JPS57193131A - Television channel selecting device - Google Patents

Abstract

PURPOSE:To make circuit integration for a TV tuner and to achieve no adjustment in the manufacturing process, by providing a phase locked loop synchronizing the phase of an output of a voltage controlled local oscillator with the phase of one video carrier wave in high frequency input section outputs. CONSTITUTION:A voltage controlled local oscillator 2 generates a frequency near the video carrier wave frequency of a desired station for channel selection inputted to a high frequency input section 1 with a frequency synthesizer comprising the 2nd PLL circuit consisting of a prescaler 13, a variable frequency divider 14, a phase comparator 15, an LPF 16, a reference oscillator 17, a reference frequency divider 18 and an analog switch ASW 12. Further, the 1st PLL circuit consisting of a 90 deg. phase shifter 6, a mixer 7, a signal LPF 8, a signal amplifier 9, a phase comparator 10, an LPF 11, and an ASW 21 controls the frequency and phase of the oscillator 2 equal to the video carrier wave frequency and phase respectively, and the mixer 3 makes synchronous detection for the video carrier wave to constitute the synchronous reception state converted into an intermediate frequency to the audio carrier wave. Thus, circuit integration can be much easier in comparison with tuners of conventional types using inductance and no adjustment can be realized.