component generated by the traveling wave tube amplifier in the output backoff region of 1 to 5 dB;
A second distortion generating circuit including the first parallel path, the second branching means, and the first combining means generates a third-order intermodulation distortion component generated in the region where the traveling wave tube amplifier has an output backoff of 5 dB or more. Generate a signal to cancel.

As described above, the non-linear compensation circuit of the present invention uses two distortion generation circuits for the third-order intermodulation distortion in the vicinity of the saturation region and the linear operation region, which are generated in the high-frequency amplifier such as the traveling-wave tube amplifier that follows. , For example, a first distortion generating circuit for compensating the third-order cross modulation distortion generated in the output back-off region of 1 to 5 dB of the high-frequency amplifier and a third distortion compensating circuit for compensating the third-order cross modulation distortion generated in the output back-off region of 5 dB or more. It can be canceled by the 2 distortion generating circuit. Therefore, if the non-linear compensation circuit of the present invention is placed in front of the high frequency amplifier, this total high frequency amplifier can reduce the third order intermodulation distortion in a wide range of signal input levels.

[0008]

The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. The branching device 1 of this non-linear distortion compensation circuit has an input terminal 10
Most of the high frequency input signal S1 input from 1 is used as the signal S3 supplied to the branching device 9 in the distortion generator 18, and the remaining part is used as the signal S2 supplied to the branching device 2 in the distortion generator 17. Two
Branch off.

The distortion generating circuit 17 is a circuit for compensating for third-order intermodulation distortion in the output backoff range of 1 to 5 dB of a high frequency amplifier (not shown) such as a traveling wave amplifier connected to the output terminal 102. It operates with the same configuration and operating principle as the conventional non-linear compensation circuit shown in FIG. That is, the distortion generating circuit 17 is configured to detect the signal S2 input from the branching device 1.
Of the input signal S2 into a signal S5, a branching device 2 for branching the remaining part of the input signal S2 into a signal S5, a distortion generating amplifier 4 for amplifying the signal S4, and the above-mentioned distortion generating amplifier 4. A main amplifier 6 having characteristics and amplifying the signal S5, and a combiner 5 for combining the amplified signals S4 and S5 in substantially opposite phases to generate a signal (non-linear compensation signal) S8 are provided. . The distortion generator 17 further includes a phase shifter 3 in the front stage of the distortion generation amplifier 4 and an attenuator 7 in the rear stage of the main amplifier 6, so that the signal S4 and the signal S input to the combiner 5 can be obtained.
The phase and amplitude of No. 5 are optimized.

The distortion generating circuit 18 is a circuit for compensating for the third-order intermodulation distortion in the region of the output back-off of 5 dB or more of the high frequency amplifier, and has substantially the same configuration as the distortion generating circuit 17. That is, the distortion generating circuit 18 divides most of the signal S3 input from the splitter 1 into the signal S6 and splits the remaining part of the input signal S3 into the signal S7 and the signal S6.
, A main amplifier 13 that has substantially the same characteristics as the distortion generating amplifier 11 and amplifies the signal S7, the amplified signal S6 and the signal S7 are combined, and a signal ( Combiner 12 for producing a third order intermodulation signal) S9
And a phase shifter 3 arranged in front of the distortion generating amplifier 4,
And an attenuator 7 arranged after the main amplifier 6. However, since the distortion generating circuit 18 is supplied with the signal S3 having a level higher than the signal S2 supplied to the distortion generating circuit 17, the input signal S1 smaller than the distortion generating circuit 17 is supplied.
Distortion occurs at the level. Further, the phase shifter 10 and the attenuator 14 are set to make the phases of the amplified signals S6 and S7 substantially opposite to each other and to make both signal levels equal in amplitude when the input signal S1 has a predetermined level. Signal S6 and S7 are combined by the combiner 12
9 is only the third order intermodulation component of the high frequency amplifier.

The signal S8 from the distortion generating circuit 17 and the signal S9 generated from the distortion generating circuit 18 and passed through the phase shifter 15 and the attenuator 16 are combined by the combiner 8 and output terminal 10
2 output signal S10. The phase amount of the phase shifter 15 and the attenuation amount of the attenuator 16 are adjusted so that the output signal S9 of the attenuator 16 cancels out the third-order intermodulation component of 5 dB or more in output backoff generated by the high frequency amplifier. .

[0013]

As described above, the nonlinear compensating circuit of the present invention is provided with the first distortion generating circuit in order to improve the input / output characteristics of a high frequency amplifier such as a traveling wave tube amplifier, which is located near the saturation region. , A second distortion generating circuit for generating a signal for canceling the third-order intermodulation component of the high frequency amplifier at the time of a low input signal is provided, and as a result, the high frequency amplifier in front of the non-linear compensation circuit is close to the saturation region. Not only the input / output characteristics but also the third-order cross-modulation component at the time of a low input signal can be canceled out, so that the third-order cross-modulation distortion can be reduced in a wide signal input level range.

[Brief description of drawings]

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

FIG. 2 is a block diagram of a conventional nonlinear compensation circuit.

[Explanation of symbols]

 1,2,9 Brancher 3,10,15 Phaser 4,6,11,13 Amplifier 7,14,16 Attenuator 5,8,12 Combiner 17,18 Distortion generator 101 Input terminal 102 Output terminal 21 Input Terminal 22 Brancher 23, 24 Amplifier 25 Combiner 26 Output terminal

Claims (2)

[Claims] 1. A first branching device for branching a high frequency input signal into a low level first signal and a second signal having a higher level than the first signal, and a high frequency amplifier in each of the first and second paths. A pair of first parallel passages having substantially equal electrical characteristics,
The first signal is branched in different level relationships so that the high frequency amplifier included in the second path can operate in a linear range even if the high frequency amplifier included in the first path operates in a non-linear range. Second branching means coupled to the input of one parallel path, and outputs of each of the pair of first parallel paths such that the output of the second path is larger than the output of the first path and the vectors are combined in antiphase. A first synthesizing means, a pair of second parallel passages having third and fourth passages each having a high-frequency amplifier and substantially equal electrical characteristics, and the high-frequency amplifier included in the third passage operate in a non-linear range. Still, third branching means for branching the second signal in different level relations and coupling to the input of the second parallel path so that the high frequency amplifier included in the fourth path can operate in a linear range, Of the above Second synthesizing means for making the outputs of the two parallel paths substantially equal to each other and synthesizing the vectors in antiphase; and phase / amplitude adjusting means for adjusting the output of the second synthesizer to a predetermined output phase and output amplitude. A third combining the output of the first combiner and the output of the phase / amplitude adjusting means
A nonlinear compensation circuit comprising: a combiner. 2. A high-frequency amplifier comprising the nonlinear compensating circuit according to claim 1 and a traveling-wave tube amplifier cascade-connected after the nonlinear compensating circuit, wherein the first parallel path and the second branching means are provided. A first distortion generating circuit including: and a first synthesizing unit generates a signal for canceling a third-order intermodulation distortion component generated by the traveling wave tube amplifier in the output backoff range of 1 to 5 dB, A second distortion generating circuit including a parallel path, the second branching means, and the first combining means, the traveling-wave tube amplifier outputs backoff 5
A high-frequency amplifier characterized by generating a signal for canceling a third-order intermodulation distortion component generated in a region of dB or more.