JPS5911206B2 - Preset channel selection device - Google Patents

Description

[Detailed Description of the Invention] The present invention is applicable to television receivers and video tape recorders (
Regarding preset-type tuning devices such as VTRs, especially tuning devices with an auto-search function that automatically searches for and selects broadcast stations, they can reliably detect tuning with a simple circuit configuration and eliminate noise. The purpose is to prevent search operations from stopping due to spurious signals, and to improve operability and reliability.

With the spread of electronically tuned tuners, preset tuning methods have come to be widely adopted, and various presetting methods have been proposed and implemented. The preset channel selection device with an auto search function to which the present invention relates is excellent in terms of compactness, operability, and serviceability, and is expected to become even more popular in the future.

By the way, in a preset type tuning device equipped with such an auto search function, in order to stop the search (sweeping of the tuning voltage) while tuned to an appropriate receiving station, it is necessary to obtain tuning during the search. It is necessary to reliably detect whether the

In order to detect the tuning state, information such as AFC signal output, video detection output, or the phase relationship between the synchronization signal and the flyback pulse is used, but regardless of which information is used, the tuning state cannot be detected. If you are strict,
For example, a problem arises in that the search does not stop for signals with a weak electric field and presetting cannot be performed.

On the other hand, if the detection of the tuning state is made more lenient, there will be a problem that the search will stop due to very weak electric field signals that would normally not stop the search, such as distant stations that are difficult to hear, or noise. Ru.

Here, a typical example of a conventional preset type channel selection device for a television receiver equipped with an auto search function will be explained with reference to FIG.

To preset the tuning voltage, press search button 1.
Upon pressing , the control circuit 2 begins to continuously send count up command pulses 4 to the counter 3 to sweep the tuning voltage.

The output signal of the counter 3 is sequentially stored in a specific address of the memory 5 designated by the channel selection circuit 6, and at the same time is inputted as an output signal of the memory 5 to the D/A conversion circuit 7 and passed through the low-pass filter (LPF) 8. The voltage is converted into a DC voltage via the DC voltage and supplied to the tuner 9 as a tuning voltage.

The tuner 9 feeds back the AFC signal 10 to the control circuit 2.

When the AFC signal reaches a predetermined value, the control circuit 2 stops the continuous output of the count-up command pulse 4 in order to temporarily stop the search, and then
A count up command pulse 4 or a count down command pulse 11 is controlled to be applied to the counter 3 as necessary so that the C signal maintains a predetermined value.

At this time, in order to detect whether the search is stopped using the correct picture carrier signal, the synchronization separation circuit 1
The synchronization signal 13 from 2 and the flybank pulse 15 from the deflection circuit 14 are respectively applied to a coincidence detection circuit 16 to check whether they match.

If the search is stopped due to the audio carrier signal or noise, a match cannot be obtained between the two, so the control circuit 2 starts the search again by the output signal 1T of the match detection circuit 16. , starts outputting count up command pulse 4 continuously.

As is clear from the above explanation, the detection of the synchronized state is
This is done by checking the match between the C signal, the synchronization signal and the flyback pulse, and in order for the search function to work correctly, the match between the synchronization signal and the flyback pulse must be detected accurately. .

However, if the AFC output appears due to noise or the like and the search is stopped, the synchronization signal obtained by amplitude separation has an irregular pulse waveform.
Frequently, there are accidental coincidences with the erratically oscillating flyback pulses, which stop the search altogether.

Conversely, if the time constant of the coincidence detection circuit is made smaller to make the detection stricter so as to ignore the accidental coincidence of pulses as mentioned above, the signal may deviate from the normal reception state due to slight noise or tuning deviation. There is a risk of it being stored away.

The present invention has been made in view of the problems of the conventional preset type tuning device having auto and search functions as described above. In addition to a simple pulse coincidence detection circuit, it also extracts the degree of pulse coincidence in the form of a pulse phase error signal, which detects whether or not it is in a normal tuning state, making preset operation more efficient and This is what we are trying to do for sure.

An embodiment of the present invention will be described in detail below based on the drawings.

FIG. 2 shows an embodiment in which the present invention is applied as a channel selection device for a VTR.

Since a VTR does not have a deflection system, it is necessary to generate a pulse signal synchronized with a horizontal synchronizing signal, which corresponds to the flybank pulse of a television receiver.

In the example shown in FIG. 2, the PLL circuit 18 is used as a synchronous oscillation circuit, and the synchronization state is checked by detecting a match between the output signal b of the VCO 19 and the synchronization signal a separated by the synchronization separation circuit 12, and the search is stopped. is under control.

At this time, in order to prevent the search from stopping due to noise as described above, the phase error signal C is taken out from the phase comparator circuit 20, and this signal is used to control the gate circuit 21.
is controlled, and if it is not in a normal tuning state, VCO1
The circuit is configured such that the output signal b of No. 9 is gated and turned off so that no coincidence of pulses is observed.

FIG. 3 shows main signal waveforms in the embodiment circuit of FIG. 2.

FIG. 3A shows a signal waveform when tuning is obtained at a regular receiving station.

Since the synchronization signal a and the output signal b of the VCO 19 are almost completely synchronized, the phase error signal C has a very short downward pulse waveform, as shown in figure a, or is always at a high level. is maintained.

Therefore, the signal waveform d obtained through the integrating circuit 22 is as shown in Figure A, and the signal waveform-shaped by the comparator 23 always maintains a high level.

Therefore, the output signal b of the VCO 19 is always output to the gate circuit 21.
is applied to the coincidence detection circuit 16, a coincidence with the synchronization signal a is detected, and the search is stopped.

On the other hand, FIG. 3A shows an example of each signal waveform when the search is stopped due to noise.

Since the input of the synchronization separation circuit 12 is noise, the synchronization signal has an irregular pulse waveform as shown in a of FIG. 3A.

Therefore, the PL affected by this irregular synchronization signal
The output signal b of the L circuit 18 also has an irregular pulse waveform, or continues to oscillate near the free-run frequency, and in any case, phase synchronization with the synchronization signal a cannot be obtained.

However, there are often moments when the output polarity (high level or low level) coincides between waveforms a and b, and if you pass them through a simple pulse coincidence detection circuit, it will not be possible to detect that the pulses have coincided. There is a risk that it may be considered.

Therefore, in order to detect the state of tuning more accurately, the phase error signal C of the phase comparator circuit 200 is used.

When two mutually irregular pulse waveforms as shown in a and b in FIG. 3A are input to the phase comparator circuit, the phase error signal has a waveform as shown in, for example, C in the same figure.

Therefore, the integrated waveform obtained through the integrating circuit 22 is as shown in d, and when this waveform is shaped by the comparator 23, the gate signal e is obtained.

The gate circuit 21 takes M of the two input signals b and e and passes the output b of the PLL circuit 18 only at the moment when the output signal e of the comparator 23 is at a high level, so the output of the gate circuit 21 is , the waveform becomes as shown in FIG.

The worse the synchronization between the two input signals a and b, the longer the phase error signal C stays at a low level. Therefore, the value of the integral value d becomes smaller, and the output b of the PLL circuit is reduced by the gate circuit 21. The rate of being gated off also increases.

Therefore, the worse the synchronization between the synchronization signal a and the output signal b of the PLL circuit, the lower the probability that pulse coincidence will be detected, and it is possible to prevent the search from stopping due to malfunction.

Furthermore, the output b of the PLL circuit 18 is controlled by the gate circuit 21.
The probability that the gate will be gated off also depends on the threshold voltage of the comparator 23, so by operating the variable resistor 24 that sets the threshold voltage and setting the threshold voltage appropriately, the automatic It is also possible to appropriately set the lower limit of the input signal electric field strength required to stop the search.

In the case of the embodiment shown in FIG. 2, the lower the threshold voltage is, the lower the probability that the output b of the PLL circuit will be gated off by the gate circuit 21, and even a signal with a fairly weak electric field can be searched. will stop.

As is clear from the above embodiments, in addition to the conventional pulse coincidence detection circuit, the present invention extracts a pulse phase error signal and provides a gate-sle circuit using this signal, thereby detecting the search caused by malfunctions caused by noise, etc. To provide an excellent preset type tuning device which solves poor operability and reliability, such as so-called search errors, such as stopping of the radio, not selecting a necessary station, or conversely stopping at a station that is too weak, with a simple circuit configuration. It is something.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional preset type tuning device, FIG. 2 is a block diagram showing an example of a preset type tuning device according to the present invention, and FIG. 3 is an example of the embodiment of FIG. 2. FIG. 2...Control circuit, meter...Counter, 5...
...Memory, 6...Tuition selection circuit, 7...
...D/A conversion circuit, 9...-tuner, 12
...One synchronization separation circuit, 16...Pulse coincidence detection circuit, 18...PLL circuit, 19...
...vCO, 20...phase comparison circuit, 21.
...-gate circuit, 22...integrator circuit, 2
3-... Comparator, 24... Variable resistor.

Claims (1)

[Claims] 1. A control circuit that outputs a control signal for raising and lowering a counter for tuning sweep, a memory circuit that sequentially stores the output of the counter at a specific address specified by a tuning circuit, and a D/A converter that converts it into an analog value and applies it to the tuner as a tuning voltage; a synchronous oscillator whose phase is controlled by a reference signal obtained from a signal received by the tuner via a synchronous separation circuit; a circuit that detects a phase error between an oscillation output of an oscillation device and the reference signal, gates the oscillation output via an integrating circuit, and detects coincidence between the oscillation output output from the gate circuit and the reference signal; and a match detection circuit,
The output of the coincidence detection circuit and the AFC from the tuner
A preset type tuning device characterized in that an output is inputted to the control circuit.