JPH0691398B2 - Automatic power control circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic control circuit corresponding to transmission power control of a transmitter used in a satellite communication earth station or the like.

[Prior Art] Conventionally, an automatic power control circuit of this type has a configuration shown in FIG. That is, in the conventional circuit shown in FIG. 3, the amplified input signal is passed through the voltage-controlled attenuator 4, a part of the output is detected by the detector 7, and the detected output is linearized and peak-held to obtain an error. The amplifier 10 detects an error voltage from the reference voltage and feeds it back to the voltage control attenuator 4 to control the output power.

[Problems to be Solved] In the above-described conventional automatic power control circuit, the detected voltage is different depending on the output waveform, and therefore, there is a drawback in that the output power is different due to the difference in carrier / modulation wave, one wave / a plurality of waves, or the like.

4 (a), (b), and (c) appear at points d, e, and f in FIG. 3 when a CW wave, a low bit rate phase-modulated wave, and a high bit rate phase-modulated wave are input, respectively. It shows a waveform. From this figure, peak hold output (point f)
In, it is understood that a large error occurs between each waveform.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide an automatic power control circuit capable of suppressing an error in output power even if an input waveform changes.

[Means for Solving the Problems] In order to achieve the above object, the present invention relates to a circuit that amplifies an input signal and outputs the amplified signal through a voltage-controlled attenuator and a detector, and an averaging circuit that averages the output voltage waveform of the detector. , Inputting the output voltage that passed through the averaging circuit and the rms value circuit, which has a time constant that is fast during charging and slow during discharging, and input a voltage corresponding to the error from the reference voltage to the voltage control attenuator An error amplifier for feedback is provided, and the voltage controlled attenuator is configured to change the attenuation amount of the input signal based on the voltage from the error amplifier.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an automatic power control circuit according to this embodiment. In the drawing, 1 and 2 are I for amplifying the input signal.
F amplifier and 3 are RF band power amplifiers. Further, 4 is a voltage controlled attenuator composed of a pin diode, 5 is an upconversion mixer, 6 is a local oscillator, and 7 is a wave detector for detecting a part of the output.

The input signal is amplified in the IF band, then frequency-converted to the RF band by the local oscillator 6 and the mixer 5, amplified by the power amplifier 3 and output. The detector 7 detects a part of this output, and detects the detected voltage by the following averaging circuit 8 and effective value circuit 9
Send to.

The averaging circuit 8 is composed of a low-pass filter having a sufficiently fast time constant and averages the detected voltage. RMS circuit 9
Is composed of a diode 9a, a resistor 9b, and a capacitor 9c, and has a time constant that is fast during charging and slow during discharging. That is,
The effective value circuit 9 performs an intermediate operation between the peak hold circuit and the averaging circuit.

2 (a), (b), and (c) are CW wave, low bit rate phase modulated wave (PSK wave), and high bit rate phase modulated wave, respectively. , shows the waveform that appears at point c.

As can be seen from FIG. 2, when a low bit rate PSK wave is input, the waveform is hardly changed in the averaging circuit 8 and is amplified, but in the effective value circuit 9, the charge / discharge time constant is different. Therefore, it changes between the average value (DC component) and the peak. The time constant of charging and discharging is almost DC
It should be decided to be equal to the value at CW.

When a PSK wave having a high bit rate is input, the waveform is blunted after passing through the averaging circuit 8 and oscillates around the average value of the waveform. Since the effective value circuit 9 can be regarded as a peak hold circuit at this time, it has a waveform at point c in FIG. 2 (c), and the error from CW is very small.

As described above, the effective value circuit 9 appropriately changes the charging / discharging time constant to reduce the difference between modulation / non-modulation when a low bit rate modulated wave is input. Then, the averaging circuit 8 passes the waveform as it is when the modulated wave has a low bit rate, and averages when the modulated bit has a high bit rate. By averaging the waveforms with these two circuits, the output speed can be changed / unmodulated over a wide range of transmission speeds, even if the input waveform changes, without changing the response speed of automatic voltage control. The error of electric power can be made very small.

The detection voltage averaged through the averaging circuit 8 and the effective value circuit 9 is input to the error amplifier 10. Error amplifier 10
Compares the input voltage with a reference voltage and feeds back a voltage corresponding to the error to the voltage controlled attenuator 4 to control the power.

The above-described automatic power control circuit according to the present embodiment keeps the output power substantially constant without being affected by the input waveform, and therefore has a small margin for the maximum output of the RF high power amplifier, and is inexpensive. . Further, it has a feature that highly precise control can be performed even when performing ALC operation of one wave / plural waves in multi-carrier operation or ALC operation in a modulated wave having a wide transmission rate.

[Effects of the Invention] As described above, the automatic power control circuit of the present invention has an effect of suppressing an error in output power even if the input waveform changes.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 (a), (b), and (c) are waveform diagrams of respective parts when a modulated / unmodulated wave is input, and FIG. FIG. 4A, FIG. 4B, and FIG. 4C are block diagrams of the circuit, and are waveform diagrams of respective parts when modulation / non-modulation is input to the conventional circuit. 1,2: IF amplifier, 3: RF power amplifier 4: Voltage control attenuator, 5: Mixer 6: Local oscillator, 7: Detector 8: Averaging circuit, 9: RMS circuit 10: Error amplifier

Claims (1)

[Claims] 1. A circuit for amplifying an input signal and outputting it through a voltage-controlled attenuator and a wave detector, and an averaging circuit for averaging the output voltage waveform of the wave detector and a time constant that is fast during charging and slow during discharging. And an error amplifier for inputting the output voltage that has passed through the averaging circuit and the rms circuit and feeding back a voltage corresponding to an error from the reference voltage to the voltage control attenuator. The attenuator is an automatic power control circuit characterized by changing the amount of attenuation of an input signal based on the voltage from the error amplifier.