JP2792436B2 - High frequency output amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency output amplifier, and more particularly to a microwave amplifier in which high efficiency and high linearity are required.

[0002]

2. Description of the Related Art In a conventional microwave amplifier, distortion is added to a stage preceding a final stage amplifier circuit which tends to cause non-linearity at an operating point where the efficiency is high, so as to cancel the distortion at the final stage. A pre-distortion method that improves the overall distortion or a negative feedback method that improves by negative feedback is used.

In the predistortion method, as shown in FIG. 3, an excitation amplifier circuit 23 which does not cause distortion due to low power.
Both the amplitude and phase distortion generated by the pre-distortion circuit inserted between the high-output amplifier circuit 23 and the last-stage high-power amplifier circuit 23, which is the source of distortion, cancels the distortion of the last stage 23.

In the negative feedback method, distortion is reduced by taking out a part of the output of the final stage and adding it to the input of the excitation stage with a phase that becomes negative feedback.

[0005]

In the conventional pre-distortion method, it is necessary to adjust the characteristics of the pre-distortion circuit in accordance with the distortion characteristics at the final stage. It took a lot of man-hours to make adjustments so that they could be canceled in response to changes in.

On the other hand, in the negative feedback method, since the change in the forward stage in the feedback loop is suppressed by the negative feedback, there is an advantage that the adjustment in individual devices is simplified. The phase shift in the circuit is large, and it is usually difficult to obtain a sufficient phase margin to prevent self-oscillation. This method is applicable only at a relatively low frequency of, for example, 1 to 2 GHz and a feedback amount of about several dB. .

[0007]

According to the present invention, the input R
The F signal is branched by a first branch circuit that branches into three, and one output signal of this branch circuit is detected by a first AM detection circuit to detect an envelope component of the RF signal. The other output of the first branch circuit is an AM modulator and a PM
The signal passes through the modulator, passes through the second branch circuit, and is amplified by the high-power amplifier circuit to obtain a predetermined output. A third three-branch circuit is further provided at the output end of the high-power amplifier circuit. One is an output RF signal, and the other is detected by a second AM detection circuit to detect an envelope component of the RF signal. You. The envelope component obtained from the third branch circuit is compared with the envelope component obtained from the first branch circuit by a comparison circuit, and the obtained difference signal is applied to an AM modulator,
The distortion in the high-power amplifier is corrected by modulating the F signal, that is, by constructing a negative feedback circuit and keeping the overall gain constant.

Further, when the input signal level of the high-output amplifier circuit exceeds the saturation input point, the above correction does not function properly. Therefore, the envelope component is detected by the detection circuit provided in the second branch circuit. , An ALC circuit having a saturation input point of the high-power amplifier circuit as a threshold point. That is, the envelope components are compared, and the resulting voltage is applied to an AM modulation circuit to form an ALC. An OR circuit is provided on the input side of the AM modulation circuit in order to switch the constant gain negative feedback circuit and the ALC circuit at the saturation input point of the high output amplifier circuit.

The remaining one of the first branch circuits and the third
The other output signal of the branch circuit is phase-detected by a phase comparator, and the output voltage is compared with a reference voltage by a comparator so that the phase difference between the input RF signal and the output RF signal is always constant. The output is applied to a PM modulator to form a negative feedback circuit.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 shows a microwave amplifier circuit with a nonlinear compensation circuit according to one embodiment of the present invention.

In the figure, RF input from an input terminal 1
The signal is branched by a branch circuit 2, and the branched signal is further branched into two, one of which is input by an AM detection circuit 8 into an input RF signal.
The envelope component of the signal is detected and input to the comparison circuit 9. At this time, the input RF signal is amplified by the high output amplifier circuit 6 through the AM modulation circuit 3, the PM modulation circuit 4, and the branch circuit 5. On the other hand, the output of the high-power amplifier circuit 6 is branched by the branch circuit 7, the main signal is branched to the output terminal 16, and the branched signal is further branched, while the amplitude component of the output RF signal is detected by the AM detector 13.

The output of the AM detector 13 is input to a comparison circuit 9 and compared with the amplitude component of the input RF signal to obtain a difference signal. The difference signal passes through the OR circuit 10 and the AM modulation circuit 3
Is applied to The AM modulation circuit 3 operates so as to constitute a negative feedback circuit so that the difference signal becomes small. Therefore, the AM modulation circuit 3 operates so as to compensate for the gain compression by the high-power amplifier circuit 6 and to make the gain from the input terminal 1 to the output terminal 16 constant.

However, when the input of the high-power amplifier 6 reaches the saturation input point, the output of the high-output amplifier 6 does not increase, no matter how much the output of the AM modulator 3 is increased. Further, there is a possibility that the high output amplifier circuit 6 may be damaged. Therefore, the branch circuit 5 is provided at the input end of the high-output amplifier circuit 6, the amplitude of the branched signal is detected by the AM detection circuit 2, and is compared with the reference voltage 15 by the comparison circuit 11.
Therefore, when the output voltage of the comparison circuit 11 exceeds the input saturation point of the high-output amplification circuit 6, the output voltage of the comparison circuit 11 sharply increases.
Is applied to the AM modulation circuit 3 to reduce the output signal power of the AM modulation circuit 3. That is, it operates as an ALC circuit that keeps the input signal level of the high output amplifier circuit 6 constant.

Next, the operation of the OR circuit 10 will be described. Generally, the input / output characteristics of the high-output amplifier circuit 6 are shown in FIG.
As shown in (1), the gain is reduced as the saturation point is approached. Therefore, the gain from the input terminal 1 to the input terminal of the high-power amplifier 6 gradually increases with the amplification of the input power, and the gain must increase rapidly near the saturation point. AM
Assuming that the higher the applied voltage of the modulation circuit is, the smaller the gain is, the output voltage of the comparison circuit 9 rapidly decreases near the saturation point. In addition, the output voltage of the comparison circuit 11 gradually increases when the input power gradually increases and reaches a saturation point.
It crosses with the output voltage of the comparison circuit 9 as shown in FIG.
Therefore, the OR circuit 10 determines which of the larger voltages is A
FIG. 2 shows a desired characteristic by applying the voltage to the M modulation circuit 3.
(C) is obtained. At this time, from input terminal 1 to output terminal 1
The input / output characteristics up to 6 are as shown in FIG.

Further, in the present invention, the other signal which has been branched by the branch circuit 2 and further branched into two is applied to the phase detection circuit 14 and branched by the branch circuit 7 to further branch.
The phase difference between the other one of the branched signals and the phase detection circuit 14 is detected. This detection result is negatively fed back to the PM modulation circuit 4 and controlled so that the phase difference between the input and output signals is always constant.

[0016]

As described above, the high-frequency output amplifier of the present invention has a characteristic that the gain is constant and the input / output characteristics are linear when the input is below the saturation point, and the output is constant when the input is above the saturation point. With. Further, since the input / output phase characteristics are controlled by the negative feedback circuit so as to be always constant, they have almost ideal cross-modulation characteristics.

According to the simulation, the third-order intermodulation characteristic of the circuit having such input / output characteristics is approximately 18 dB at C / 3IM at the saturation point, and 2 dB input
At the back-off point, C / 3IM becomes almost infinite at the 21 dB and 3 dB back-off points.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing characteristics of a high-output amplifier according to the present invention;
Is the input / output characteristic example of the amplifier circuit, (b) is the modulation input voltage of the AM modulation circuit, (c) is the gain up to the high-output amplifier circuit input,
(D) shows an example of improved combined input / output characteristics according to the present invention.

FIG. 3 is a diagram showing a conventional high-output amplifier having a pre-distortion type nonlinear compensation circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input terminal 2 Branch circuit 3 AM modulation circuit 4 PM modulation circuit 5 Branch circuit 6 High output amplification circuit 7 Branch circuit 8, 12, 13 AM detection circuit 9, 11, Comparison circuit 10 OR circuit 14 Phase detection circuit 15 Reference voltage 16 Output Terminal 20 Input terminal 21 Predistortion nonlinear compensation circuit 22 Excitation amplification circuit 23 High output amplification circuit 24 Output terminal

Claims (2)

(57) [Claims] A first branch circuit, an amplitude modulator, a phase modulator, a second branch circuit, a high-frequency high-power amplifier circuit, and a third branch circuit connected in cascade; A first amplitude detector for detecting an envelope amplitude of an input signal branched by a circuit, and a third amplitude detector for detecting an envelope amplitude of an output signal of the high-frequency high-power amplifier branched from a third branch circuit. An amplitude detector, and first and third
A constant-gain feedback unit comprising a first differential amplifier for amplifying the difference between the output signals of the amplitude detectors, and an envelope amplitude of the high-frequency high-output amplifier input signal branched by a second branch circuit. A second amplitude detector for detecting, and an output of the second amplitude detector for increasing the high-frequency high power.
Second comparison with the reference voltage corresponding to the saturation input point of the width circuit
A constant output feedback unit composed of a differential amplifier of any one of the following; and one of an output of a first differential amplifier of the constant gain feedback unit and an output of a second differential amplifier of the constant output feedback unit. An amplitude linear circuit having an OR circuit and applying an output of the OR circuit to the amplitude modulation circuit, wherein an input is saturated.
When the sum is below the sum, the gain is constant and the input exceeds the saturation point
A high-frequency output amplifier whose output is constant at times. 2. A phase detector for detecting a phase difference between an input signal branched by a first branch circuit and an output signal branched by a third branch circuit; and an output of the phase detector as a reference voltage. 2. The high-frequency output amplifier according to claim 1, comprising: a third differential amplifier to be compared; and a phase linearization circuit configured to apply an output of the third differential amplifier to the phase modulator.