JPS5959046U - Television broadcast signal discrimination circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing one embodiment of this invention, FIG. 2 is an output characteristic diagram of the AFT circuit of FIG. 1, and FIG. 3 is a configuration explanatory diagram specifically showing the control circuit of FIG. 1. Figure 4 is a flowchart shown to explain the operation of the circuit in Figure 3, and Figures 5a, -b, and c are also output signal waveform diagrams shown to explain the operation of the circuit in Figure 3. It is. - 11... Voltage controlled oscillator, 12... Programmable frequency divider, 17... Control circuit, 22... AF
T circuit, 35... central processing unit (cpu), 36
...Read only memory (ROM), 37... Arithmetic circuit, 40... Clock pulse generation circuit, 41...
・Speed switching /17 /16 □ Figure 2 VAFT J−−+−” and −111−−゛

Claims (2)

[Scope of utility model registration request] (1) So that the tuning operation of one channel by the tuning means is brought to a tuning completion state by detecting the presence of both the video carrier wave and the audio carrier wave of that channel.
A television broadcast signal discriminating circuit characterized by comprising a means for confirming the video carrier wave and the audio carrier wave, which operates during a channel selection operation. (2) The tuning means includes a phase-locked loop that can vary the oscillation frequency of the voltage-controlled oscillator by adding division ratio data to a division-ratio control end of the programmable frequency divider, and the voltage-controlled oscillator. and a mixer to which the oscillation output of the oscillator is added, and the means for confirming the video carrier wave and the audio carrier wave includes:
Automatic fine tuning in which the output obtained from the mixer is input, and if the intermediate frequency to be input is below a specified frequency, a first detection output is obtained, and if it is higher than the specified frequency, a second detection output is obtained. and a circuit that, upon input of channel selection data for channel designation, emits the frequency division ratio data such that the frequency reception state is lower than the broadcasting standard frequency of the designated channel, and divides the frequency division ratio of the programmable frequency divider. a first means for applying the frequency division ratio data to the frequency ratio control terminal; and a first means for presetting the frequency division ratio data generated by the first means in a presettable up/down counter to vary the data value at the frequency division ratio control terminal. and a third means for detecting that the first detection output and the second detection output are obtained from the automatic fine tuning circuit by varying the data value of the second means. and a frequency division ratio of the programmable frequency divider such that when the second detection output is detected by the flexible third means, the reception state is set to the frequency at which the audio carrier wave of the specified channel is present. a fourth means for changing the frequency division ratio data applied to the control terminal; The third means and stage return the data of the frequency division ratio control terminal to the frequency division ratio data at the time when the second detection output was obtained, and the presettable up/down counter is operated until the second detection output is no longer obtained. The television broadcast signal discriminating circuit according to claim 1, further comprising fifth means for controlling in a direction opposite to the previous one.