JPS57174988A - Television receiver - Google Patents

Abstract

PURPOSE:To prevent the disorder of a display screen and the generation of an uncomfortable sound during channel selection by sweeping all broadcasting channels automatically by employing a frequency synthesizer system, and storing channels where signals are present by scanning all broadcasting channels when a power source is put to work. CONSTITUTION:A desired broadcasting channel number is inputted from an input part 11, and a key input from the input part 11 is processed by a control part 12 to generate the frequency division ratio data of a PLL circuit part. A channel selection part 13 inputting said frequency division ratio data is equipped with the PLL circuit part consisting of a reference frequency oscillator 1a, a phase comparator 2a, an LPF3a, a VCO4a, and a frequency divider 5a. A signal detecting circuit 15, on the other hand, detects the presence of signals in broadcasting channels changed successively, and information on whether a signal is present or not is applied to the control part 12 to store the frequency division ratio data in a storage circuit 17. When a power source detecting circuit 14 detects a power source being turned on, all channels are swept and the channel selection part 13 is controlled by the frequency division ratio data stored in the circuit 17 to prevent the disorder of a display screen and the generation of an uncomfortable sound.