# US 5,347,319 A · Circuit for regulating the color subcarrier amplitude in a video recorder

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- Number: US 5,347,319 A
- Document ID: US5347319A
- Status: Granted
- Kind: A
- Application number: 08/004,046
- Filed: 1993-01-15
- Granted: 1994-09-13
- Earliest claimed: 1992-01-22
- Assignees: Deutsche Thomson-Brandt GmbH
- Inventors: Helmut Sowig
- Web page: https://patentgrep.com/patent/US5347319A

## CPC

- H04N 9/793: for controlling the level of the chrominance signal, e.g. by means of automatic chroma control circuits
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

A circuit for regulating the color subcarrier amplitude in a video recorder used with a television receiver which employs overscanning of the electron beams for different modes of operation includes a regulating circuit for providing a regulating voltage representative of the amplitude of the color subcarrier. The regulating circuit includes a variable time constant circuit for switching from a short time constant during the overscanning to a long time constant immediately prior to ending the overscanning to change the regulating voltage in response to changes in the time constant. A variable amplifier is responsive to the regulating voltage to regulate the amplification of the color subcarrier in response to changes in the time constant.

## Claims

### Claim 1

A circuit for regulating the amplitude of a color subcarrier in a video recorder used with a television receiver which employs overscanning of electron beams, said circuit comprising:
means for receiving said color subcarrier and providing a regulating voltage representative of the amplitude of said color subcarrier, wherein said means for receiving includes variable time constant means for switching from a short time constant during an overscanning period of a television signal to a long time constant immediately prior to the end of said overscanning period so as to change said regulating voltage; and
a variable amplifier responsive to said regulating voltage for regulating the amplitude of said color subcarrier in response to said time constant changes.

### Claim 2 (depends on 1)

The circuit of claim 1 wherein said variable time constant means includes gate means for actuating said means for receiving during the presence of a color sync signal of said television receiver.

### Claim 3 (depends on 2)

The circuit of claim 2 wherein said variable time constant means includes a RC network having parallel capacitors and a voltage responsive switch for switching one of said capacitors into and out of said variable time constant means.

### Claim 4 (depends on 3)

The circuit of claim 3 wherein said voltage responsive switch is a transistor.

### Claim 5 (depends on 2)

The circuit of claim 2 wherein said means for receiving includes a constant current source and a variable resistance for changing the output current of said constant current source.

### Claim 6 (depends on 5)

The circuit of claim 5 wherein said variable resistance includes parallel resistors and a voltage responsive switch for switching one of said resistors into and out of said means for receiving.

### Claim 7 (depends on 6)

The circuit of claim 6 wherein said voltage responsive switch is a transistor.

### Claim 8

A method of regulating the amplitude of a color subcarrier in a video recorder for recording and playing various forms of television signals by using overscanning of the visible portion of a television signal comprising the steps of:
providing a first regulating voltage to adjust the amplitude of said color subcarrier to a value permitting rapid changes to said amplitude in response to head changes in said recorder by switching a regulation circuit to a first time constant during said overscanning; and
providing a second regulating voltage to adjust the amplitude of said color subcarrier to a value which avoids flicker in the first visible line scanned in said visible portion by switching said regulation circuit to a second time constant, longer than said first time constant, before the first line of said visible portion of the television signal is scanned.