JPH0223116U - - Google Patents

Description

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the AFT correction circuit according to the present invention, FIG. 2 is a flowchart for explaining the operation of the circuit in FIG. 1, and FIG. 3 is another embodiment of the present invention. 4 is a block diagram showing a conventional AFT correction circuit, and FIGS. 5, 6, and 7 are flowcharts for explaining the operation of the conventional AF
Graphs for explaining the characteristics of the AFT correction operation in the T correction circuit, and FIGS. 8, 9, and 10 are graphs for explaining the problems of the conventional AFT correction circuit. 1... Antenna, 2... Chuyuna, 3... PI
F amplifier circuit, 4...Video detection circuit, 5...Band switching circuit, 7...AFT circuit, 8...Low pass filter, 9...Synchronization separation circuit, 10...Microcomputer, 11...Horizontal synchronization separation output presence/absence Judgment circuit, 12
...AFT up/down determination circuit, 13...Mode and channel switching device, 16...Key input circuit, 17...Band judgment circuit, 18...Band switching signal generation circuit, 19...Control voltage switching circuit, 2
0 to 22, 24, 25, 28, 29...AND circuit, 23, 26, 27...Inverter, 30, 3
1...OR circuit, 32...AFT correction signal output circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] It is possible to receive a television signal in which the frequency relationship between the video carrier wave and the audio carrier wave is reversed between the VHF low band and other bands,
a tuner having a local oscillation circuit whose local oscillation frequency is adjusted by a control voltage, and converting an introduced RF video signal into a video intermediate frequency signal and outputting the same;
an AFT circuit that outputs an AFT signal based on the difference between the frequency of the video intermediate frequency signal and a predetermined video intermediate frequency, and provides a control voltage based on the AFT signal to the local oscillation circuit to generate a local The AFT correction circuit that adjusts the oscillation frequency includes a band determination circuit that outputs a first determination signal indicating whether or not a receiving channel is a VHF low band, and a synchronous separation circuit that determines the presence or absence of a signal on the receiving channel. A signal presence/absence determination circuit that makes a determination based on the output and outputs a second determination signal that exhibits a different level depending on the presence or absence of the signal;
an AFT up-down determination circuit that outputs a third determination signal indicating whether it is an FT up signal or a lowered AFT down signal; In a state where the determination signal indicates that the VHF low band
The down signal is outputted based on the second determination signal, the AFT up signal exhibits a first pull-in condition that is outputted independently of the second determination signal, and the first determination signal is output in a range other than VHF low band. In the state indicating the band, the AF of the third determination signal is
a condition setting means configured to exhibit a second pull-in condition in which the T-up signal is output based on the second determination signal and the AFT-down signal is output regardless of the second determination signal; An AFT correction circuit comprising control voltage generating means for generating the control voltage by introducing an output from the means.