JPH03181286A - automatic gain control circuit - Google Patents

Abstract

PURPOSE:To use a similar circuit in common and to save number of circuit components by using a gain control voltage of a luminance signal processing circuit or a color signal processing circuit so as to control other gain simultaneously. CONSTITUTION:A luminance signal inputted from a luminance signal input terminal 1 is amplified to a proper level by a variable gain amplifier 2, one is fed to a synchronizing separator circuit 3 and synthesized at a mix circuit 4 with its output signal. The synthesized signal is held for a prescribed period at a sample-and-hold circuit 6 and one is fed back to the variable gain amplifier 2 as an automatic gain control voltage to keep the level outputted from a luminance signal output terminal 8 constant and the other is fed to other variable gain amplifier 10. Thus, a color signal inputted from a color signal input terminal is kept to a constant level by the variable gain amplifier and outputted from a color signal output terminal 17.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to, for example, a video tape recorder (hereinafter referred to as VT).
This relates to the automatic gain control voltage of the AGC (or ACC) circuit for automatically keeping the signal level of the signal (abbreviated as R) constant.

Conventional technology Conventionally, the automatic gain control circuit in a VTR has a configuration in which the luminance signal processing system and the chrominance signal processing system each have a similar automatic gain control circuit, as shown in Figures 3 and 4. there were. FIG. 3 shows an example of an AGC circuit for processing brightness signals of a VTR. In FIG. 3, 1 is a luminance signal input terminal;
2 is a variable gain amplifier, 3 is a synchronous separation circuit, 4 is a mix circuit, 5 is a detection circuit, 6 is a sample and hold circuit, 7 is an automatic gain control voltage, and 8 is a luminance signal output terminal. A luminance signal inputted from a luminance signal input terminal 1 is amplified to an appropriate level by a variable gain amplifier 2, one of which is supplied to a synchronization signal separation circuit 3, and combined with the output signal thereof by a mix circuit 4. This combined signal is detected by a detection circuit 5 and converted into a DC signal component. The converted signal is held in the sample-and-hold circuit 6 for a certain period of time, and is fed back to the variable gain amplifier 2 as an automatic gain control voltage 7, so that the output level of the luminance signal output terminal 8 is controlled to be constant. Further, FIG. 4 shows an example of an ACC circuit in color signal processing of a VTR. In Figure 4, 9
is a color signal input terminal, 10 is a variable gain amplifier, 11 is a burst gate circuit, 12 is a detection circuit, 13 is a comparator, 18
14 is a differential voltage, 14 is a reference voltage, 15 is a sample and hold circuit, 16 is an automatic gain control voltage, and 17 is a color signal output terminal. The color signal input from the color signal input terminal 9 is amplified to an appropriate level by a variable gain amplifier 10, and is supplied to a burst gate 11, where the burst signal portion is extracted. The extracted burst signal is detected by a detection circuit 12 and converted into a DC signal component. The converted DC signal component is compared with a reference voltage 14 by a comparator 13, and a difference voltage 1
8 is held in the sample and hold circuit 15 for a certain period of time, and is fed back to the variable gain amplifier 10 as an automatic gain control voltage, and is controlled so that the output level of the color signal output terminal 17 is constant.

Problems to be Solved by the Invention In such a conventional configuration, two sets of the same circuit (similar circuit) are required for the luminance signal processing system and the color signal processing system, resulting in a large and complicated circuit scale.

Means for Solving the Problems The present invention solves the above-mentioned conventional problems, and uses the automatic gain control voltage of either the luminance signal processing side or the chrominance signal processing side to simultaneously adjust the gain of the other variable gain amplifier. It consists of controlling.

Function With this configuration, conventionally the same circuit (similar circuit) was required on both the luminance signal processing side and the chrominance signal processing side in order to keep the output level constant, but it can be used for either side, and the circuit The number of elements can be significantly reduced.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a block diagram of an automatic gain control circuit in one embodiment of the present invention. In Figure 1, 1 is a luminance signal input terminal, 2 is a variable gain amplifier, 3 is a synchronous separation circuit, 4 is a mix circuit, 5 is a detection circuit, 6 is a sample and hold circuit, 10 is a variable gain amplifier, and 8 is a luminance signal Output terminal, 7 is automatic gain control voltage, 9 is color signal input terminal, 1
7 indicates a color signal output terminal.

The operation of the automatic gain control circuit of this embodiment configured as described above will be described below.

A luminance signal input from a luminance signal input terminal 1 is amplified to an appropriate level by a variable gain amplifier 2, one of which is supplied to a sync separation circuit 3, and mixed with the output signal thereof by a mix circuit 4. This synthesized signal is held in a sample-and-hold circuit 6 for a certain period of time, and as an automatic gain control voltage, one is fed back to the variable gain amplifier 2, the level output from the luminance signal output terminal 8 is kept constant, and the other is fed back to the variable gain amplifier 2. One is supplied to another variable gain amplifier 10.

As a result, the color signal input from the color signal input terminal is maintained at a constant level by the variable gain amplifier and output from the color signal output terminal 17.

As described above, according to this embodiment, by controlling the variable gain amplifier on the chrominance signal processing side using the automatic gain control voltage on the luminance signal processing side, the number of circuit elements can be reduced with a simple configuration.

FIG. 2 is a block diagram showing another embodiment of the invention. The difference from FIG. 1 is that the automatic gain control voltage is not directly supplied to the variable gain amplifier 10, but is compared with the reference voltage 14 of the color signal in the comparator 13, and the difference voltage 1
9 controls the gain of the variable gain amplifier 10. Further, by changing the reference voltage, an arbitrary output level can be set.

Effects of the Invention The present invention makes it possible to realize an excellent automatic gain control circuit that can reduce the number of circuit elements with a simple configuration by using a common automatic gain control voltage for the luminance signal processing system and the color signal processing system. be.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic gain control circuit according to an embodiment of the present invention, the second diagram is a block diagram showing another embodiment of the present invention, and FIG. 3 is a conventional automatic gain control circuit of a luminance signal processing system. FIG. 4 is a block diagram of a conventional automatic gain control circuit for a color signal processing system. 1... Brightness signal input terminal, 2... Variable gain amplifier, 3... Synchronization signal separation circuit, 4...
...Mix circuit, 5...Detection circuit, 6.
...Sample hold circuit, 7...Automatic gain control voltage, 8...Brightness signal output terminal, 9.
... Color signal input terminal, 10 ... Variable gain amplifier, 11 ... Burst gate circuit, 12.
...Detection circuit, 13...Comparator, 14.
...Reference voltage, 15...Sample and hold circuit, 16...Automatic gain control voltage, 17...
...Color signal output terminal, 18°19...Difference voltage.

Claims (2)

[Claims] (1) AGC automatic gain control (AGC
) circuit is provided with an automatic color signal level control (ACC) circuit as a color signal processing side circuit, and the gain control voltage of either the luminance signal processing side circuit or the color signal processing side circuit simultaneously controls the gain of the other. An automatic gain control circuit characterized in that: (2) Automatic gain control characterized in that the gain control voltage of one of the luminance signal processing circuit or the color signal processing circuit is compared with a reference voltage in a comparator, and the difference voltage is supplied to the other circuit as a gain control voltage. circuit.