JPH01276809A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To hold the linearity of the input output characteristic of an electric amplifier itself by passing through a non-linear circuit to a detecting signal supplied to a comparator. CONSTITUTION:A part of the output of a second distributor 5 is detected and supplied as the input of one side of a comparator 9. A part of the output of a first distributor 2 detected by a first detector 7 is, for example, introduced through a non-linear circuit 10 composed of an LCR and an active signal into the other side input of the comparator 9. Consequently, the output of the comparator 9 detects the difference between both above-mentioned comparing input levels, and a signal level equivalent to the difference is supplied to a gain control circuit 3 as a gain control signal. Thus, no adverse influence will be given to the input output characteristic of the amplifier 4, an amplification efficiency is good and the influence of the temperature change can be compensated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to improvements in automatic gain control circuits used in power amplification stages of television transmitters and the like.

(Prior Art) As an automatic gain control circuit used in a power amplification stage of a television transmitter, the one shown in FIG. 4 is known.

That is, the high frequency signal supplied from the input terminal (1) is the first
The power 4W III m circuit (3
). The output signal of this gain control circuit (3) is introduced into and amplified by an amplifier (4), and taken out from an output terminal (6) via a second divider (5).

A part of this second divider (5) output is sent to the second detector (8).
) and is supplied to a comparator (9) together with a part of the output of the first distributor (2) detected by the first detector (7).

Therefore, the output of the comparator (9) detects the difference between the output levels of both the transverse transducers, and supplies a signal level corresponding to the difference to the gain control circuit (3) as a gain control signal.

By the way, solid-state power amplifier circuits for video signal amplification of television transmitters amplify high frequency signals that have been amplitude modulated (8M)b by the video signal, so high efficiency and good linearity are required, and A8 class It's working.

The input/output operating characteristics of the amplifier (4) itself are shown by the thick line (A) in Figure 5.
), when the input level is from O to A1, the input/output characteristics are almost linear, and after that, the characteristics gradually become curved and reach the saturation region. In order to achieve high efficiency amplification, it is necessary to operate the amplifier so that the output level is between B1 and 132 in the output level range from the non-linear region to the saturation region. Now, in the automatic gain control circuit shown in FIG. 4, if the gain control condition is set to 81/A1 = constant, the operating characteristic curve of the automatic gain control circuit will be as shown by the thin line (B) in FIG. Up to level A2, a linear amplification characteristic is shown to satisfy the condition that Bl/A1=constant.

Therefore, the input of the AM wave whose input peak value is A1 shown in Figure 6 (a) is naturally in the linear amplification characteristic region, so the output is a faithful output as shown in Figure 6 (b). is (q).If the input peak value reaches the level of A2 as shown in Fig. 7(a), when an AM wave is introduced into this automatic gain control circuit, it will operate in a non-linear region. , the output signal is as shown in FIG. 2(b), the degree of modulation changes greatly, and there is a drawback that an output faithful to the input AM wave cannot be obtained.

If the automatic gain control circuit is not used and only the amplifier (4) is operated, the input and output signal waveforms will have a slight peak as shown in input (a) and output (b) in Figure 8. Although some portions are compressed, a fairly high fidelity output signal is obtained.

The main purpose of automatic gain 1q control circuits for power amplifiers is to compensate for amplifier gain fluctuations due to temperature changes, but conventionally it has been difficult to realize a circuit that simultaneously satisfies this and the linearity of input/output characteristics. It was difficult.

(Problems to be Solved by the Invention) When a conventional automatic primary power control device is operated at an efficient operating point, it has a negative effect on input/output characteristics.

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic gain control circuit that maintains the linearity of the input/output characteristics of the power amplifier itself and can perform efficient amplification.

[Structure of the Invention] (Means for Solving the Problems) The automatic gain control circuit of the present invention includes a first divider to which a high frequency signal is supplied, and a gain control circuit to which the signal from the first divider is supplied. a control circuit, an amplifier circuit into which a signal from the gain control circuit is introduced and the high frequency signal is amplified, a second distributor to which this amplifier circuit is connected, and a signal from the second distributor and A pair of detectors each detecting a signal from the first detector, and a detection signal is introduced into at least one of the outputs of the pair of detectors via a nonlinear circuit, and the outputs of the comparators are compared. The present invention is characterized by comprising a comparator that supplies the gain control circuit as a control signal.

(Function) Since the circuit of this invention passes a nonlinear circuit to at least one of the outputs of both transverse transducers, this nonlinear circuit characteristic allows the comparator output, which has been compensated for the nonlinear characteristic region of the amplifier circuit, to be used as a gain. By supplying it to a control circuit, it is possible to obtain an automatic gain control circuit with arbitrary input/output characteristics.

(Embodiments) Hereinafter, embodiments of the automatic gain control circuit of the present invention will be described with reference to the drawings.

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

That is, the high frequency signal supplied from the input terminal (1) is the first
The signal is supplied to the gain control circuit (3) via the divider (2). The output signal of this gain control circuit (3) is transmitted to the main amplifier (
4) and is amplified, and taken out from the output terminal (6) via the second distributor (5).

A part of this second divider (5) output is sent to the second detector (8).
) and is supplied as one input of the comparator (9). A part of the output of the first distributor (2) detected by the first detector (7) is connected to the other input of the comparator (9) through a non-linear circuit including, for example, an LCR and an active element. It is introduced via (10).

Therefore, the output of the comparator (9) detects the difference between the comparison input levels, and supplies a signal level corresponding to the difference to the gain control circuit (3) as a gain 1q control signal.

Now, if the input/output characteristic diagram of the nonlinear circuit (10) is shown as (G) in FIG. 2, the input/output characteristics of the automatic gain control circuit shown in FIG. 1 are as shown in FIG. 5. (A
> can be approximated to the input/output characteristics of the amplifier (4) alone. Therefore, in this case, the output waveform is less affected by the input level, and it is possible to obtain automatic gain control circuit characteristics that compensate for gain changes due to temperature with good amplification efficiency.

Next, another embodiment of the inventive circuit will be described with reference to FIG. In FIG. 3, the same components as in FIG. 1 are given the same reference numerals, and detailed explanations are omitted. It is connected between the circuit (8) and the comparator (9).

Therefore, in this case, by configuring the nonlinear characteristics of the LCR, active elements, etc. as shown in (11) in Figure 2, distortion of the opposite characteristic is similarly applied in advance, and as shown in Figure 3. The input/output characteristics of the automatic column 1q control circuit can be approximated to the input/output characteristics of the amplifier (4) alone as shown in FIG. Therefore, in this case as well, the output waveform is less influenced by the input level, and it is possible to obtain automatic gain control circuit characteristics that compensate for gain changes due to temperature.

[Effects of the Invention] As described above, the automatic gain control circuit of the present invention has no adverse effect on the input/output characteristics of the amplifier as a result of passing at least one of the detected signals supplied to the comparator through the nonlinear circuit. , has good amplification efficiency, and can compensate for the effects of temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the automatic gain control circuit according to the present invention, FIG. 2 is an input/output signal waveform diagram showing the operating characteristics of the nonlinear circuit of the circuit shown in FIG. 4 is a block diagram showing another embodiment of the inventive circuit, FIG. 4 is a block diagram showing a conventional automatic gain control circuit, FIG. 5 is an input/output characteristic diagram of the amplifier and automatic gain control circuit, and FIGS. 6 and 7. 4 is an operating characteristic diagram of the circuit shown in FIG. 4, and FIG. 8 is a signal waveform diagram based on the input/output characteristics of the amplifier and the circuit shown in FIG. (2) (5)... 1st. Second divider (3)...gain control circuit (4)...amplifier (7) (8)...first... Second detector (9)...
Comparator (10)...Non-linear circuit agent Patent attorney Dian Hu Guo 1 Figure 2 Figure @ 3 Country Figure 6 W & 7 Figure 8

Claims (1)

[Claims] a first divider to which a high frequency signal is supplied; a gain control circuit to which a signal from the first divider is supplied; and an amplifier circuit into which the signal from the gain control circuit is introduced and amplifies the high frequency signal. a second divider to which this amplifier circuit is connected; a pair of detectors that respectively detect the signal from the second divider and the signal from the first detector; and the pair of detectors. An automatic gain control circuit comprising: a comparator that introduces and compares detected signals to at least one of the outputs via a nonlinear circuit, and supplies the comparator output as a control signal to the gain control circuit.