JPS6059769B2 - Channel number counting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for counting the number of channels in televisions, etc.

Traditionally, televisions and FM equipped with electronic tuners
Surface acoustic wave devices (hereinafter referred to as S) are used as automatic tuning devices for tuners.
It is abbreviated as AW element.

) is known. FIG. 1 is a diagram showing its configuration, in which 1 is an electronic tuning tuner;
2 is a SAW element, 3 is a detection circuit, 4 is an amplifier circuit, 5 is a waveform shaping circuit, 6 is a frequency divider circuit, 7 is a programmable counter, 8 is a tuning voltage sweep circuit, 9 is a keyboard switch, 10 is an encoder, 11 is a channel number display device. Here, the SAW element 2 will be explained using FIG. 2. An input electrode 12 and an output electrode 13 connected to each other on a piezoelectric substrate 2 such as L1NbO3 or L1TaO3,
14, and the local oscillation output from the electronically tuned tuner 1 is input to the input electrode 12. This is converted from an electrical signal to a surface wave at this electrode, and the output electrodes 13 and 14
reach. Here, the local oscillation signal becomes an electric signal again, but since the output electrodes 13 and 14 are arranged at different distances from the input electrode 12, the signals at both electrodes have a phase difference from each other, and therefore the output When the signal at the electrode 13 is expressed as V, ■Ae"ω" (ω=2Tff: frequency), the signal at the output electrode 14 has a delay time of T.

Since both electrodes are connected to each other, the composite signal is.

The amplitude V of this is, and this value is the maximum value 2Aω=(2N+1)π/τ when ω=2N7r/τ, that is, f=N/τ (N: integer), that is, f=(N
+112)/τ (N: an integer), the minimum value is 0.

The frequency intervals Δf that take the maximum value are equal intervals.

Therefore, the passband of this SAW element 2 is the local oscillation frequency band of each TV broadcast band (VHF low band, VHF high band, UHF band), for example, VF
[F' low band (1~3Ch) 150~162MHz
VHF' high band (4~12Ch) 230~276M
HzUHF band (13-62Ch) 530-824M
If the passband is selected to have a pass band from a value 4 MHz lower than the initial frequency of Hz and further set to τ=0.5 μSec, a frequency characteristic as shown in FIG. 3 in decibels can be obtained.

The circled numbers here indicate the peaks corresponding to that channel. Further, FIG. 4 shows a method of constructing the SAW element 2 in the case of three bands.

■The two positive band elements are connected in parallel so that the two bands do not share each other's bandwidth, and VHF
This is because the local oscillation output of the tuner is output from the same location. Based on the above points, the operation of the channel selection device shown in FIG. 1 will be explained.

When a desired channel number to be selected is input to the keyboard switch 9, the number is converted into a binary code by the encoder 10 and preset in the programmable counter 7.
This is further sent to a channel number display device 11 such as an LED, and the channel number is displayed. When the channel number is input, the tuned voltage sweep circuit 8 starts voltage sweep. When this voltage is applied to the electronic tuner 1, the local oscillation frequency gradually increases. When this output is input to the electrode 12 of the SAW element 2, the level of the local oscillation signal at the output of the SAW element 2 increases according to the frequency characteristics of the SAW element 2. Get bigger or get smaller. Then, by detecting this output with the detection circuit 3 and counting the number of peaks, it is possible to know how many broadcasting stations the signal has passed through and which station it is tuning to. Therefore, this signal is amplified by an amplifier circuit 4, converted into a pulse by a waveform shaping circuit 5, divided by 3 by a frequency divider circuit 6, and sent to a counter 7. The door counter 7 counts down this pulse until the counter value reaches a predetermined value, for example 0 for V8 low band, ■) (3 for F high band).
, Ul+' band, a sweep stop signal is generated when the voltage reaches 12, and this signal is applied to the tuning voltage sweep circuit 8 to stop the tuning voltage sweep, and the tuning is completed. For example, when channel 3 (■HF low band) is selected, the initial value of counter 7 is 3, but the local oscillation frequency is 162.
When the frequency reaches MHz, nine pulses are generated from the waveform shaping circuit 5 (Fig. 3), and the ``result counter 7
The data becomes 0 and the channel selection is completed. Such a channel selection device has the following problems that must be solved.

Local oscillation signal attenuation of SAW element 2 is 20 to 50 dB
Therefore, the local oscillation signal input from the electronic tuner 1 to the detection circuit 3 becomes small. To cope with this, the detection circuit 3 uses a transistor detector that can sufficiently detect and demodulate even small signals. FIG. 5 shows a circuit diagram of a detection circuit using a transistor detector.
20 is a matching circuit, 21 to 25 are bias resistors, 27, 2
8 is a bypass capacitor, 26 and 30 are coupling capacitors, 31 is a detection transistor, and 32 is an impedance conversion transistor.

The local oscillation signal supplied from the SAW element 2 is passed through the matching box 20.
, through the coupling capacitor 26, the detection transistor 31
input to the base of Thereafter, the signal was detected and demodulated by the transistor 31, and the high frequency signal was removed by the capacitor 28. The low frequency demodulated signal is input to the base of the transistor 32 and converted to a low impedance from the emitter.
The signal is input to the amplifier circuit 4 via the coupling capacitor 30. In such a transistor detection circuit, the power supply voltage ■B etc.
When an interference signal in the same frequency band as the low-frequency demodulated signal is superimposed, the transistor 31 also operates as a low-frequency amplifier, so the low-frequency interference signal input to the input of the transistor 31 is amplified, and as shown in FIG. As shown by the solid line A, the normal detection demodulation waveform shown by the dotted line B is disturbed. For this reason, the counter 7 often counted incorrectly, and the correct channel could not be received. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-described drawbacks of the prior art and to provide a channel number counting device that does not cause erroneous counts due to low frequency interference signals such as power supply voltage.

In order to achieve the above object, in the present invention, a filter is provided between the detection circuit and the output terminal of the SAW element to remove signals other than the local oscillation frequency of the electronic tuner, especially low-frequency interference signals, so that regular detection Prevent the demodulated waveform from being disturbed.

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

FIG. 7 is a circuit diagram showing an embodiment of the detection circuit in the channel number counting device of the present invention. Components in FIG. 7 having the same circuit functions as those in FIG. 5 are given the same numbers, and their explanations will be omitted. In the figure, 40 is a coil, and 41 is a capacitor. The value of the capacitor 26 is selected so that it has a low impedance to the local oscillation signal of the electronic tuner and a high impedance to the low frequency interference signal, and forms an element of the high frequency pass filter, and the matching circuit 20 A low frequency interference signal induced in the matching coil or the like is prevented from being input to the detection transistor 31. On the other hand, the value of the capacitor 41 is set so that the impedance is sufficiently low against low frequency interference signals, and the coil 40 is set at a high impedance against the local oscillation signal of the electronic tuner.
It is set to have a low impedance against low frequency interference signals, and constitutes a low frequency signal removal filter. As a result, even if a low frequency interference signal superimposed on the power supply voltage etc. is input to the base of the detection transistor 31, the low frequency interference signal is attenuated by this filter. Not amplified. As a result, the waveform disturbance caused by the low frequency interference signal of the normal detection demodulated waveform is reduced, and correct channel selection is performed. In this embodiment, the detector is constructed of a bipolar transistor, but the same effect can be obtained with a field effect transistor (FET). As described above, according to the present invention, the low-frequency interference signals are attenuated by the time they are input to the detection circuit, so that the output signal of the detection circuit is not affected by these low-frequency interference signals, and the counter does not count erroneously. Never.

As a result, correct channel counting operation is guaranteed and normal channel selection operation can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a channel selection device using a SAW element to which the present invention is applied, Fig. 2 is a pattern diagram showing the principle configuration of the SAW element, and Fig. 3 is a characteristic showing the characteristics of the SAW element. Figure 4 is a pattern diagram showing the practical configuration of a SAW element, Figure 5 is a circuit diagram of a conventional detection circuit in a channel selection device using a SAW element, and Figure 6 shows the output waveform of the detection circuit. The waveform diagram and FIG. 7 are circuit diagrams showing an embodiment of the detection circuit in the channel number counting device of the present invention. 1: Electronic tuning tuner, 2: SAW element, 3: Detection circuit, 4: Amplification circuit, 5: Waveform shaping circuit, 6: 3 frequency division circuit,
7: counter, 20: matching circuit, 31, 32: transistor, 40: coil, 41: capacitor.

Claims (1)

[Scope of Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator, a surface acoustic wave element having a VHF input/output terminal and a UHF input/output terminal into which the oscillation frequency of the local oscillator is input, and a surface acoustic wave element of the element. It includes a detection circuit that detects an output signal, a sweeping means that sweeps the local oscillation frequency, and a counter that counts the number of times the output signal is obtained by the detection circuit. A channel number counting device for determining a channel number, characterized in that a filter is provided between the detection circuit input terminal and the surface acoustic wave element output terminal for suppressing interference signals other than the oscillation frequency of the electronic tuning tuner. Number counting device. 2. The channel number counting device according to claim 1, wherein the filter is a high-frequency band-pass filter that suppresses interference signals at frequencies lower than the oscillation frequency of the electronically tuned tuner. 3. The detection circuit is a detection circuit using a transistor,
Claim 1, characterized in that a low frequency signal removal filter consisting of a series circuit of a capacitor and an inductor is connected between the input terminal of the transistor and the ground, and suppresses a low frequency interference signal at the input terminal of the transistor. Channel number counting device as described.