JPS5828924B2 - automatic gain control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic gain control device for AM-modulated carrier signals and the like.

In automatic gain control methods for AM-modulated carrier signals, waveform distortion of the modulated wave signal may pose a problem.

For example, in television relay broadcasting equipment O, synchronization type (sag) may occur depending on the time constant of the automatic gain control system, so a capacitor is inserted to increase the time constant to prevent this from occurring.

However, if the time constant is increased, it will take time for the control to respond, resulting in excessive output when input radio waves rush in, resulting in an increase in power of 1.
You can destroy Shirobe.

For this reason, conventionally, as shown in Fig. 1, in order to control the gain of the gain control amplifier 11, the wave is detected by a detector 12, 13, and then an internal automatic gain control circuit (internal AGC) 14 with a fast response and an external circuit with a large time constant are used. Automatic gain control circuit (external AGC) 1
5 and two automatic gain control systems are provided, and the internal AGC setting value 14 is set higher than the external AGC setting value 15,
Normal control is performed by the external AGC 15, and the internal AGC 14 is operated to protect the power amplification section 16 when the input suddenly increases, such as at the start of broadcasting.

However, even in this case, as shown in FIG.
When the power amplifiers 161, 162, . It increases and reaches the set value G of the internal AGC 14.

Then, gain control is performed by the internal AGC 14, causing a sag, which becomes a problem.

The present invention eliminates these drawbacks, and examples thereof will be explained below.

In FIG. 3, the same parts as those constituting the apparatus in FIG. 1 are given the same reference numerals.

The difference is that each quick response circuit 17 is included in the automatic gain control system 17.
a and the slow response circuit 17b are provided in parallel, and each quick response circuit 17a
is set higher than the setting value of the slow response circuit 17b, and each quick response circuit 17a is used to increase the power amplification section 1 when the input suddenly increases.
6 etc., and the slow response circuit 17b performs automatic gain control without sag during normal operation.

Therefore, responsiveness is good and waveform distortion does not occur (/agitation gain control can be performed).

Furthermore, FIGS. 4 and 5 each show an example in which a double detection type detector 18 is used for a multi-frequency signal such as a television signal (automatic gain control is set to 0), and each of the immediate response circuits 17a1 By providing the slow response circuit 17b, automatic gain control with excellent transient characteristics and sufficient protection against sudden increases in input can be performed with just one system.

Incidentally, FIG. 6 shows the specific configuration of each quick response circuit 17a1 and slow response circuit 17b in FIGS. 3 to 5 described above.
It is composed of diodes 19 and 20, amplifiers 21 and 22, a capacitor 23, and the like.

It goes without saying that, as shown in FIG. 6, the time constant elements of each immediate response circuit may be omitted and the time constants specific to the diodes and amplifier elements may be utilized.

As is clear from the above embodiments, according to the present invention, since the amplifier, the time constant circuit, and the detection diode are connected in series, it is possible to cope with excessive input without impairing the response characteristics. Since the output is commonly input to two response circuits with different response characteristics, the transient response characteristics are improved and an automatic gain control device with high reliability against level fluctuations is obtained. A gain control device having a gain control device can be provided.

[Brief explanation of the drawing]

1 and 2 are block diagrams of a conventional automatic gain control device, FIG. 3 is a block diagram of an automatic gain control device according to one embodiment of the present invention, and FIG. 4 is a block diagram of another embodiment. FIG. 5 is a block diagram of still another embodiment, and FIG. 6 is a wiring diagram of the main parts. 11...gain control amplifier, 12...detector, 17a...immediate response circuits, 17b...
...Slow response circuit.

Claims (1)

[Claims] 1. Each of the outputs of the same two-type detector is inputted, and each quick response circuit and slow response circuit have different response speeds, each consisting of an amplifier, a time constant circuit, and a detection diode connected in series,
A gain control circuit that controls the gain of the television signal according to the outputs of both the quick response circuits and the slow response circuit, and the amplifier, adjust the output settings of the quick response circuits from the output settings of the slow response circuit. An automatic gain control device characterized in that by setting the gain to a high value, the quick response circuits perform automatic gain in response to a sudden increase in input, and the slow response circuit performs automatic gain in normal times.