JPS601970B2 - channel count circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel number counting circuit in a television surface acoustic wave channel selection device.

The example shown in FIG. 1 is known as a channel selection device using a surface acoustic wave device (hereinafter abbreviated as a SAW device).

In the figure, 1 is an electronic tuning tuner having a voltage-controlled local oscillator, and 2 is an input electrode 9, as shown in FIG.
3 is a SAW element having two output electrodes 10 and 11 connected to each other and forming a comb-shaped filter.
Detection/amplification circuit for detecting the output of element 2 and amplifying it to a desired level; 4 is a waveform shaping circuit for converting the output of detection/amplification circuit 3 into pulses; 5 is the channel number to be selected. keyboard switch for entering,
6 is an encoder for binarizing the channel number input from the keyboard switch; 7 is a counter to which the output of the encoder 6 is preset and counts down the pulses sent from the waveform shaping circuit 4 with that value as the initial value; Reference numeral 8 denotes a tuned voltage sweep circuit in which voltage sweep is started when a channel number is input to a keyboard switch, and voltage sweep is stopped by a count end signal generated by counter 7. The operation of the main channel selection device will be described below.

When a desired channel number to be selected is input to the keyboard switch 5, it is converted into a binary number by the encoder 6 and preset in the counter 7. On the other hand, when the channel number is input, the tuning voltage pulling circuit 8 starts voltage pulling, and as a result, the local oscillation frequency of the electronic tuning tuner 1 gradually increases from a certain frequency. This local oscillation output is input to the SAW element 2. The SAW element 2 has a structure as shown in FIG.
and reaches 11. The surface wave is converted into an electric signal again at the electrode, but since the signal converted at electrode 11 has a longer propagation distance than the signal converted at electrode 10,
It has a delay time of 2 compared to the signal converted by 0.
Therefore, if the signal voltage converted at the electrode 10 is expressed as Aej t (=2, where f is the frequency), the signal voltage at the electrode 11 is multiplied by Aej (t-r). Since both poles are connected to each other, the output voltage at the output terminal of the SAW element 2 is V2A {ej's t0 ej's (t-?)}...[1}, and the output voltage is applied to the detection and amplification circuit 8. When the amplitude is detected and amplified, the output voltage is V, with the voltage gain being G.

Ni GIAI Ni GA'no 2 (10 COS pieces),. 、．・
・'2).

Therefore V. is the frequency f is fN/ke where N is an integer...
The maximum value is reached at {31, and the frequency interval is 1/7.

In the case of television, in many cases the local oscillation frequencies of broadcasting stations exist at equal intervals, so if you sweep the local oscillation frequency and count the peak points of the output of the detection/amplification circuit 3, you can determine how many broadcasting stations have passed. I can see what you did. Therefore, this world power is converted into pulses by the waveform shaping circuit 4 and sent to the counter 7. The counter 7 counts down the output pulses of the waveform shaping circuit 4 using the channel number input from the keyboard 5 as an initial value, and generates a count end signal when the count ends. This signal is applied to the tuning voltage sweep circuit 8 as a sweep stop signal. As a result, the voltage sweep of the tuning voltage reduction circuit 8 is stopped and maintained, and therefore the local oscillation frequency of the electronic tuning tuner 1 is maintained at a desired value, and tuning is completed. How to select a comb-shaped frequency interval when the surface acoustic wave tuning device as described above is applied domestically will be explained using the table below. TABLE 1 VHF LOW BAND' For now, a comb filter of MH2 equal to the channel spacing can be used.

In this case, the integer N is 150/
6=25, 26 and 27 for the 2nd and 8th channels respectively
It is. Alternatively, the output pulse of the waveform shaping circuit 4 may be frequency-divided by three using a 2MH2 comb filter. in this case,
The integer N is 7 for each of the first, second, and third channels.
5, 78, 81. Also, when it comes to UHF van days,
The output of the waveform shaping circuit 4 may be frequency-divided by eight using a 2MH2 comb filter. In this case, the integer N is 2 for each of the 13th, 14th..., 62nd channels.
65 2 eel, 412. However,
In the VHF high band, the peak MH2 is between the 7th and 8th channels, and the others are aMH2, so the above method cannot be uniformly adopted. Therefore, a special SAW element is provided, or the VHF/. It was necessary to use other channel selection methods only for those bands. SUMMARY OF THE INVENTION An object of the present invention is to provide a channel counting circuit for a surface acoustic wave tuning device which eliminates the drawbacks of the prior art described above and is capable of receiving not only the VHF low band and UHF band but also the VHF/-band.

In order to achieve the above-mentioned object, in the present invention, when the frequency intervals of the channels are not the same, for example, VHF/.
In the diband, the frequency interval of the comb filter is selected as a common divisor of mother MH2 and Komachi Z, and a pulse generation circuit is provided that generates a specific number of pulses when the number of outputs of the detector reaches a specific value. The number of channels is determined based on the sum of the output of the pulse generation circuit and the number of outputs of the detector.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a diagram showing an embodiment of the present invention, and the same parts in FIG. 4 as in FIG. 1 are designated by the same numbers.
In FIG. 4, 12 is a pulse generation circuit that generates one pulse when the number of pulses sent from the waveform shaping circuit 4 reaches 12, and 13 is a pulse generation circuit that generates one pulse when the number of pulses sent from the waveform shaping circuit 4 reaches 12. An OR circuit 14 takes the OR circuit 14 and the output pulse of the OR circuit 13.
This is a divide-by-3 circuit that divides the frequency. Next, the operation of this channel count circuit will be explained.

In this case, the delay time 7 of the SAW element 2 is selected to be 1/2 microsecond so that the output becomes maximum every two days as shown in FIG. In this case, the integer N corresponding to the fourth channel is 230/2=115. For this reason,
As shown in FIG. 6, from the waveform shaping circuit 4, the local oscillation frequency of the electronic tuning tuner 1 is changed every 2 MHz.
pulses are generated. The pulse generating circuit 12 generates one pulse when the number of pulses sent from the waveform shaping circuit 4 reaches 12. This is shown by A in FIG.
The OR circuit 13 ORs the pulse sent from the waveform shaping circuit 4 and the combined pulse sent from the pulse generation circuit 12, and the frequency is divided by three in the frequency divider circuit 14.

Therefore, the output pulses of the frequency divider circuit 14 are as shown in FIG. 7, and pulses corresponding to each channel are extracted. By sending this pulse to the counter 7, the surface acoustic wave tuning device described above can also be applied to the VHF high band. In this embodiment, the delay time 7 of the SAW element 2 is selected to be 1/2 microsecond so that a pulse is generated every 2 MH2, but the present invention is not limited to this value.

For example, if the delay time is selected to be 1 microsecond and a pulse is generated every IMH2, a circuit that generates two pulses is installed after the pulse corresponding to the 7th channel, and then the frequency is divided by 6. do it. Also, the above explanation is
Although the case of domestic channels has been described, the present invention can also be applied to the same aircraft in the case of foreign channels.

As described above, according to the present invention, it is possible to apply the above-described surface acoustic wave tuning device even to bands in which broadcast stations exist in which frequency intervals are not uniform.

Therefore, there is no need to adopt a different channel selection method only for bands whose frequency intervals are not uniform or to provide a special surface acoustic wave element.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a surface acoustic wave tuning device to which the present invention is applied, Fig. 2 is a configuration diagram of a SAW element, Fig. 3 is a characteristic diagram of the device shown in Fig. 1, and Fig. 4 is a diagram of the present invention. Block diagrams showing embodiments of the channel counting circuit according to the invention, FIGS.
FIG. 7 is a characteristic diagram illustrating the operation of the circuit shown in FIG. 4. 1...Electronic tuning tuner, 2...SAW element, 3.
...Detection amplifier circuit, 4...Waveform shaping circuit, 5
...Keyboard switch, 6...Encoder, 7...
... Counter, 8... Tuned voltage sweep circuit, 9,
10,1 1... Electrode, 12... Pulse generation circuit, 13... OR circuit, 14...
3 frequency divider circuit. O, 2, 3, O, 4, S, 5, 7

Claims (1)

[Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator, a tuned voltage sweep circuit for sweeping the oscillation frequency of the local oscillator, a comb-shaped filter using a surface acoustic wave element that inputs the output of the local oscillator, and In a surface acoustic wave tuning device that includes a detector that detects the reliability signal of a filter and selects a channel using the output of the detector, when the number of outputs of the detector reaches a specific value, a specific signal is detected. The method is characterized by comprising a pulse generating circuit that generates pulses as many as the number of pulses, and means for calculating the sum of the output of the pulse generating circuit and the number of outputs of the detector, and determining the number of channels based on the output of the means. Channel count circuit.