JPH03214914A - High frequency power control circuit - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the electric performance in a power amplifier and to improve the service life of the amplifier itself by adding a diode newly to a time constant circuit being a component of a control system. CONSTITUTION:When a steep high frequency signal rising as a pulse from a high frequency signal source 1 is fed to a variable attenuator 2, since a diode 83 is connected in the forward polarity to a resistor 81 of a time constant circuit 8, a steep and high control signal from a differential amplifier 6 conducts the diode 83 in the forward direction to control the variable attenuator 2 while promoting the charging of a parallel capacitor 82 having been so far discharged. Thus, the control system with a short over-saturation operating time is formed. Thus, production of a harmonic wave or intermodulation wave is suppressed and the deterioration in the performance such as AM-PM conversion coefficient and a high frequency amplifier 3 itself is prevented.

Description

[Detailed description of the invention]

[Object of the Invention] (Industrial Application Field) The present invention relates to improvements in high frequency power control circuits used, for example, in the microwave band. (Prior Art) In a microwave band high frequency power amplifier, the level of the amplified output signal is always kept almost constant by monitoring the amplified output signal and giving negative feedback to the monitored output signal. As such, a high frequency power control circuit is used to control the input power level to the amplifier. Figure Wja is a circuit diagram of a conventional high frequency power control circuit. That is, a high frequency signal from a microwave band high frequency signal source 1 is supplied to a power amplifier 3 via a variable attenuator 2. Power amplification! ! 3 amplifies the high frequency signal from the variable attenuator 2 and outputs it to the output terminal 4. A part of the output signal is detected by a detector 5 composed of a detection diode, etc., and the detected output voltage is a differential The signal is supplied to an amplifier 6. Differential amplifier 6
introduces the DC reference voltage from the reference voltage source 7 together with the DC detection output voltage from the detector 5, and derives an output signal corresponding to the voltage level difference between the two signals as a negative feedback control signal. The output signal of the differential amplifier 6 is supplied as a control signal to the variable attenuator 2 via a time constant circuit 8 consisting of a series resistor 8l and a parallel capacitor 82. In the high frequency power control circuit shown in FIG. 4, even if there is no high frequency signal introduced into the variable attenuator 2, that is, the power level of the input high frequency signal is close to zero, the negative feedback control system functions effectively. In order to obtain a predetermined output power, circuit conditions are set in advance so that the output of the differential amplifier 6 is zero when the amount of attenuation of the variable attenuator 2 is minimum. Therefore, under such circuit conditions, if a high frequency signal with a steep rise in the form of a pulse is applied to the variable attenuator 2, the control system will not be able to follow it immediately, and the output power waveform of the power amplifier 3 will change. This will result in large distortions. That is, when a pulsed high frequency signal as shown in FIG. 5(a) is supplied from the high frequency signal source l to the variable attenuator 2, the amount of attenuation of the variable attenuator 2 is as shown in FIG. 5(b). , the curve cannot be followed immediately at the rising edge of 11 and the falling edge of t1, and a gentle rising and falling curve is drawn. Therefore, the input high frequency signal at the high frequency amplifier 3 is as shown in FIG.
As shown in e), a transiently excessive input voltage is input as is at time ti. Therefore, since the high frequency amplifier 3 itself has saturation amplification characteristics, its output signal continues at the saturation voltage level V from 11 to t2 as shown in FIG. Reach (at t3)
It exhibits the characteristic of gradually decreasing up to . In other words, the operating characteristics shown in FIG. 5 depend on the attenuation characteristics of the variable attenuator 2 based on the response characteristics of the negative feedback control system, so if there is a sudden change in the input level, the output level of the power amplifier 3 will temporarily change. It fluctuates and deviates from its steady state value. When the variation (deviation amount) of the output level is ΔPo, the time constant τ of the time constant circuit 8 is uniquely determined by the resistance value of the series resistor 8l and the capacitance value of the parallel capacitor 82, and is shown in FIG. As shown, it always shows a constant value regardless of the value of ΔPo. Therefore, even if the high frequency power input to the variable attenuator 2 suddenly increases in a pulsed manner, the variable attenuator 2 depends on the response characteristics determined by the time constant circuit 8, so the operating characteristics of the power amplifier 3 are Figure 5 (c). (d) is inevitable. When the high frequency amplifier 3 operates under saturation characteristics, nonlinear phenomena occur, such as harmonics, third-order mutual distortion waves, etc.
It has the disadvantage of deteriorating the M-PM conversion coefficients. Furthermore, when the operating time (tl-t2) under the oversaturation characteristic becomes longer, a problem arises in that the amplifying elements such as transistors constituting the power amplifier 3 accelerate deterioration and shorten their lifespan. (Problem to be Solved by the Invention) In conventional high-frequency power control circuits, when the high-frequency power supplied to the variable attenuator suddenly increases, the response in the negative feedback system cannot respond immediately, so the power amplifier is overloaded. Improvements have been desired since this increases the load and causes nonlinear phenomena and deterioration of the amplifier. SUMMARY OF THE INVENTION An object of the present invention is to provide a high frequency power control circuit that can eliminate the above-mentioned conventional drawbacks, shorten the operating time at least in the saturation region, reduce nonlinear phenomena, and improve the life of the amplifier.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a variable attenuator that introduces a high frequency signal, a power amplifier connected to the variable attenuator, a detector that introduces a part of the output of the power amplifier, A differential amplifier which introduces the detection output signal of this detector and a reference voltage signal and derives an output corresponding to the difference signal, and which is connected to this differential amplifier and uses the output corresponding to the difference signal as a control signal. In a high frequency power control circuit comprising a time constant circuit consisting of a series resistor and a parallel capacitor connected to supply power to a variable attenuator, a diode is connected in parallel to the series resistor of the time constant circuit, and a diode is connected in parallel to the series resistor of the time constant circuit. The feature is that the circuit time constant is changed according to the diode conduction characteristics when the signal attenuation increases. (Function) In the high frequency power control circuit according to the present invention, a diode is connected in parallel to the series resistance of the time constant circuit, and when the amount of signal attenuation in the variable attenuator increases, the conduction characteristics of the diode change correspondingly. This enables instantaneous charging of parallel capacitors. Therefore, since the circuit time constant can be changed to a small value, a control signal with a sharp rise is supplied to the variable attenuator in immediate response to an increase in the amount of attenuation, and the amplification saturation time of the power amplifier can be shortened. (Embodiment) Hereinafter, one embodiment of the high frequency power control circuit according to the present invention will be described in detail with reference to the drawings. Components that are the same as those shown in FIG. 4 will be described with the same reference numerals. That is, a high frequency signal from a high frequency signal source 1 is supplied to a power amplifier 3 via a variable attenuator 2, power amplified, and output from an output terminal 4. A part of the output signal of the power amplifier 3 is detected by a wave detector 5 and supplied to a differential amplifier B together with a DC reference voltage from a reference voltage source 7. The output of the differential amplifier G is sent to the time constant circuit 8 as an attenuation control signal.
is supplied to The time constant circuit 8 is constructed by connecting a diode 83 in parallel to a series resistor 81, a parallel capacitor 82, and a series resistor 8l so as to be in the forward control direction. The output of the time constant circuit 8 is connected to be supplied to the variable attenuator 2 as an attenuation amount control signal, thereby forming a negative feedback circuit. Therefore, like the conventional variable attenuator 2, the control range of the amount of attenuation is set to be quite wide, so that a predetermined power amplification output can be obtained even when the power level of the input high frequency signal is close to zero. Circuit conditions are set in advance so that the output of the differential amplifier 6 is zero when the attenuation of the amplifier 2 is at its minimum. In the circuit shown in FIG. 1, similarly to FIG. 5(a), a high-frequency signal that rises steeply in a pulsed manner is applied to the variable attenuator 2 from a high-frequency signal source l as shown in FIG. 2(a). To explain the case, in the feedback control system that controls the variable attenuator 2, the response time cannot be made completely zero, so the attenuation cannot immediately follow the time tl, but the A diode 83 is connected in the forward direction, and a sudden and excessive control signal from the differential amplifier 6 causes the diode 83 to conduct in the forward direction, and the parallel capacitor 82, which had been discharged until then, becomes conductive in the forward direction.
The variable attenuator 2 is controlled while promoting charging. In a normal control state, the diode 83 is in a cut-off state, and the time constant τ of the time constant circuit 8 is determined by the resistance value of the series resistor 8l and the capacitance value of the parallel capacitor 82.
When a large voltage control signal (output voltage of the differential amplifier 8) is applied, the variation ΔPo in the output level becomes large, the diode 83 becomes conductive so as to bypass the series resistor 8l, and the time constant τ changes depending on the diode 83. It is almost determined by the forward resistance value of the parallel capacitor 82 and the capacitance value of the parallel capacitor 82. That is, since the forward resistance value of the diode 83 is extremely small compared to the resistance value of the series resistor 8l, the time constant τ at that time also becomes small, resulting in a characteristic curve as shown in FIG. 3 for changes in ΔPo. From this, in response to the input of a high frequency signal as shown in FIG. 2(a), the variable attenuator 2 will respond as shown in FIG. 2(b).
Since the attenuation characteristic has a relatively steep rise, the input signal level and output signal level in the high frequency amplifier 3 are determined by the saturation time (tl) as shown in FIGS. 2(C) and (d), respectively.
~t2') is significantly shortened. As described above, the high frequency power control circuit according to the present invention has the following features:
When the input high-frequency power suddenly increases, the output level of the power amplifier 3 also fluctuates as the signal power level fluctuates, but the time constant τ of the time constant circuit 8 changes in response to the increase in the fluctuation ΔPo. , it is possible to configure a control system with short oversaturation operation time. Therefore, according to the present invention, generation of harmonics, third-order mutual distortion waves, etc., which are drawbacks of the conventional method, can be suppressed, and there is an advantage that functional deterioration of the AM-PM conversion coefficient and the high frequency amplifier 3 itself can be prevented. [Effects of the Invention] The high-frequency power control circuit according to the present invention has a simple configuration in which a diode is newly added to the time constant circuit configured in the control system, thereby preventing electrical performance deterioration in the power amplifier and improving the efficiency of the amplifier itself. It improves the lifespan and exhibits remarkable effects when applied to high frequency amplification stages in microwave bands and the like.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the high frequency power control circuit according to the present invention, and FIGS. 2(a) to 2(d) are characteristic curve diagrams explaining the operating characteristics of the circuit shown in FIG. 1. , FIG. 3 is a time constant characteristic diagram of the high frequency power control circuit also shown in FIG. 1, FIG. 4 is a circuit configuration diagram showing a conventional high frequency power control circuit, and FIGS. 5(a) to 5(d) is a characteristic curve diagram explaining the operating characteristics of the circuit shown in FIG. 4, and FIG. 6 is a time constant characteristic diagram of the high frequency power control circuit also shown in FIG. 4. 1... High frequency signal source, 2... Variable attenuator, 3...
... Power amplifier circuit, 4... Output terminal, 5... Detector, 7... Reference voltage source, 8l... Series resistor, 82... Parallel capacitor, 83... Diode. 6... Differential amplifier, 8... Time constant circuit,

Claims (1)

[Claims] A variable attenuator that introduces a high frequency signal, a power amplifier connected to this variable attenuator, a detector that introduces a part of the output of this power amplifier, and a detected output signal of this detector and a reference voltage signal. a differential amplifier that derives an output corresponding to the difference signal, and a series resistor connected to the differential amplifier so as to supply the output corresponding to the difference signal as a control signal to the variable attenuator. In a high frequency power control circuit equipped with a time constant circuit consisting of a parallel capacitor, a diode is connected in parallel to the series resistor of the time constant circuit, and the diode conduction characteristics when the amount of signal attenuation in the variable attenuator increases A high-frequency power control circuit characterized by varying the circuit time constant.