United States Patent (19) 11) 4,287,530 Gay Et Al
United States Patent (19) 11) 4,287,530 Gay et al. (45) Sep. 1, 1981 54 DEMODULATOR SYSTEM INCLUDING A nance information signals from the frequency modu TUNABLE DISCRIMINATOR SUITABLE lated Secam RF subcarrier frequencies without the FOR USE IN A SECAM TELEVISION necessity for precise and stable tuned circuits. The de RECEIVER modulating system includes a single discriminator hav 75 Inventors: Michael J. Gay, Chancy; Johannes A. ing an electronically tunable center frequency, a Gutmann, Geneva, both of remodulator, for producing a reference frequency am Switzerland plitude modulated by the chrominance information (73) Assignee: Motorola Inc., Schaumburg, Ill. signals which are supplied to a commutator as known, and a feedback circuit coupled between the discrimina 21 Appl. No.: 148,347 tor and remodulator. The discriminator is selectively 22 Filed: May 9, 1980 tuned to a reference center frequency during each pic ture line clamp period to produce a zero level output 51) Int. Cl. ............................................... H04N 9/50 signal. During the chrominance information portion of I52) U.S. Cl. ...................................................... 358/23 each line, the center frequency of the discriminator is 58) Field of Search ............................. 358/23; 329/50 alternately offset by first and second control signals to 56 References Cited center frequencies coinciding with the two reference U.S. PATENT DOCUMENTS frequencies to produce a zero output level whenever the Secam signals are at the respective RF subcarrier 3,806,632 4/1974 Okada .................................... 358/23 frequencies. The feedback circuit ensures that the zero 4,232,268 ll/1980 Hinn ....................................... 358/23 output levels obtained during the information carrying Primary Examiner-Richard Murray portion of each line is identical with the zero output Attorney, Agent, or Firm-Michael D.
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