Abstract: A data and synchronization extraction circuit for processing composite video signals containing closed captioning data is disclosed. A dual mode voltage clamp is realized in CMOS technology which includes temperature compensated current sources in the form of complementary current mirrors. A modified version of such current sources is also disclosed which permits trimming of the current after manufacture and packaging. Sync pulses are separated by doubling the amplitude of a composite video signal with an amplifier and comparing the amplified signal with a back porch level derived by a sample-and-hold device. Frequency and phase synchronization is accomplished by a combination of a frequency lock loop and a phase lock loop working in concert to generate a control voltage for a voltage controlled oscillator in a flywheel mode. The voltage controlled oscillator provides a clean source of timing information for the circuit.
Type:
Grant
Filed:
March 2, 1992
Date of Patent:
April 4, 1995
Assignees:
EEG Enterprises, Inc., Extratek, Inc.
Inventors:
Eric B. Berman, Apparajan Ganesan, William B. H. Jorden, Philip R. McLaughlin, William Posner