Burst gating signal generating circuit
AssigneeGTE Products Corporation
InventorJohn D. Lovely
Life of this patent
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Abstract
A circuit for generating an accurately-timed noise-free signal for gating the chrominance burst portion of the composite video signal. The horizontal sync pulses are differentiated and clamped to the horizontal blanking pulses. The output pulses are then applied to a gating diode that is conductive only when those pulses have an amplitude above a predetermined bias level. The resultant pulses are coupled to the input of a burst gate so that the gate is open only for a period of time substantially coterminous with the burst period. The burst gate is thereby rendered immune to noise signals occurring during the active line period and the accuracy of the gating signal is independent of the television receiver's horizontal time base.
Claims16
A burst gating signal generating circuit comprising:
- first means having a first input coupled to a source of horizontal sync pulses and a second input coupled to a source of horizontal blanking pulses, said means for providing at its output differentiated sync pulses;
- clamping means coupled between the source of blanking pulses and the output of the first means for providing combined pulses including differentiated sync pulses clamped and added to the horizontal blanking pulses;
- a bias supply;
- gating means coupled between the output of the first means and the bias supply for providing resultant pulses corresponding to those portions of the combined pulses having an amplitude greater than a predetermined amplitude related to the value of the bias supply, and
- second means coupled between the gating means and the burst gate circuit for removing the DC component of the resultant pulses.
A burst gating signal generating circuit comprising:
- a differentiating circuit having an output, a first input coupled to a source of horizontal sync pulses and a second input coupled to a source of horizontal blanking pulses;
- a clamping circuit coupled between the source of horizontal blanking pulses and the output of the differentiating circuit so that combined pulses appear at the output of the differentiating circuit, said combined pulses including differentiated sync pulses clamped and added to the horizontal blanking pulses;
- a gating circuit coupled to the output of the differentiating circuit for passing only those portions of the combined pulses of an amplitude greater than a predetermined amplitude;
- and
- means for coupling the output of the gating circuit to the burst gate circuit.
A method of generating a burst gating signal comprising the steps of:
- (a) differentiating horizontal sync pulses;
- (b) clamping differentiated horizontal sync pulses of one polarity to the horizontal blanking pulses;
- (c) adding differentiated horizontal sync pulses of the opposite polarity to the horizontal blanking pulses;
- (d) gating only those portions of the clamped and added horizontal sync and blanking pulses in excess of a predetermined value;
- (e) coupling the gated pulses to the burst gate circuit.
Dependencies are inferred from the claim text.