JPS6136410B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for counting the number of channels in a television or the like.

Conventionally, automatic tuning devices for televisions and FM tuners equipped with electronic tuning tuners using surface acoustic wave elements (hereinafter abbreviated as SAW elements) have been 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 dividing circuit, 7 is a programmable counter, 8 is a tuning voltage sweep circuit, 9 is a keyboard switch, 10 is an encoder, and 11 is a channel number display device. Here, the SAW element 2 will be explained using FIG. 2. _LiNbO3
An input electrode 1 is placed on a piezoelectric substrate 2 such as or LiTaO ₃ .
The local oscillation output from the electronically tuned tuner 1 is input to the input electrode 12. This is converted from an electric signal to a surface wave at this electrode, and reaches the output electrodes 13 and 14. 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 with each other. Therefore, if we write the signal at the output electrode 13 as V ₁ =Ae ^j 〓 ^t (ω=2πf f: frequency), the signal at the output electrode 14 has a delay time τ
As such, V ₂ = Ae ^j 〓 ^(t- 〓 ⁾ . Since both electrodes are connected to each other,
The composite signal becomes V=V ₁ +V ₂ =Ae ^j 〓 ^t +Ae ^j 〓 ^(t- 〓 ⁾ . The amplitude IVI of this is |V|=A|e ^j 〓 ^t +Ae ^j 〓 ^(t- 〓 ⁾ |=A√2(1+), and this value is ω=2Nπ/τ, that is, f=N/τ(N: integer), the maximum value is 2A ω=(2N+1)π/τ, that is, f=(N+1/
2) Takes the minimum value 0 when /τ (N: integer). The frequency interval Δf that takes the maximum value is as follows: Δf=(N+1)/τ−N/τ=1/τ (τ: constant), which is an equal interval. 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, in the case of domestic use, VHF low band (1 to 3 channels) 150 to 162MHz VHF high band (4 to 12 ch) 230 to 276 MHz UHF band (13 to 62 ch) Select a pass band from a value 4 MHz lower than the first frequency of 530 to 824 MHz, and further set τ = 0.5 μsec, the third frequency in decibel display. The frequency characteristics shown in the figure are obtained. Here, the circled number indicates the peak corresponding to that channel.

Further, FIG. 4 shows a method of constructing the SAW element 2 in the case of three bands. The reason why the two VHF band elements are connected in parallel is because the two bands do not share each other's bands, and in a VHF tuner, its local oscillation output 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 is entered into 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 electrode 12 of SAW element 2, SAW
At the output of the element 2, the level of the local oscillation signal increases or decreases depending on the frequency characteristics of the SAW element 2. Therefore, this output is sent to the detection circuit 3.
By detecting the wave and counting the number of peaks, you can find out how many broadcasting stations it 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 counter 7 counts down these pulses and generates a sweep stop signal when the counter value reaches a predetermined value, for example, 0 for VHF low band, 3 for VHF high band, and 12 for UHF band. When this is applied to the tuning voltage sweep circuit 8 and the sweeping of the tuning voltage is stopped, the tuning is completed. For example, when channel 3 (VHF low band) is selected, the initial value of the counter 7 is 3, but when the local oscillation frequency reaches 162MHz, nine pulses are generated from the waveform shaping circuit 5. As a result, the data in the counter 7 becomes 0 and the channel selection is completed.

Such a channel selection device has the following problems that must be solved.

That is, a coil is often placed at the input of the SAW element 2 for matching with the tuner. Therefore, when receiving the VHF band, the second, third, etc. harmonics of the local oscillation signal are combined between them, pass through the UHF band element, and are detected. Therefore, as shown in FIG. 5, a detected voltage due to harmonics is also obtained by being superimposed on the detected voltage due to the fundamental wave, which is an originally necessary signal. Therefore, there is a high risk that this signal will also be amplified by the amplifier circuit 4 and counted by the counter 7, and as a result, the correct channel may not be received.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and eliminate erroneous counts caused by harmonic interference.

In order to achieve the above object, in the present invention, a switch is provided at the UHF output terminal of the SAW element 2, and when receiving UHF, this switch is closed and the VHF output terminal is closed.
This switch is opened during reception to prevent harmonics from being input to the detector.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 6 shows a first embodiment of the present invention, in which 15 is a UHF band switch terminal, 16 is a resistor, 17 is a diode, 18 is a choke coil, and 19 is a DC blocking capacitor. When the UHF band is received, a DC voltage is applied to the UHF band switch terminal 15. Therefore, the diode 17 becomes conductive and sends the output of the SAW element 2 to the detector 3, thereby performing a tuning operation in the UHF band. On the other hand, when receiving the VHF band, OV is applied to the UHF band switch terminal 15, so the diode 17 becomes non-conductive. Therefore, the harmonics of the local oscillation signal in the VHF band are transmitted to the SAW element 2.
Even if it passes through the UHF band, it will not reach the detector 3. As a result, a detected voltage due to harmonics is not obtained, and only a detected voltage due to the fundamental wave passing through the VHF band portion is obtained, allowing correct tuning operation to be performed.

FIG. 7 is a diagram showing a second embodiment of the present invention. In the same figure, 20 is a UHF matching circuit, 21~
26 is a resistor, 27 and 28 are grounded capacitors, 2
9 is a DC blocking capacitor, 30, 31 is a choke coil, 32, 33 is a transistor, 34 is a
This is a VHF matching circuit. In this embodiment, in order to increase the stability of the tuner, the amount of local oscillation output is reduced and the local oscillation output is amplified by that amount using a high frequency amplifier. Generally speaking, the local oscillation output level is lower in the UHF band than in the VHF band, and the amplifier gain is smaller in the UHF band than in the VHF band. Therefore, in this embodiment, the local oscillation output in the VHF band is amplified by 331 transistors, and the local oscillation output in the UHF band is amplified by 32,332 transistors.

First, during UHF band reception, a DC voltage is applied to the UHF band switch terminal 15, so the transistor 32 operates as an amplifier. For this reason
The output of the SAW element 2 passes through a UHF matching circuit 20, is amplified by a two-stage amplifier circuit consisting of transistors 32 and 33, and is sent to a detector 3. In this way, the UHF channel selection operation is performed.

On the other hand, when receiving VHF band, the UHF band switch terminal 15 becomes OV, so the transistor 32
becomes non-conducting. Therefore, even if harmonics of the VHF band pass through the UHF part of SAW element 2, they cannot reach the detector 3, and the VHF band of SAW element 2 cannot reach the detector 3.
A detected voltage is obtained from only the fundamental wave of the VHF band that has passed through the VHF matching circuit 34 and the transistor 33. Therefore, correct channel selection operation can be performed.

Increasing the local oscillator output in this embodiment means strengthening the electrical coupling between the local oscillator and the SAW. Therefore, in this case, the SAW element also constitutes a part of the local oscillator, and the local oscillator is strongly influenced by the impedance of the SAW element. For example, oscillation frequency shift,
Abnormal oscillation, oscillation skipping (when the voltage applied to the variable cap is changed continuously, the oscillation frequency changes discontinuously from one value to another) and when the +B voltage of the local oscillation circuit is lowered. , stops oscillation even if the amount of descent is small. These phenomena mean unstable operation of the tuner and must be removed.Therefore, the coupling between the local oscillation circuit and the SAW must be made as weak as possible to reduce the local oscillation output.

The present invention can be applied not only to the channel selection device as shown in FIG. 1, but also to a channel number display device as described below. FIG. 8 is a block diagram showing this channel number display device. In the figure, 35 is a channel selection button, 36 is a tuning voltage output circuit,
37 is a tuning voltage reset circuit, and 38 is a channel number display element. When a tuning button 35 is pressed during tuning, a tuning voltage corresponding to that button is generated from a tuning voltage output circuit 36. At the same time, the tuning voltage reset circuit 37 operates to temporarily lower the tuning voltage to OV and then return it to a predetermined value. During this time, the local oscillation frequency of the electronically tuned tuner 1 is swept, so that the local oscillation frequency of the electronically tuned tuner 1 is swept.
A pulse is generated from the frequency dividing circuit 6. The tuning voltage
If the counter 7 is preset to 0 for VHF low band, 3 for high band and 12 for UHF band while the value is decreasing to OV, the counter data will gradually increase from this value. Therefore, for example, when a tuning voltage with a local oscillation frequency of 230 MHz is output, one pulse is generated from the divide-by-3 circuit 6 (see Figure 3), so the data on the counter 7 becomes 4. The channel number display element 38 displays that 4ch is selected.

Even in such a channel number display device, if a detection output due to harmonics occurs, the counter 7 will make an erroneous count, and a channel number greater than the correct channel number will be displayed. Therefore, it is necessary to prevent erroneous counting due to harmonics, and the present invention can be applied to this purpose.

As described above, according to the present invention, harmonics of the VHF band do not reach the detector, so the output signal of the detector is not affected by the harmonics, and the counter does not count incorrectly. do not have. This ensures correct channel counting operation.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing a channel selection device using a SAW element to which the present invention is applied, and Figure 2 is a block diagram showing a channel selection device using a SAW element to which the present invention is applied.
A diagram showing the principle configuration of a SAW element, Figure 3 is a SAW
Characteristic diagram showing the frequency characteristics of the element, Figure 4 is SAW
A diagram showing the practical configuration of the element, FIG. 5 is a signal waveform diagram showing harmonic interference, FIG. 6 is a diagram showing one embodiment of the present invention, and FIG. 7 is a diagram showing another embodiment of the present invention. ,
FIG. 8 is a diagram showing a channel display device using a SAW element to which the present invention is applied. 1: Electronic tuning tuner, 2: SAW element, 3:
Detection circuit, 4: Amplification circuit, 5: Waveform shaping circuit,
6: 3 frequency divider circuit, 7: Counter, 15: UHF band switch terminal, 17: Diode, 32,3
3: Transistor.

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. The detector circuit 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 number, characterized in that a switch element for blocking passage of VHF band harmonics is provided in the UHF output stage of the surface acoustic wave element. 2. The channel number counting device according to claim 1, wherein the switch element is a diode. 3. The channel number counting device according to claim 1, wherein the switch element is a transistor.