Patent US3622696A successfully refreshed from Google Patents.
US3622696A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Automatic contrast control for a television receiver
Assignee: Motorola Solutions Inc
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Filing: 1969-04-01
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Granted: 1971-11-23
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Expires: 1989-04-01
Abstract
Abstract A color television receiver using direct demodulation of the color and brightness signals supplies the output of the video amplifier stage through an automatic contrast control circuit including first and second light dependent resistors. The first light dependent resistor is subjected to the ambient light surrounding the receiver and operates in a voltage divider to provide a varying voltage in accordance with variations of the ambient light level. The output of the voltage divider is supplied through an integrating circuit to the base of a field effect transistor, the output of which is utilized to drive a lamp in an isolator package in which the second light dependent resistor is located. Variations of the light emanating from the lamp cause variations in the resistance of the second light dependent resistor, which is placed in series with the output of the video amplifier to variably attenuate the signals obtained therefrom to provide automatic contrast control. In addition, there is disclosed an automatic brightness control circuit using a differential clipper one input to which supplied with a reference voltage and the other input to which is derived from the output of the green final amplifier stage to cause a comparison of the blackest-going signal during each trace interval. The output of the differential clipper is supplied to a second integrating circuit, the outpt of which is used to vary the DC operating level of the green, blue and red driver amplifiers to form a closed loop control system. Thus, the blackest level of the signal passing through the green amplifier stage is chosen as black for the brightness control circuit and the black level of the receiver is automatically adjusted accordingly.
Inventors
- 👤 Ernest C Macintyre Jr
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-04 06:49
CPC Classifications
H; H04; H04N; H04N5/00; H04N5/44; H04N5/57; H04N5/58
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
206 words
In a television receiver comprising a cathode-ray tube, a source of video signals, and a circuit including a video amplifier for coupling the source of video signals to the cathode-ray tube including in combination: light responsive means for providing an output voltage indicative of the amount of ambient light impinging on said light responsive means, said light responsive means being physically located to receive ambient light impinging upon the television receiver; a field-effect transistor having at least a gate electrode and an output electrode, with the gate electrode coupled to receive the output voltage from said light responsive means; a lamp; means coupling the output electrode of said field-effect transistor in series with said lamp to vary the intensity of the light produced by said lamp in accordance with variations in the conductivity of the field-effect transistor; a light dependent resistor located to receive only the light emanating from said lamp, with the resistance of said light dependent resistor varying in accordance with the light impinging 01 thereon; and means coupling said light dependent resistor in series circuit with said video amplifier so that the signals obtained from the output of said video amplifier are attenuated in accordance with the resistance of said light dependent resistor.
Claim 2
Dependent Claim
206 words
In a television receiver comprising a cathode-ray tube, a source of video signals, and a circuit including a video amplifier for coupling the source of video signals to the cathode-ray tube including in combination: light responsive means for providing an output voltage indicative of the amount of ambient light impinging on said light responsive means, said light responsive means being physically located to receive ambient light impinging upon the television receiver; a field-effect transistor having at least a gate electrode and an output electrode, with the gate electrode coupled to receive the output voltage from said light responsive means; a lamp; means coupling the output electrode of said field-effect transistor in series with said lamp to vary the intensity of the light produced by said lamp in accordance with variations in the conductivity of the field-effect transistor; a light dependent resistor located to receive only the light emanating from said lamp, with the resistance of said light dependent resistor varying in accordance with the light impinging 01 thereon; and means coupling said light dependent resistor in series circuit with said video amplifier so that the signals obtained from the output of said video amplifier are attenuated in accordance with the resistance of said light dependent resistor.
Claim 3
Dependent Claim
41 words
The combination according to claim 15 wherein the light responsive means includes a voltage divider connected across a source of DC potential, with at least a portion of the voltage divider being in the form of a second light dependent resistor.
Claim 4
Dependent Claim
26 words
The combination according to claim 1 further including an integrating time delay circuit coupled between the light responsive means and the gate of the field-effect transistor.
Claim 5
Dependent Claim
27 words
The combination according to claim 2 further including a resistance-capacitance integrating circuit connected between the output of said voltage divider and the gate of said field-effect transistor.
Claim 6
Dependent Claim
190 words
In a television receiver having a cathode-ray tube, a source of video signals comprising at least brightness components and a circuit including a video amplifier for coupling the brightness signal components to the cathode-ray tube, an automatic contrast control circuit for the brightness components of the video signal including in combination: a first lIght dependent resistor connected in a voltage divider circuit connected across a source of DC potential and physically located to be responsive to the ambient light impinging upon the television receiver; a voltage variable conductive device connected in series with a source of DC potential; circuit means coupling an output on the voltage divider to the voltage variable conductive device for controlling the conduction thereof; a lamp connected in series with the variable conductive device for receiving varying amounts of current therefrom to produce a varying intensity of light in accordance with the amount of current flowing therethrough; a second light dependent resistor arranged to be illuminated only by the light emanating from the lamp; and means connecting the second light dependent resistor in series with the video amplifier for attenuating the output of the video amplifier.
Claim 7
Dependent Claim
190 words
In a television receiver having a cathode-ray tube, a source of video signals comprising at least brightness components and a circuit including a video amplifier for coupling the brightness signal components to the cathode-ray tube, an automatic contrast control circuit for the brightness components of the video signal including in combination: a first lIght dependent resistor connected in a voltage divider circuit connected across a source of DC potential and physically located to be responsive to the ambient light impinging upon the television receiver; a voltage variable conductive device connected in series with a source of DC potential; circuit means coupling an output on the voltage divider to the voltage variable conductive device for controlling the conduction thereof; a lamp connected in series with the variable conductive device for receiving varying amounts of current therefrom to produce a varying intensity of light in accordance with the amount of current flowing therethrough; a second light dependent resistor arranged to be illuminated only by the light emanating from the lamp; and means connecting the second light dependent resistor in series with the video amplifier for attenuating the output of the video amplifier.
Claim 8
Dependent Claim
31 words
The combination according to claim 5 wherein the lamp and the second light dependent resistor both constitute parts of a light shielded isolator package and are electrically isolated from one another.
Claim 9
Dependent Claim
52 words
The combination according to claim 5 further including an integrating circuit included in the circuit means for controlling the conduction of the variable conductive device, said integrating circuit operating to cause said control to be responsive only to the average intensity of the ambient light impinging upon the first light dependent resistor.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1974-11-22 | 1975-05-24 | 1975-11-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1978-11-22 | 1979-05-24 | 1979-11-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1982-11-22 | 1983-05-24 | 1983-11-23 | $7700.00 | Window Closed / Lapsed |