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Color eliminating circuit
| Details |
Inventors: Tanihara, Yozo; Niimi, Masayasu;
Assignee: Hitachi, Ltd. (JA)
Primary Examiner: Mayer; Albert J.
Assistant Examiner: Saffian; Mitchell
Attorney, Agent or Firm: Craig & Antonelli
A color eliminating circuit comprises a killer detection circuit, a band amplifier circuit and a control circuit. The killer detection circuit detects a color burst signal in a chromatic signal applied to an input thereof, and delivers a killer output voltage to the band amplifier circuit. When the killer output voltage is higher than a predetermined operating voltage of the band amplifier circuit, the band amplifier circuit amplifies the chromatic signal supplied thereto; when the killer voltage is lower than the operating voltage, the band amplifier circuit does not amplify the chromatic signal. The control circuit provides a gate pulse for the detection of the color burst signal, which pulse is applied to a further input of the killer detection circuit. When the killer voltage is below the operating voltage of the band amplifier circuit, the control circuit interrupts the provision of the gate pulse, to prevent the killer voltage from being supplied from the killer detection circuit. Thus, where the field strength of received signals is extremely low, an increase in the killer voltage due to noise, which might inadvertently operate the band amplifier circuit, is avoided. |
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DETAILED DESCRIPTION What we claim: 1.
A color eliminating circuit for use in a color television system comprising: an amplifier circuit for gating a color signal and subjecting the color signal to controlled amplification; a killer detection circuit, connected to said amplifier circuit, for controlling the action of gating and amplification of said amplifier circuit; and means, connected to said killer detection circuit and responsive to the level of a received color signal, for causing said killer detection circuit to cut-off the operation of said amplifier circuit when either the level of a received color signal fails to exceed a prescribed level or in the absence of receiving a color signal and the killer detection output of said killer detection circuit exceeds a prescribed operating voltage of said amplifier circuit.
2.
A color eliminating circuit according to claim 1, wherein said means comprises a control circuit which generates a pulse for causing said killer detection circuit to extract a color burst signal from the color signal in response to the level of the color burst component of said color signal reaching a prescribed level.
3.
A color eliminating circuit according to claim 2, wherein said control circuit includes a differential amplifier circuit having first and second inputs and an output, said first input being connected to receive a selected DC voltage level, said second input being connected to receive a signal representative of the level of said color burst component, and said output being coupled to a control terminal of said killer detection circuit.
4.
A color eliminating circuit according to claim 3, wherein said control circuit further includes summing means, connected to the second input of said differential amplifier circuit, for obtaining the sum of a pulse signal synchronized with said color burst component and a signal representative of the level of said color burst component, and means for supplying said sum to the second input of said differential amplifier circuit
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TV Signal 
