H - Electricity – 04 – N
Patent
H - Electricity
04
N
H04N 5/455 (2006.01) H03D 1/22 (2006.01) H03D 3/00 (2006.01) H04L 27/02 (2006.01) H04N 5/50 (2006.01) H04N 5/44 (2006.01) H04N 7/24 (2006.01)
Patent
CA 2178198
A synchronous demodulator is controlled by a phase locked loop for tuning to a pilot in a television signal. A start-up interval is commenced upon initiation of tuning (either after power-up or a channel change) during which a substitute signal at the pilot frequency is supplied to the phase locked loop to rapidly bring the VCO close to its lock- up frequency. Thereafter the IF signal is supplied. The start-up interval is defined by an AFC Defeat signal from a microprocessor and controls an IF switch. The substitute signal is from a crystal oscillator.
Démodulateur synchrone qui est commandé par une boucle à verrouillage de phase afin de régler l'accord avec une onde pilote dans un signal de télévision. Un intervalle de démarrage débute au commencement du réglage d'accord (soit après mise sous tension, soit après changement de chaîne) pendant lequel un signal de substitution à la fréquence de l'onde pilote est appliqué à la boucle à verrouillage de phase pour amener rapidement l'oscillateur commandé en tension près de sa fréquence de verrouillage. Ensuite, le signal FI est fourni. L'intervalle de démarrage est défini par un signal d'invalidation CAF provenant d'un microprocesseur et commande un interrupteur FI. Le signal de substitution est émis par un oscillateur à quartz.
Krishnamurthy Gopalan
Mycynek Victor G.
Sgrignoli Gary J.
Marks & Clerk
Zenith Electronics Corporation
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