JPH03177103A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To make the gain of a first amplifier large, and to make the difference of a signal level for every field small by smoothing a detected signal into a DC component. CONSTITUTION:The signal of an optional level inputted from an input terminal 1 is outputted through a gain variable circuit 2, and this signal is detected by a detecting circuit 4. The detected signal is turned into the DC component by a smoothion circuit 6, and is amplified by the first amplifier 5, and is transmitted to the sample hold circuit 7 of a following stage for each field. A control signal 9 held by each field is fed back for each field to the gain variable circuit 2, and the gain is controlled automatically for each field. After detecting the signal, smoothing the signal into the DC component by the smoothing circuit 6 before passing through the amplifier in such a way, the dynamic range of the first amplifier 5 can be expanded, and besides, the difference of the output level between the fields can be made smaller.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to electronic devices such as television receivers and video tape recorders (hereinafter abbreviated as VTR), regardless of the amplitude level of input signals. First, it relates to an automatic gain control device that outputs an amplitude at a constant level.

[Conventional technology]

A conventional automatic gain control device will be explained based on FIG.

In Fig. 2, ■ is an input terminal, 2 is a variable gain circuit, and 3 is a variable gain circuit.
1 is an output terminal, 4 is a detection circuit, 5 is a first amplifier, 7 is a sample hold circuit, 8 is a second amplifier, and 14 is a capacitor external to the IC.

The operation will be explained below.

The input signal at the input terminal 1 is amplified to a constant level by the variable gain circuit 2, and its output is detected by the detection circuit 4 and amplified by the first amplifier 5.

The amplified signal is smoothed by an external capacitor 14 and an internal resistor in a specific field, and the smoothed DC base part in other fields is held by a sample and hold circuit 7.

This smoothed signal 13 is amplified by the second amplifier 8,
The gain is adjusted with respect to the input signal level, and a signal at a constant level is output from the output terminal 3.

As shown in Fig. 3, the loop gain of the above automatic control system becomes (D) = + (C) - + (B
) → (A), the output becomes constant over a wide range of input signal levels.

Therefore, the loop gain is increased by increasing the gain of the first amplifier and further adding the second amplifier.

[Problem to be solved by the invention]

When trying to control the gain for each field (head) in a VTR, variations in the elements that make up the sample-and-hold circuit and variations in the external capacitors added to this are amplified by the second amplifier. The disparity in output level increases. Therefore, it is necessary to increase the gain of the first amplifier and decrease the gain of the second amplifier. However, the gain of the first amplifier is limited by the dynamic range of the sample and hold circuit in the next stage, and there is a problem that the gain of the first amplifier cannot be increased.

[Means to solve the problem]

In order to solve this problem, the present invention amplifies an input signal with a variable gain circuit, detects the amplified signal with a detection circuit, controls the gain of the variable gain circuit with the detected signal, and levels the input signal level. In an automatic gain control device configured to output an output signal of a constant signal level regardless of the magnitude of the signal, a detection signal smoothing circuit smoothes the signal detected by the detection circuit;
It is equipped with a first amplifier that amplifies the DC signal component of the signal smoothed by this detection signal smoothing circuit, and a sample hold circuit that holds the signal amplified by this first amplifier for each field, and the output of this sample hold circuit. The gain of the variable gain circuit is controlled by a signal.

[Function] In the present invention, since the signal is smoothed after being detected by the detection circuit, the detected signal becomes a DC signal component,
2/π, the dynamic range of the first amplifier is at least π/2 wider, and it is possible to increase the gain of the first amplifier and decrease the gain of the second amplifier, increasing the gain of the entire loop. At the same time, it is possible to realize gain control that keeps the output level constant over a wide range of input signal levels.

Also, since only one capacitor is needed externally for the IC, I
In addition to being suitable for C conversion, the gain of the second amplifier can be reduced, and the level difference between fields due to variations in external capacitors and IC internal elements can be reduced.

〔Example〕

Below, the automatic gain control device according to the present invention will be explained in detail based on the drawings.

Fig. 1 is a block diagram of an embodiment of an automatic gain control device of the present invention, Fig. 2 is a block diagram of an example of a conventional automatic gain control device, and Fig. 3 is an output amplitude with respect to manual amplitude due to differences in system gain. FIG.

In the drawing, 1 is an input terminal of this automatic gain control device, 2 is a variable gain circuit, 3 is an output terminal, 4 is a detection circuit, 5 is a first amplifier, 6
1 is a smoothing circuit, 7 is a sample and hold circuit, 8 is a second amplifier, 10 is an external capacitor, 11 is an IC built-in capacitor, and 9 is a control signal.

The operation of the automatic gain control device configured as above will be explained below.

A signal of an arbitrary level inputted from the input terminal l is outputted through the variable gain circuit 2. This output signal is detected by a detection circuit 4. The detected signal is sent to the smoothing circuit 6
becomes a DC component, is amplified by the first amplifier 5, and is transmitted to the next stage sample-and-hold circuit 7 for each field. The control signal 9 held for each field is fed back to the variable gain circuit 2 for each field,
Automatically adjusts the gain for each field.

According to the configuration of the embodiment of the present invention as described above, after the signal is detected, it is smoothed by the smoothing circuit before being passed through the amplifier to obtain a DC component, so that the dynamic range of the first amplifier is increased by at least π/2. As shown in Figure 3, as the gain increases, (D) → (C)
→(B)=+(A), it is possible to widen the range in which the output signal level is kept constant against changes in the input signal.

Furthermore, when the loop gain is constant, by increasing the gain of the second amplifier, the gain of the second amplifier can be made small or "l", thereby reducing the difference in output level between fields. becomes possible.

〔Effect of the invention〕

As described above, since the present invention smoothes the detected signal and converts it into a DC component, it is possible to increase the gain of the first amplifier and reduce the disparity in signal level for each field. An automatic gain control device with characteristics close to characteristic (A) can be realized.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of an automatic gain control device of the present invention, Fig. 2 is a block diagram of an example of a conventional automatic gain control device, and Fig. 3 is an output amplitude with respect to manual amplitude due to differences in system gain. FIG. l...Input terminal, 2...Variable gain circuit, 3...Output terminal, 4...Detection circuit, 5...First amplifier, 6...
...Smoothing circuit, 7...Sample and hold circuit, 8...
・Second amplifier, 9...Control signal, 10...External capacitor, 11...IC built-in capacitor 16-

Claims (1)

[Claims] The input signal is amplified by a variable gain circuit, the amplified signal is detected by a detection circuit, the gain of the variable gain circuit is controlled by the detected signal, and a constant signal level is output regardless of the magnitude of the input signal level. The automatic gain control device configured to output a signal includes a detection signal smoothing circuit for smoothing the signal detected by the detection circuit, and a detection signal smoothing circuit for amplifying the DC signal component of the signal smoothed by the detection signal smoothing circuit. 1 amplifier and a sample-and-hold circuit that holds the signal amplified by the first amplifier for each field, and the gain of the variable gain circuit is controlled by the output signal of this sample-and-hold circuit. automatic gain control device.