JPH0563514A - Tuning device - Google Patents

Abstract

PURPOSE:To keep a stable reception state in a usual reception by controlling an electronic tuner with a pulse width modulation signal at searching and with the data of a local oscillating frequency stored in a memory at a usual reception respectively so as to allow the tuner to tune immediately even a non-standard broadcast. CONSTITUTION:A microcomputer 1 applies a pulse width modulation wave PWM to a local oscillator 3 as a tuning voltage via an LPF 2 at channel searching. Thus, the local oscillation frequency is varied continuously and when a broadcast station reaches a tuning point, the microcomputer 1 stores a value resulting from counting the local oscillating frequency of the tuner 11 at this time into a memory 9. The tuning data are stored in the memory 9 through the repetitive operation and preset is finished. Then the reception is attained and PLL data are read from the memory 9 at the normal reception and fed to a PLL circuit 10. The frequency division ratio of a variable frequency divider is changed in the circuit 10 and a tuning voltage obtained thereby is supplied to the oscillator 3 of the tuner 11 for the tuning. Thus, the tuner immediately tunes to a CATV at searching and stable reception state is kept even in the usual reception.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver,
The present invention relates to a channel selection device used for a video tape recorder or the like.

[0002]

2. Description of the Related Art As a channel selection device for a television (TV) receiver, a video tape recorder (VTR), etc., a voltage synthesizer system and a frequency synthesizer system are generally used.

In the voltage synthesizer system, the tuning operation of the tuner is performed by applying a DC voltage, and in this system, even if the frequency of the broadcast to be received is unknown, it can be selected by the search operation.

[0004]

However, the voltage synthesizer type tuning device has a drawback that it is not possible to sufficiently correct the drift of the local oscillation frequency due to the fluctuation of the ambient temperature and the voltage.

On the other hand, in the frequency synthesizer type channel selecting apparatus, since the local oscillation frequency is constantly controlled by the PLL (Phase Locked Loop) circuit, the above drift does not occur.

However, in the frequency synthesizer type channel selecting device, even if a broadcasting station whose frequency is unknown is to be searched and tuned, only the frequency programmed in advance in the channel selecting microcomputer (microcomputer) can be output. , It is not possible to tune to a broadcasting station that deviates from the frequency output from the microcomputer. For this reason, it is conceivable to subdivide the frequencies to be searched, but in that case it takes too much time to search all the frequencies.

Accordingly, the present invention is directed to overcoming such drawbacks.

[0008]

The tuning device of the present invention applies a pulse width modulation signal from a microcomputer to a variable capacitance element of an electronic tuning tuner through a low pass filter when searching a broadcasting station. A search operation is performed, and as the tuning point data obtained by the search operation, a value obtained by counting the local oscillation frequency of the tuner at that time is stored in a memory, and when tuning, the tuner is based on the data stored in the memory. The local oscillation frequency is controlled.

[0009]

According to the above construction, the electronic tuning tuner is controlled by the pulse width modulation signal at the time of search, and at the time of normal reception, the local oscillation frequency data stored in the memory is used.
The configuration is such that the tuner is controlled.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram of a channel selecting device embodying the present invention, where 1 is a microcomputer, 2 is an LPF (converting a pulse width modulated wave (PWM) signal output from the microcomputer 1 into a DC voltage). Low pass filter), 3 is the LPF
A local oscillator (OSC) whose oscillation frequency changes when a DC voltage from 2 is applied to the variable-capacitance diode 3a of the electronic tuning tuner 11 is an R from an antenna.
It is a mixer for mixing the F signal and the local oscillation frequency of the OSC.

Reference numeral 12 is an IF block, and the IF signal from the tuner is applied to the detection circuit 5 of the IF block 12. The detection circuit 5 detects this and supplies the video signal obtained thereby to the sync separation circuit 6. The sync separation circuit 6 extracts the horizontal sync signal and supplies it to the microcomputer. The output of the detection circuit 5 is also applied to the AFT circuit 7, and the AFT / S-curve voltage obtained from the AFT circuit 7 is supplied to the microcomputer 1. Reference numeral 9 is a memory for storing various data. Reference numeral 8 is a prescaler for dividing the output of the local oscillator, and 10 is a PLL circuit to which the output of the prescaler 8 is input.

Next, the operation will be described. (At the time of searching) At the time of searching, the microcomputer 1 applies the PWM signal to the local oscillator as a tuning voltage via the low-pass filter 2. As a result, the local oscillation frequency can be continuously varied, and the reception frequency can be changed as a result. However, when the broadcasting station reaches a certain point (tuning point), the microcomputer receives a predetermined sync signal and AFT · S signal. Since a curved curve voltage is supplied, when the microcomputer determines that there is a tuning point or locality based on these signals when it receives these signals, it temporarily stops the search operation and the microcomputer determines the frequency from the prescaler at this time. Counting, the microcomputer 1 creates PLL data (data for determining the frequency division ratio) based on the counted data, and stores it in the memory 9. The preset operation is completed when a predetermined tuning data is stored in the memory by repeating such an operation. (At the time of normal reception) When the preset operation is completed, reception is possible. At the time of normal reception, the PLL data is read from the memory 9 and supplied to the PLL circuit 10. The PLL circuit 10 is composed of a well-known PLL circuit, the frequency division ratio of the variable frequency divider is changed based on the PLL data, and the tuning voltage obtained by this is supplied to the local oscillator 3 of the tuner 11 to be selected. Bureau is made. In addition, during this normal reception, the PWM from the microcomputer 1
It goes without saying that no signal is output.

[0014]

As described above, according to the present invention, it is possible to immediately tune to a non-standard broadcasting frequency such as CATV at the time of searching, and in the normal receiving state, there is no deviation of the local oscillation frequency and stable reception is possible. I can keep the state.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a channel selection device of the present invention.

[Explanation of symbols]

 1 Microcomputer 2 Low Pass Filter 3 Local Oscillator 4 Mixer 8 Prescaler 9 Memory 10 PLL Circuit 11 Electronic Tuning Tuner

Claims (1)

[Claims] 1. When searching for a broadcasting station, a search operation is performed in which a pulse width modulation signal from a microcomputer is applied to a variable capacitance element of an electronic tuning tuner through a low pass filter, and a tuning obtained by the search operation is performed. As point data, a value obtained by counting the local oscillation frequency of the tuner at that time is stored in a memory, and at the time of tuning, the local oscillation frequency of the tuner is controlled based on the data stored in the memory. apparatus.