Device for receiving closed captioned broadcasts

Abstract

A synchronizing/separator circuit separates a horizontal synchronizing signal and a vertical synchronizing signal contained within a television signal. A phase locked loop synthesizes a clock signal at 32 fH by phase locking the horizontal synchronizing signal with a divided version of the 32 fH clock signal. The phase locked loop includes a voltage controlled oscillator (VCO) responsive to the phase comparison to perform the phase lock. A circuit separates the run-in clock and caption data in horizontal scanning period 21 H in the vertical blanking interval. A phase comparator receives the run-in clock and phase compares it with the 32 fH clock to produce an alternating control signal which is applied directly to the voltage controlled oscillator for rapid phase locking of the voltage controlled oscillator in preparation for decoding the caption data. The voltage controlled oscillator is controlled by the charging and discharging rate of a capacitor charged by a constant current source. The control signal varies the charging and discharging rate of the capacitor to effect rapid phase lock to the run-in clock.