JPH05183359A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To suppress the phase fluctuation caused in the gain control in the automatic gain control circuit. CONSTITUTION:The circuit provided with a variable gain amplifier 1, an amplitude detector 3, a low pass filter 4, a DC amplifier 5 and a reference voltage source 6 or the like and controlling a gain of the variable gain amplifier 1 to control automatically the gain is provided with a variable phase shifter 2 used to compensate the phase rotation of an output signal from the variable gain amplifier 1, an A/D converter 7 A/D-converting the gain control voltage to control the gain of the variable gain amplifier 1 and a storage means 8 reading data written in advance therein in response to an output of the A/D converter 7 and controlling a phase shift of the variable phase shifter 2 based on the data. The phase shift of the output signal of the variable gain amplifier 1 whose phase is fluctuated in response to the gain control voltage is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control circuit for a receiver which utilizes phase information of a received signal, and more particularly to an automatic gain control circuit which prevents phase fluctuation.

[0002]

2. Description of the Related Art A conventional automatic gain control circuit performs automatic gain control by inserting a variable gain amplifier into a receiving system and controlling the gain of the variable gain amplifier according to the strength of a received input signal. There is.

[0003]

However, in the conventional automatic gain control circuit of this type, the phase characteristic in the circuit is apt to change, and the automatic gain control circuit of the automatic gain control circuit changes due to the change of the gain control voltage depending on the strength of the input signal. It was difficult to keep the phase difference at the input end, that is, the phase rotation amount constant. Therefore, a receiver that causes a problem of absolute phase difference fluctuation in the automatic gain control circuit, for example, a tracking receiver that detects an angular error signal for automatic tracking of an antenna, or an accurate carrier phase from an earth station to a satellite In a Phase Transfer Link system receiver that transmits the signal, there is a problem in that it is impossible to detect and transmit with high precision due to the fluctuation of the absolute phase difference.
An object of the present invention is to provide an automatic gain control circuit in which no phase fluctuation occurs.

[0004]

According to the present invention, a circuit for controlling the gain of a variable gain amplifier according to a received signal level to automatically control the gain is provided for compensating for phase rotation of an output signal of the variable gain amplifier. Variable phase shifter and A / D for A / D converting gain control voltage for controlling gain of variable gain amplifier
The converter includes a converter and a storage unit that reads out data written in advance according to the output of the A / D converter and controls the phase shift amount of the variable phase shifter based on the data.

[0005]

According to the present invention, the amount of phase shift corresponding to the gain control voltage is read from the storage means, and the amount of phase shift of the signal output from the variable gain amplifier is controlled based on the read data, thereby changing the phase shift. To eliminate.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, reference numeral 1 is a variable gain amplifier whose gain is variably controlled according to the input signal level of the receiver, and 2 is a variable shift amplifier that compensates for phase fluctuations that occur when the variable gain amplifier 1 changes its gain. Phaser 3 is an amplitude detector that detects the output signal level output from the variable gain amplifier 1, and 4 is a low-pass filter that removes high-frequency components contained in the output voltage of the amplitude detector 3. is there. Further, 5 is a DC voltage detected by the amplitude detector 3 and the low-pass filter 4, and a reference voltage source 6
Is a direct current amplifier for comparing the voltage E _S of the DC voltage and amplifying the difference voltage. I am configuring.

Further, an A / D converter 7 for A / D converting the output of the DC amplifier 5, and a ROM (read only memory) in which phase rotation amounts are set for different addresses, respectively.
8 is connected, and the variable phase shifter 2 is controlled by the output of the ROM 8.

In such a negative feedback loop, by setting the DC gain of the DC amplifier 5 sufficiently large,
The gain control of the variable gain amplifier 1 is automatically performed so that the input voltage of the DC amplifier 5 becomes equal to the voltage E _S of the reference voltage generation source 6. As a result, the output signal levels of the variable gain amplifier 1 and the variable phase shifter 2, which are the output signals of the automatic gain control circuit, are subjected to automatic gain control to a constant output signal level determined by the reference voltage E _S.

The gain control voltage, which is the output voltage of the DC amplifier 5, is A / D converted in the A / D converter 7,
The data after D conversion is supplied to the address port of the ROM 8. The ROM 8 outputs data necessary for controlling the variable phase shifter 2 from the A / D converted gain control voltage which is input data, and supplies the data to the variable phase shifter 2 to control the amount of phase shift.

As shown in FIG. 2, the ROM 8 is pre-written with a conversion table for performing conversion satisfying the relationship between the gain control voltage and the phase rotation amount of the variable phase shifter. That is, FIG. 2 shows the amount of phase rotation with respect to the gain control voltage of the variable gain amplifier 1 as 9, and the amount of phase rotation with respect to the gain control voltage of the variable phase shifter for compensating for the variation of this phase rotation as 10. Therefore, the phase rotation amount 10 is read from the ROM 8, the phase shift amount of the variable phase shifter 2 is controlled based on the read data, and the phase shift amount is added to the phase of the variable gain amplifier 1 to output the output signal. Can be constant regardless of the gain control voltage.

[0011]

As described above, according to the present invention, the phase shift amount of the output is controlled based on the phase shift amount read according to the gain control voltage for performing the automatic gain control. Can compensate for phase variations,
There is an effect that it is possible to configure an automatic gain control circuit in which the phase is not changed even by the gain control.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an automatic gain control circuit of the present invention.

FIG. 2 is a diagram showing a correlation between an input signal level and a phase rotation amount (phase difference).

[Explanation of symbols]

 1 Variable Gain Amplifier 2 Variable Phase Shifter 3 Amplitude Detector 4 Low-pass Filter 5 DC Amplifier 6 Reference Voltage Source 7 A / D Converter 8 ROM

Claims (1)

[Claims] 1. A variable gain amplifier for amplifying a received signal, an amplitude detector for detecting an output amplitude of the variable gain amplifier, a low-pass filter for extracting only a DC voltage from the output amplitude, and an extracted signal. A DC amplifier that obtains a voltage difference between a DC voltage and a reference voltage and outputs a gain control voltage of the variable gain amplifier, a variable phase shifter for compensating a phase rotation of an output signal of the variable gain amplifier, and the DC An A / D converter for A / D converting the output voltage of the amplifier, and data written in advance based on the output of the A / D converter, and the shift of the variable phase shifter based on the read data. An automatic gain control circuit comprising: a storage unit for controlling a phase amount.