US3755618A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Shunt color killer circuit
Assignee: Zenith Electronics LLC
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Filing: 1972-03-02
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Granted: 1973-08-28
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Expires: 1992-03-02
Abstract
Abstract A color killer circuit is provided for disabling the chrominance processing channel when the signal strength of the received chrominance signals drops below a selectable, predetermined level. The circuitry, which is suitable for fabrication on a monolithic integrated circuit, includes a semiconductor arrangement coupled in shunt with a differential amplifier between a source of unidirectional potential (B+) and the output of a chroma driver amplifier. Whenever the chrominance signal strength is at or above the selectable, predetermined level indicative of normal color reception, the chroma driver, responsive to chrominance signals applied at its input, develops a chrominance-modulated current which is conducted through the differential amplifier to the chroma demodulator. On the other hand, whenever the chrominance signal strength is below the selectable, predetermined level, the semiconductor arrangement is switched to its conductive state by a control network in response to control signals representative of the chrominance signal strength. In its conductive state, the semiconductor arrangement presents an alternate low impedance current path to the chrominance-modulated current diverting it from the differential amplifier and thereby preventing chroma reproduction.
Inventors
- 👤 D Poppy
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 14:26
CPC Classifications
H; H04; H04N; H04N9/00; H04N9/64; H04N9/70; H04N9/71
Claims Analysis
Total Claims: 8
Claim 1
Independent Claim
152 words
In a television receiver having chrominance amplifier means, coupled to a B+ reference potential for amplifying chrominance signals derived from received television signals, said chrominance amplifier means developing chrominance modulated current from said chrominance signals; and including means for developing control signals indicative of chrominance signal reception, a color killer circuit comprising in combination: shunt means coupled between said B+ reference potential and said chrominance amplifier means, said shunt means comprising a transistor switch having an input circuit and an output circuit coupled across the output of said chrominance amplifier means, said shunt means being normally non-conductive and being conditionable to a conductive state for shunting the output of said chrominance amplifier means; and control means including a source of second reference potential establishing a threshold coupled to the input circuit of said shunt means for switching said shunt means into said conductive state responsive to said control signals reaching said threshold.
Claim 2
Dependent Claim
152 words
In a television receiver having chrominance amplifier means, coupled to a B+ reference potential for amplifying chrominance signals derived from received television signals, said chrominance amplifier means developing chrominance modulated current from said chrominance signals; and including means for developing control signals indicative of chrominance signal reception, a color killer circuit comprising in combination: shunt means coupled between said B+ reference potential and said chrominance amplifier means, said shunt means comprising a transistor switch having an input circuit and an output circuit coupled across the output of said chrominance amplifier means, said shunt means being normally non-conductive and being conditionable to a conductive state for shunting the output of said chrominance amplifier means; and control means including a source of second reference potential establishing a threshold coupled to the input circuit of said shunt means for switching said shunt means into said conductive state responsive to said control signals reaching said threshold.
Claim 3
Dependent Claim
73 words
A color killer circuit in accordance with claim 1 wherein said threshold is established by a diode having a first electrode coupled to the input of said shunt means and a second electrode coupled to said source of second reference potential for determining the conduction threshold of said transistor switch, said diode being effective to switch said shunt means into said conductive state whenever the level of said control signals crosses said threshold.
Claim 4
Dependent Claim
44 words
A color killer circuit in accordance with claim 2 wherein said means for developing control signals indicative of chrominance signal reception include a variable impedance for selecting a predetermined level of said control signals to represent a desired signal strength of said chrominance signals.
Claim 5
Dependent Claim
88 words
A color killer circuit in accordance with claim 1 wherein said chrominance amplifier means includes a chrominance output stage and wherein said transistor switch comprises first and second transistors, said first transistor having a collector-emitter junction interconnected between said B+ reference voltage and the base electrode of said second transistor and said second transistor having a collector-emitter junction coupled to said B+ reference potential across said chrominance output stage, said source of second reference potential comprising a diode coupled directly to said base electrode of said first transistor.
Claim 6
Dependent Claim
70 words
A color killer circuit in accordance with claim 1 wherein said chrominance amplifier means includes first and second chrominance amplifiers, said second chrominance amplifier comprising driver means coupled to said first chrominance amplifier and differential amplifier means coupled to said driver means for amplifying said chrominance-modulated current said said shunt means being coupled between said B+ reference potential and the junction of said driver means and said differential amplifier means.
Claim 7
Dependent Claim
42 words
A color killer circuit in accordance with claim 5 wherein said driver means comprises a transistor having a base electrode coupled to said first chrominance amplifier, an emitter electrode coupled to ground and a collector electrode coupled to said differential amplifier means.
Claim 8
Dependent Claim
95 words
A color killer circuit in accordance with claim 5, further including chroma gain control means, and wherein said differential amplifier means comprises third and fourth transistors having interconnected emitter electrodes coupled to said driver means, said third transistor having a collector electrode coupled to said B+ reference potential and said fourth transistor having a collector electrode serving as an output for a chroma demodulation system, said third and said fourth transistors having respective base electrodes coupled to said chroma gain control means for varying the level of said chrominance-modulated current conducted through said fourth transistor.
References Cited (Backward Citations)
US3604842A
Cited
US3626089A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-08-27 | 1977-02-26 | 1977-08-28 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-08-27 | 1981-02-26 | 1981-08-28 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-08-27 | 1985-02-26 | 1985-08-28 | $7700.00 | Window Closed / Lapsed |