Ramp comparator arrangement useful in an on-screen channel indic

Details Ramp comparator arrangement useful in an on-screen channel indic Ramp comparator arrangement useful in an on-screen channel indic

1984-01-23

1986-07-01

Groody, James J.

Facsimile and static presentation processing

Facsimile

Specific signal processing circuitry

3581911, 3581931, 307362, H04N 550

Patent

active

045983178

ABSTRACT:
A television receiver includes a tuner responsive to a tuning voltage generated by a signal seeking tuning control unit and a channel indicator for displaying a vertical bar on the screen of the picture tube. The horizontal position of the bar is determined by the magnitude of the tuning voltage. The channel indicator includes a ramp signal generator for generating a composite ramp signal including a horizontal deflection rate ramp signal superimposed on the tuning voltage, a first AND function gate acting as a comparator to generate a first transition when the amplitude of the composite ramp signal traverses a switching threshold, a differentiator for determining the width of the bar having an input coupled to the output of the first AND function gate and an output coupled to a second AND gate which selectively couples the output signal of the differentiator to the picture tube when it is desired to display the bar. The two AND function gates are included in the same integrated circuit and, therefore, the output signal of the second AND function gate may be coupled to the first AND function gate to cause it to falsely switch thereby producing a disconcerting second bar on the screen. To overcome this problem, a feedback network is coupled between the output of the differentiator and a second input of the first AND gate to disable it from generating a second transition for a predetermined time after the first transition.

REFERENCES:
patent: 4204173 (1980-05-01), Aschwanden
patent: 4366502 (1982-12-01), Shiu
Pages 405-408 of the book "Pulse, Digital, and Switching Waveforms, Devices, and Circuits for their Generation and Processing" by J. Millman and H. T. Taub, published by McGraw-Hill Book Company, 1965.
A portion of the schematic for Hitachi CK-200.

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