JPH0653765A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To keep an output power from a 1st burst output to a prescribed output level in the sample-and-hold type automatic gain control circuit keeping a burst output to a prescribed output level. CONSTITUTION:The control circuit is provided with 1st and 2nd changeover devices 12, 13 used to make an output signal of a modulator 3 to be a nonmodulation signal and with a high speed 2nd sample-and-hold circuit 15 operated for a period when the nonmodulation signal is outputted, and a period for some bits for nonmodulation is provided before a burst output, and the high speed 2nd sample-and-hold circuit 15 is operated for this period to keep the output power constant to make the output power constant from the 1st burst output.

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, and more particularly to an automatic gain control circuit for controlling output power of burst output used in a time division multiple access communication system or the like.

[0002]

2. Description of the Related Art In a time division multiple access communication system in which it is necessary to send a transmission signal in a burst form, a continuous automatic gain control circuit can be used for controlling the output power of the transmission signal because the output signal is not continuous. Instead, a sample-and-hold type automatic gain control circuit that normally forms a loop only during a period when an output signal is output is used.

FIG. 3 is a block diagram of an example of a conventional automatic gain control circuit. The output modulation signal of the modulator 3, which is modulated by the data signal applied to the modulation signal input terminals 1 and 2, is amplified by the voltage control variable gain amplifier 5 via the switch 4 and output to the output terminal 6. The output power of the voltage controlled variable gain amplifier 5 is detected by the detector 7, and the detected voltage is band-limited by the low-pass filter 8 and then applied to the sample hold circuit 9. Further, the output voltage of the sample hold circuit 9 is subjected to voltage amplification of the difference from the reference voltage by the differential amplifier 10, and the gain of the voltage control variable gain amplifier 5 is controlled by this output voltage.

The controller 11 designates the timing of burst output, and the output waveform thereof, as shown in FIG. 4, when the output is "H", the switch 4 and the sample hold circuit 9 operate to form a loop. When the output is "L", the switch 4 and the sample hold circuit 9 are disconnected, the loop is opened, and the sample hold circuit 9 holds the detection voltage when the loop is formed, and the next burst. The initial output is kept constant when output is output.

[0005]

In this conventional automatic gain control circuit, since the detection voltage of the previous burst is held after the burst output is output several times, the output voltage can be kept constant. Although it is possible, it is difficult to keep the output power level of the first burst output after the power is applied or the burst output that is output after the hold time is exceeded at a constant level.

As an example of an improvement measure, a fixed voltage predicted to obtain an average output power level is stored, and the fixed voltage is used to output the output voltage at the first time or during a burst after the hold period has passed. Although a method of controlling the level is also used, there is no guarantee that the output power will be kept constant or within the specified range due to temperature fluctuations of the amplifier or the like, and this is not a complete measure.

[0007]

SUMMARY OF THE INVENTION An automatic gain control circuit according to the present invention comprises a modulator for modulating an input data signal and outputting it as a modulation signal, a switch for intermittently switching the modulation signal at a specific timing, and a switch for the switch. A voltage controlled variable gain amplifier for amplifying an output signal, a detector for detecting the output power of the voltage controlled variable gain amplifier, a first low-pass filter for averaging the output voltage of the detector, and A first sample-hold circuit for sampling and holding the voltage from the low-pass filter 1, a differential amplifier for taking out a difference between the first sample-held voltage and a reference voltage, and an output of the differential amplifier The gain of the voltage controlled variable gain amplifier is controlled by the voltage, and the automatic gain control circuit that makes the connection timing of the switch and the operation timing of the sample hold circuit coincide with each other. In the circuit, a circuit for applying a voltage that does not modulate the modulation signal from the modulator to the modulator, a wideband second low-pass filter for extracting the envelope voltage of the detector, and the second low-pass filter. A second sample-hold circuit for sampling and holding the output voltage of the filter, and operating the second sample-hold circuit only during a period when the modulation signal of the modulator is unmodulated. .

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a timing diagram showing the operation of the controller of this embodiment.

In this embodiment shown in FIG. 1, a modulator 3 which modulates an input data signal and outputs it as a modulation signal, and this modulator 3
Switch 4 that intermittently outputs the output signal of
A voltage control variable gain amplifier 5 for amplifying the output signal of the switch 4, a detector 7 for detecting the output power of the voltage control variable gain amplifier 5, and a first for averaging the output voltage of the detector 7. Low-pass filter 8 and first low-pass filter 8
First sample-hold circuit 9 that samples and holds the output voltage of the differential amplifier 10, a differential amplifier 10 that extracts the difference between the sampled and held voltage and the reference voltage, and a differential amplifier 10.
The output voltage of the voltage-controlled variable gain amplifier 5 is controlled by the output voltage, and the connection timing of the switch 4 and the operation timing of the first sample-hold circuit 9 are made to coincide with each other to modulate the voltage that does not modulate the output modulation signal. The first and second switching devices 12 and 13 added to the detector 3, and the second low-pass filter 1 in the high band for extracting the envelope voltage of the detector 7 as it is.
4, a second sample and hold circuit 15 for sampling and holding the output voltage of the second low pass filter 14, and a modulator 3
The second sample-and-hold circuit 15 is operated only during the period when the modulated signal of 1 is unmodulated.

Next, the operation of this embodiment will be described. The data applied to the data input terminals 1 and 2 is applied to the modulator 3 via the first and second switchers 12 and 13, and the modulation signal output from the modulator 3 modulated by this data is output to the switch 4 Is amplified by the voltage control variable gain amplifier 5 and output to the output terminal 6. Voltage controlled variable gain amplifier 5
The output power is detected by the detector 7, the detected voltage is band-limited by the first low-pass filter 8 having a narrow band, and then applied to the first sample-hold circuit 9. Further, the output voltage of the first sample-hold circuit 9 undergoes voltage amplification of the difference from the reference voltage by the differential amplifier 10, and the output power controls the gain of the voltage-controlled variable gain amplifier 5.

The output voltage of the detector 7 is applied to the second low-pass filter 14 in the high band, and after being band-limited, it is applied to the second sample-hold circuit 15. The output voltages of the first sample and hold circuit 9 and the second sample and hold circuit 15 are both applied to the differential amplifier 10, and the switching of the output voltage is performed by the controller 11 as shown in FIG.
When 1 is added, the burst signal 11 delayed by N clocks 11
2, the burst signal 113 delayed by N−n clocks is generated inside the controller 11, and the burst signal 113 is applied to the switch 4.

Next, timing signals 114 and 115 are generated, and the timing signal 114 is generated by the first and second switching devices 1.
2, 13 and the second sample and hold circuit 15, and the timing signal 115 is applied to the first sample and hold circuit 9. During the first n clock periods of the burst signal 113, the fixed voltage V1 and V2 are applied to the modulator 3 by the timing signal 114 in the first and second switching devices 12 and 13.
, And the output signal of the modulator 3 becomes a non-modulated signal. At the same time, the second sample hold circuit 15 is also operating, and the band of the low-pass filter 14 is wide, so that the loop operates at high speed and the output power is set immediately.

Next, during the period of the burst signal 112, the first and second switches 12 and 13 operate to apply data to the modulator 3, and the first sample and hold circuit 9 operates according to the timing signal 115. Therefore, the average value of the output power from the first low-pass filter 8 is detected and a slow sample-hold type loop operation is performed to maintain the output power level at a constant value.

With this configuration, even in the case of the modulation method in which the envelope of the output power varies, the output power is controlled from the first burst output by controlling the output power to be constant by the unmodulated signal of the first n clocks. Can be kept constant.

[0015]

As described above, according to the present invention, the output power can be kept constant from the first burst output by sending the unmodulated output of several clocks before the required burst output. Therefore, even in a modulation method in which the envelope of the modulated output signal changes, the first burst output is not affected by the response delay of the loop operation by the low-pass filter for averaging the envelope. Can be constant.

[Brief description of drawings]

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

FIG. 2 is a timing chart of the controller according to the present embodiment.

FIG. 3 is a block diagram of an example of a conventional automatic gain control circuit.

FIG. 4 is a timing chart for explaining an operation of a conventional example.

[Explanation of symbols]

 1, 2 data input terminal 3 modulator 4 switch 5 voltage control variable gain amplifier 6 output terminal 7 detector 8 first low-pass filter 9 first sample hold circuit 10 differential amplifier 11 controller 12 first Switcher 13 Second switcher 14 Second low-pass filter 15 Second sample and hold circuit 16 Timing signal input terminal 111 Timing signal 112 Burst signal 113 Burst signal 114 Timing signal 115 Timing signal

Claims (1)

[Claims] 1. A modulator for modulating an input data signal and outputting the modulated signal as a modulation signal, a switch for connecting and disconnecting the modulation signal at a specific timing, a voltage control variable gain amplifier for amplifying an output signal of the switch, and A detector that detects the output power of the voltage-controlled variable gain amplifier, a first low-pass filter that averages the output voltage of the detector, and a sample-hold voltage from the first low-pass filter. A first sample and hold circuit, a differential amplifier for extracting the difference between the first sampled and held voltage and a reference voltage, and the output voltage of the differential amplifier controls the gain of the voltage controlled variable gain amplifier. In addition, in the automatic gain control circuit that matches the connection timing of the switch and the operation timing of the sample hold circuit, the modulation signal from the modulator is not modulated. A circuit for applying a voltage to the modulator, a wideband second low-pass filter for extracting the envelope voltage of the detector, and a second sample-hold for the output voltage of the second low-pass filter. 2. The automatic gain control circuit according to claim 1, wherein the second sample and hold circuit is operated only during a period when the modulation signal of the modulator is unmodulated.