Signal generator circuit

Abstract

A signal generator circuit for a television receiver employed in a videotex or CAPTAIN system comprises a reference signal oscillator for producing a reference signal and a synchronizing signal generator for generating a horizontal synchronization signal synchronized with the reference signal. A frequency divider is responsive to the reference signal for producing a color sub-carrier signal. A phase-locked loop is responsive to the sub-carrier signal and includes a voltage-controlled oscillator. The voltage-controlled oscillator produces an output signal synchronized with the sub-carrier signal and having a series of rising edges. A rising edge of the sub-carrier signal periodically coincides with a rising edge of the signal from the voltage-controlled oscillator. A detector detects a time when a rising edge of the sub-carrier signal coincides with a rising edge of the output signal of the voltage-controlled oscillator, and a clock signal is then generated synchronized with the output signal of the voltage-controlled oscillator and having a series of falling edges. The horizontal synchronization signal generator and the clock signal generator are controlled so as to ensure that the rising edge of the horizontal synchronization signal coincides with a falling edge of the clock signal. This ensures an accurate count of the pulses for determining the horizontal position of a display by the receiver and prevents horizontal jitter in the display.