JP2919175B2 - Linear compensation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear compensation circuit for improving a linear distortion of a high-frequency circuit such as a cross-modulation distortion of a power amplifier, and more particularly to a linear compensation circuit for improving the linear distortion by an accurate control signal.

[0002]

2. Description of the Related Art FIG. 2 shows a block diagram of a linear compensating circuit for the purpose of amplitude compensation only.

In this linear compensation circuit, a high-frequency signal input from an input terminal 28 is branched into two by an input-side branch circuit 20. One of the high-frequency signals from the input-side branch circuit 20 is detected by the input detection circuit 26 as a forward DC voltage, and the other high-frequency signal is an amplitude compensation circuit responsive to a control signal from the bias line 24. 21 allows the level to be changed. The power amplifier 22 amplifies the high-frequency signal from the amplitude compensation circuit 21, and the high-frequency signal from the power amplifier 22 is branched into two by the output-side branch circuit 23. One of the high-frequency signals from the output side branch circuit 23 is output terminal 2
The other one of the high-frequency signals output from the output 9 is detected by the output detector 27 as a DC voltage in the opposite direction. The forward detection voltage is applied to a positive input terminal of the operational amplifier 25, and the negative detection voltage is applied to a negative input terminal of the operational amplifier 25. The operational amplifier 25 differentially amplifies the positive and negative voltages. As a result, the control signal is generated on the bias line 24.
This control signal controls the input power of the amplitude compensation circuit 21 and the output power of the power amplifier 22 to be equal.

[0004]

In the above-described linear compensation circuit of the prior art, a detection voltage signal corresponding to the input / output terminal power level is input to both the positive and negative input terminals of the operational amplifier, and the two signals are differentiated. The control signal was obtained by dynamic amplification. Then, a ratio (a common-mode signal rejection ratio) between the amplification degree for the in-phase input of the operational amplifier and the amplification degree for the differential input becomes a problem in obtaining an accurate control signal. Here, the differential gain is Av
d, if the common mode gain is Avc, then the common mode signal rejection ratio is | A
vd / Avc |. If this ratio is small, the operational amplifier cannot accurately amplify only the differential signal, and if the frequency of the control signal is high, this ratio is further reduced, resulting in a large linear compensation error.

[0005]

A linear compensation circuit according to the present invention comprises a first branch circuit for branching an input high-frequency signal into two, and converting one of the high-frequency signals from the first branch circuit into a first DC voltage. A first detection circuit, an amplitude compensation circuit for changing a level of another high-frequency signal from the first branch circuit in response to a control signal, and a high-frequency amplifier for amplifying the high-frequency signal from the amplitude compensation circuit. A second branch circuit that branches the high-frequency signal from the high-frequency amplifier into two, and a second branch circuit that converts one of the high-frequency signals from the second branch circuit into a second DC voltage having a polarity opposite to that of the first DC voltage. 2 detectors and 1st detector
Input terminal receives the first and second DC voltages and
And an operational amplifier for inputting a reference voltage and amplifying a difference between a sum voltage of the first and second DC voltages and the reference voltage to generate the control signal.

[0006]

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. This amplitude compensating circuit is intended only for amplitude compensation as in the conventional example of FIG.

In this linear compensation circuit, a high-frequency signal input from an input terminal 18 is branched into two by an input-side branch circuit 10. One of the high-frequency signals from the input-side branch circuit 10 is detected as a forward (positive) DC voltage by an input-side forward detection circuit 16 using a diode as a detection element, and the other high-frequency signal is biased. The level is changed by the amplitude compensation circuit 11 responsive to the control signal from the line 14. The power amplifier 12 amplifies the high-frequency signal from the amplitude compensation circuit 11, and the high-frequency signal from the power amplifier 12 is branched into two by an output-side branch circuit 13. One of the high-frequency signals from the output-side branch circuit 13 is output from an output terminal 19, and the other one of the high-frequency signals is subjected to a reverse (negative) direct current by an output-side reverse detector 17 using a diode as a detecting element. Detected by voltage.

The forward and negative detection voltages are applied to the same positive input terminal of an operational amplifier 15. The negative input terminal of the operational amplifier 15 is grounded to obtain a reference voltage. The operational amplifier 15 differentially amplifies the positive and negative detection voltages as a result, and generates the control signal on the bias line 24. This control signal controls the output level of the amplitude compensation circuit 11 so that the input power of the amplitude compensation circuit 11 and the output power of the power amplifier 12 become equal.

The operation of the amplitude compensation circuit shown in FIG. 1 will be described in more detail. The input powers of the input-side forward detection circuit 16 and the output-side reverse detection circuit 17 are at the same level when the power amplifier 12 operates sufficiently linearly. Thus, the coupling amount between the input-side branch circuit 10 and the output-side branch circuit 13 is adjusted.
As the input power versus output power characteristic of the power amplifier 12 becomes non-linear, the absolute value of the detection output of the input-side forward detection circuit 16 and the output-side reverse detection circuit 17 becomes different. Increase. Operational amplifier 15
Controls the amplitude compensation circuit 11 through the bias line 14 to change the amount of amplification or attenuation of the circuit 11. Therefore, the input power of the power amplifier 12 is controlled, and apparent linearity is maintained between the input terminal 18 and the output terminal 19.

In the above description, the input detection circuit 1
6 is a forward detection circuit, the output side detection circuit 17 is a reverse direction detection circuit, and the operational amplifier 15 is an in-phase amplifier, but the input side detection circuit 16 is a reverse direction detection circuit and the output side detection circuit 1.
The same effect can be obtained even if 7 is a forward detection circuit and the operational amplifier 15 is an inverting amplifier.

[0012]

As described above, the present invention detects two signals of input and output, and inputs the difference between the two signals to one input terminal of the operational amplifier. The polarities are reversed, and these detected DC voltages are input to the in-phase input terminal of an operational amplifier, and this operational amplifier is used as an in-phase amplifier. Therefore, when the operational amplifier is used as a differential amplifier, the effect of the common mode rejection ratio is eliminated, and the difference between the signal components between the input and output of the linear compensation circuit can be detected more accurately, and the detected signal is controlled by the linear compensator. There is an effect that a signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a linear compensation circuit according to the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 10, 20 Input side branch circuit 11, 21 Amplitude compensation circuit 12, 22 Power amplifier 13, 23 Output side branch circuit 14, 24 Bias line 15, 25 Operational amplifier 16 Input side forward branch circuit 17 Output side reverse branch circuit 18 , 28 input terminal 19, 29 output terminal 26 input detection circuit 27 output detection circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H03F 1/32 H03F 3/45

Claims (2)

(57) [Claims] 1. A first branch circuit for branching an input high-frequency signal into two, and one of the high-frequency signals from the first branch circuit is transmitted to a first branch circuit.
A first detection circuit for converting the high-frequency signal from the first branch circuit into a DC voltage, an amplitude compensation circuit for changing the level of another high-frequency signal from the first branch circuit in response to a control signal, and a high-frequency signal from the amplitude compensation circuit. A high-frequency amplifier for amplifying, a second branch circuit for branching the high-frequency signal from the high-frequency amplifier into two, and a second branch circuit having one of the high-frequency signals from the second branch circuit having a polarity opposite to that of the first DC voltage. A second detector for converting to a DC voltage, a first input terminal for inputting the first and second DC voltages, a second input terminal for inputting a reference voltage, and a sum of the first and second DC voltages; A linear compensation circuit comprising: an operational amplifier that amplifies a difference between a voltage and the reference voltage to generate the control signal. 2. The apparatus according to claim 1, wherein said first detection circuit is a diode detector that generates a positive DC voltage, and said second detection circuit is a diode detector that generates a negative DC voltage. A linear compensation circuit as described.