Zenith Electronics Corporation

Zenith Radio Corporation

Stan Bart

Gopal K Srivastava

George J Tzakis

A novel method and apparatus of AC coupling composite video sync information to a sync separator circuitry with digital controlled filtered DC feedback is described. An AC coupling circuit such as a capacitor provides an intermediate signal in response to received composite video. The intermediate signal may be level adjusted and gain provided to provide a first input to a sync slicer and an input to a sync filter. The output of the sync filter may provide a second input to the sync slicer circuit which responsively varies the reference level for the sync slicer in repsonse to variations in the level of the received composite video. DC feedback from the filter to the AC coupling circuit provides for a stabilization in the intermediate signal and in the filter output signal. These two signals ultimately provide the input to the sync slicer so that the composite sync is provided in response to all sync signals in spite of level variations in the sync tips in the received composite video signal.

AC coupled sync separator system with filter DC feedback

Composite sync is separated from video despite noisy, weak, or nonstandard signal conditions. Sync is separated from the composite video signal by comparing the video signal to a D.C. reference voltage which is generated depending upon the particular characteristics of the received video signal. Outputted sync signals during vertical sync and nonstandard periods are conditioned for proper phasing in other receiver circuits such as the Horizontal A.P.C.

Digital sync separator and differentiator

A ramp generator is described for developing a ramp voltage for use in vertically deflecting the electron beam or beams of a television receiver. The ramp generator receives a vertical rate pulse developed by the receiver for developing a charging current during the occurrence of the vertical rate pulse. A discharging current is also generated, and both currents are applied to a capacitor for developing a ramp voltage which increases and then decreases in amplitude. A clamp circuit in the generator is enabled when the vertical pulse is received for clamping the ramp voltage on the capacitor to a predetermined peak voltage via low impedance path such that unwanted voltage components are substantially eliminated from the ramp voltage during the clamping action.

Vertical ramp generator for a television receiver

A pulse width modulator is described for width-modulating horizontal rate pulses developed in a television receiver and for applying the width-modulated pulses to the receiver's horizontal drive system. In the illustrated embodiment, the modulator includes a differential amplifier which senses the receiver's high voltage and beam current to develop a control signal which varies in accordance with variations in the beam current and the high voltage. A second differential amplifier receives the control signal and horizontal rate pulses for developing pulses whose width is varied in response to variations in the control signal. The width-modulated pulses cause the horizontal drive system to generate a substantially constant horizontal picture size despite variations in line voltage and brightness.

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Hoffman Estates, IL, United States of America

Stan Bart