JP3112912B2 - Power control circuit of high frequency amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to, for example, a power control circuit of a high-frequency amplifier for controlling output power of a microwave band amplifier.

(Prior art) Some high-frequency amplifiers monitor the output power to detect the error power, and provide negative feedback to the input side to control the input level, thereby keeping the output level constant. Some have. FIG. 3 shows a power control circuit of a conventional high-frequency amplifier.

In FIG. 3, a high-frequency signal input to an input terminal 1 is amplified by a high-frequency amplifier circuit 3 via a variable attenuator 2 and output from an output terminal 4. Part of the output of the high-frequency amplifier circuit 3 is sent to a detection circuit 6, where it is converted into a DC voltage. This DC voltage is sent to the differential amplifying circuit 5 together with the reference voltage obtained by the reference voltage generating circuit 7, becomes an error voltage, and is negatively fed back to the variable attenuator 2. The variable attenuator 2 increases or decreases the input level in accordance with the error voltage, and matches the DC voltage with the reference voltage. Thus, the output level, that is, the input level is controlled according to the increase or decrease of the output power, and the output power can be stabilized.

However, in the power control circuit of the conventional high-frequency amplifier, the power control function operates even when there is no signal, and the high-frequency amplifier 3 is controlled so that the set reference voltage value and the detection voltage become equal.
The attenuation of the variable attenuator 2 inserted into the input of the variable a. Therefore, for example, when a pulse-like burst signal as shown in FIG. 4 (a) is inputted, the amount of attenuation of the variable attenuator 2 becomes as shown in FIG. Cannot catch up, and the input of the high-frequency amplifier 3 becomes an excessive input as shown in FIG. 4 (c), so that the output is saturated as shown in FIG. 4 (d). Therefore,
Harmonics and third-order intermodulation distortion appear in the output, and AM-PM
There is a disadvantage that a non-linear phenomenon such as deterioration of the conversion coefficient occurs. Further, even if the signal is a continuous wave, the input becomes similarly excessive at the time of startup, and the high-frequency amplifier 3 is saturated.

(Problems to be Solved by the Invention) As described above, in the power control circuit of the conventional high-frequency amplifier, the power control function cannot catch up at the time of start-up or signal rise, and the high-frequency amplifier circuit is saturated to cause a nonlinear phenomenon.

The present invention has been made to eliminate the above disadvantages,
An object of the present invention is to provide a power control circuit of a high-frequency amplifier capable of preventing saturation of a high-frequency amplifier circuit at the time of signal rise or start-up and suppressing a nonlinear phenomenon.

[Means for Solving the Problems] To achieve the above object, the present invention provides a variable attenuator for level-limiting a high-frequency signal supplied to a high-frequency amplifier according to a control signal, and a variable attenuator for the high-frequency amplifier. A detection circuit that extracts a part of the output and performs DC detection, and a differential amplifier circuit that detects an error voltage by taking a difference between the DC voltage detected by the detection circuit and a first reference voltage; In a power control circuit of a high-frequency amplifier for stabilizing the output power of the high-frequency amplifier by negatively feeding back the variable attenuator as a control signal to control the amount of attenuation, the path of the negative feedback is turned on / off. A switch to be controlled, and a second switch whose DC voltage detected by the detection circuit is lower than the first reference voltage.
A level comparator that sets the switch to an on state when the voltage is equal to or higher than a reference voltage, and sets the switch to an off state when the voltage is less than a second reference voltage. Control signal generating means for adding the error voltage and a third reference voltage via a time constant circuit in a path, wherein the control signal generating means controls the third reference voltage when the switch is off. Is supplied to the variable attenuator as a control signal, and in the ON state of the switch, the error voltage and the third reference voltage are added via the time constant circuit, and this is added to the variable attenuator as a control signal. The time constant circuit changes the control signal during the on / off control of the switch transiently.

(Operation) In the power control circuit of the high-frequency amplifier having the above configuration, when the high-frequency signal input is in a no-signal state, and the DC voltage is detected by the detection circuit, if the DC voltage is less than the second reference voltage, the switch is turned off. And the third reference voltage is supplied to the variable attenuator as a control signal, so that the attenuation is maintained at a specified value. In this state, when a high-frequency signal is input and the DC voltage detected by the detection circuit becomes equal to or higher than the second reference voltage, the switch is set to the ON state, and the error voltage obtained by the differential amplifier circuit is changed to the third reference voltage. Is added to
Since this is supplied to the variable attenuator as a control signal, the attenuation is increased or decreased from a specified value in accordance with a change in the error voltage. At this time, since the error voltage and the third reference voltage are added through the time constant circuit, the control signal when the switch is turned on changes transiently. As a result, even if a high-frequency signal enters from a no-signal state, it is possible to prevent the saturation of the input of the high-frequency amplifier and suppress the nonlinear phenomenon. Further, even when the switch is off, the control signal changes transiently by the time constant circuit, so that even if the input signal is a pulse signal, the amount of attenuation between pulses is controlled to be substantially constant.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG. 1 and FIG. However, in FIG. 1, the same portions as those in FIG. 3 are denoted by the same reference numerals, and different portions will be mainly described here.

Figure 1 is shows the configuration, a DC voltage V _D obtained by the detection circuit 6 is the reference voltage generating circuit (hereinafter, a first
_Is supplied to the differential amplifier circuit (hereinafter, referred to as a first differential amplifier circuit) 5 together with the first reference voltage V _R1 generated by the reference voltage generation circuit 7, where the error voltage V _E is supplied. Is detected. Further, the DC voltage V _D is supplied to the level comparator 9 with the second reference voltage V _R2 generated by the second reference voltage generating circuit 8. The second reference voltage V _R2 is for ON / OFF determination of the power control function.

The level comparator 9 compares the levels of the input voltages V _D and V _R2 , and when V _D <V _R2 , turns on / off the power control function switch 15.
Is turned off, and the switch 15 is turned on when V _D > V _R2 . Error voltage V _E obtained in the first differential amplifier circuit 5 is supplied to the second differential amplifier circuit 14 via the switch 15, the resistor 11.

The third reference voltage V _R3 generated by the third reference voltage generation circuit 10 is also supplied to the second differential amplifier circuit 14 via the resistor 12. The third reference voltage V _R3 is for setting an initial attenuation amount. A resistor 13 is connected in parallel with a capacitor 13
A predetermined time constant is set together with 11. Also the capacitor
13 performs the oscillation preventing function together with the resistor 11. The second differential amplifier circuit 14 and outputs an input voltage by impedance conversion, the output voltage V _C is supplied to the control input of the variable attenuator 2 as a negative feedback control voltage.

The operation of the above configuration will be described below with reference to FIG.

Now, it is assumed that the pulse signal shown in FIG. 2A is supplied to the input terminal 1 from the no-signal state at time t. When there is no signal, the output voltage V _D of the detection circuit 6 is 0 V, so that V _D <V
_R2 , and the switch 15 is off as shown in FIG. 2 (b). Therefore, the second differential amplifier circuit 14
Only the third reference voltage V _R3 is supplied to this voltage V _R3 is supplied to the variable attenuator 2 as an initial control voltage V _C. Therefore, the variable attenuator 2 has a constant value in the initial state, as shown in FIG. 2 (c). This initial attenuation,
That is, the value of the third reference voltage V _R3 is set to be larger than the amount of attenuation in the steady state where the switch 15 is turned on.

Pulse signal in this state is input, becomes high level, as shown in FIG. 2 (a), since the detected DC voltage V _D exceeds the second reference voltage V _R2, in FIG. 2 (b) As shown, the switch 15 is turned on, and the first differential amplifier circuit 5
In the detected error voltage V _E is added to the third reference voltage V _R3. At this time, since the input voltage of the second differential amplifier circuit 14 changes with the time constant of the resistors 11, 12 and the capacitor 13, the variable attenuator transiently decreases as shown in FIG. I do. Therefore, the input of the high-frequency amplifier circuit 3 does not saturate at the rising edge as shown in FIG. 2D, and as shown in FIG. It does not appear or the AM-PM conversion coefficient deteriorates.

Further, when the pulse signal becomes a low level (= 0V) as shown in FIG. 2 (a), since the detected DC voltage V _D is equal to or less than the second reference voltage V _R2, Fig. 2 (b) the switch 15 as shown in turned off, the detected error voltage V _E is blocked by the first differential amplifier circuit 5. However, since this period is extremely short, the input voltage of the second differential amplifier circuit 14
The voltage value at the moment when the switch 15 is turned off from on is hardly changed by the time constants of the capacitors 11 and 12 and the capacitor 13. Accordingly, the amount of attenuation becomes constant as shown in FIG. 2 (c), and the input / output waveform of the high frequency amplifier circuit 3 falls as shown in FIGS. 2 (d) and 2 (e). At the next rise, the input of the variable attenuator does not saturate because the variable attenuator has almost the optimum value.

Further, if there is no signal, the detected DC voltage V _D
Becomes lower than or equal to the second reference voltage V _R2 , the switch 15 is turned off, and the error voltage _VE is cut off. Then, the input voltage of the second differential amplifier circuit 14 gradually decreases due to the time constant of the resistors 11 and 12 and the capacitor 13, and finally the third reference voltage
V _R3 only. Therefore, the attenuation of the variable attenuator 2 is returned to the initial attenuation.

Therefore, since the power control circuit having the above configuration gives a certain amount of initial attenuation when there is no signal, it is possible to prevent saturation of the high-frequency amplifier circuit at the time of inputting a pulse signal and suppress a nonlinear phenomenon.

In the above embodiment, the case of inputting a pulse signal has been described, but it goes without saying that a similar effect can be obtained even when the continuous wave signal is started.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a power control circuit of a high-frequency amplifier capable of preventing saturation of a high-frequency amplifier circuit at the time of signal rise or start-up and suppressing a nonlinear phenomenon. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a power control circuit of a high-frequency amplifier according to the present invention, FIG. 2 is a waveform diagram for explaining the operation of the embodiment, and FIG. FIG. 4 is a block diagram showing the configuration of the power control circuit, and FIG. 4 is a waveform diagram for explaining the operation of the conventional circuit. DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Variable attenuator, 3 ... High frequency amplifier circuit, 4 ... Output terminal, 5 ... Differential amplifier circuit, 6 ... Detector circuit, 7 ... First reference voltage generation circuit , V _D ... DC detection voltage, V _R1 ... first reference voltage, V _E ... error voltage, 8
... A second reference voltage generating circuit, V _R2 ... A second reference voltage, 9... A level comparator, 10... A third reference voltage generating circuit, V _R3 . 12 ... resistor, 13 ... capacitor, 14 ... second differential amplifier circuit, 15 ... switch, V _C ... negative feedback control voltage.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03G 3/20-3/34

Claims (2)

(57) [Claims] 1. A variable attenuator for level-limiting a high-frequency signal supplied to a high-frequency amplifier in accordance with a control signal, a detection circuit for extracting a part of the output of the high-frequency amplifier and performing DC detection, A differential amplifying circuit that detects an error voltage by taking a difference between the DC voltage and the first reference voltage, and controls the amount of attenuation by negatively feeding back the variable attenuator using the error voltage as a control signal. Thus, in the power control circuit of the high-frequency amplifier for stabilizing the output power of the high-frequency amplifier, a switch for controlling on / off of the path of the negative feedback, and a DC voltage detected by the detection circuit is the first reference. The switch is turned on when the voltage is equal to or higher than a second reference voltage lower than the voltage, and when the voltage is lower than the second reference voltage, the switch is turned on. A level comparator for setting a switch to an off state; and a control signal generating means for adding the error voltage and a third reference voltage via a time constant circuit in a path from the switch of the negative feedback to the variable attenuator. The control signal generating means supplies the third reference voltage as a control signal to the variable attenuator when the switch is off, and supplies the error voltage and the third voltage when the switch is on. A reference voltage is added to the variable attenuator as a control signal through the time constant circuit, and a change in the control signal during on / off control of the switch is determined by the time constant circuit. A power control circuit for a high-frequency amplifier, which is changed transiently. 2. The control signal generating means generates the third reference voltage such that an amount of attenuation of the variable attenuator when the switch is off is greater than an amount of attenuation when the switch is on. Claim (1)
A power control circuit for the high-frequency amplifier according to claim 1.