JPS6059768B2 - Channel number counting device - Google Patents

Description

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

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. LiNbO. An input electrode 12 and an output electrode 13 connected to each other on a piezoelectric substrate 2 such as or LiTaO3,
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 1, 3, 1
Reach 4. 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 filtered, the signal at the output electrode 14 has a delay time τ
As.

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

The amplitude 1VI of this is, and this value is the maximum value 2Aω=(2N+1)π/τ when ω=2N7r/γ, that is, f=N/τ (N: integer), that is, f=(N
+112)/τ (N: 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 broadcasting band (HF low band, VHF high band, UHF band), for example, in Japan, low pant (1 to 3 channels) 150 to 162 MHz. High band (4-12ch) 230-276MHzUH
F band (13-62Ch) 530-824MH
If the passband is selected to start from a frequency lower than the first frequency of z, and further set to, for example, τ=0.5 μSec, the passband is shown in decibels as shown in Figure 3 (in Figure 3, the passband starts from a frequency 4 MHz lower).

) The frequency characteristics shown in () can be 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 band elements are connected in parallel is that the bands do not share each other's bandwidth, and ■
This is because in a normal 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 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 further includes 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. This output is sent to SAW element 2
When input to the electrode 12 of the SAW element 2, the SAW
Depending on the frequency characteristics of the element 2, the level of the local oscillation signal increases or decreases. Therefore, 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 is amplified by an amplifier circuit 4, converted into a pulse by a waveform shaping circuit 5, and then converted into a pulse by a frequency divider circuit 6.
The frequency is divided by 3 and sent to counter 7. The counter 7 counts down this pulse, and sweeps when the value of the counter reaches a predetermined value, for example, 0 for the - band, 3 for the VHF high band, and 12 for the positive band. When a stop signal is generated and applied to the tuning voltage sweep circuit 8 to stop sweeping the tuning voltage, tuning is completed. For example, when channel 3 (VHF 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 as a result, the data in the counter 7 becomes 0, completing the channel selection. 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 a tuner. Therefore, when receiving the HF band, the third, 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 50 due to harmonics is also obtained by being superimposed on the detected voltage 50 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. Furthermore, since each terminal of the SAW element is connected to the output terminal of the SAW element sealing container with a wire bond inside the container, sufficient signal separation between the positive output terminal and the UHF output terminal cannot be obtained.

In addition, due to coupling between the matching coils of each band or the output terminals of the SAW elements, at the UHF bad frequency, in addition to the normal UF [F band signal], unnecessary wave components with different phases and levels are input to the detector. However, the waveform is not normal. For this reason, as shown by the solid line in Figure 6, an extra waveform appears or a waveform is missing compared to the detected voltage waveform (dotted line) that should be obtained, leading to incorrect counting, and as a result, the correct channel There were cases where I was unable to receive the message.
The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to provide a channel number counting device that can prevent harmonics caused by these combinations and comb-shaped disturbances in the multiplication band, and can prevent erroneous counting of the counter. It is about providing.

In order to achieve the above object, the present invention provides VHF. (5UHF output terminal or
A switch is provided in the matching circuit of +', and this switch is connected to VHFI:N. By switching from UHF to VF[F
Blocks UHF band signals during reception, and switches to S during normal reception.
UHF from AW's ■HF terminal or ■HF matching circuit
Prevents erroneous counting by blocking unnecessary wave signals and preventing them from being input to the detector.

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

FIG. 7 is a circuit diagram showing the first embodiment of the present invention,
This is a circuit diagram showing a circuit for preventing erroneous counting.
In the figure, 15 is a UHF band switch terminal, 42 is an f band switch terminal, 16, 18, and 41 are resistors,
16 and 40 are diodes. When the UFIF band is received, a DC voltage is applied to the armband 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. At this time, the resistor 18 causes a current voltage drop due to the tie current, and the HF terminal 42 becomes O■, so
Diode 40 becomes non-conductive. Therefore, even if a UHF band signal leaks from the output end of the SAW element 2, these unnecessary wave component signals having different phases and levels are blocked and will not reach the detector 3. As a result, at the f-band frequency, there is no disturbance of the comb-shaped waveform, and correct channel selection can be performed. On the other hand, when receiving the band (2), a DC voltage is applied to the (2) HF band switch terminal 42, so the diode 40 becomes conductive and the signal of the (2) band is transmitted to the detector 3. At this time, since O■ is applied to the UHF band switch terminal 15, the diode 17
becomes non-conducting. Therefore, even if the harmonics of the local oscillation signal in the positive band pass through the U8 band portion of the SAW element 2, they will not reach the detector 3. As a result, a detected voltage due to harmonics is not obtained, but only a detected voltage due to the fundamental wave that has passed through the VHF band portion is obtained, allowing correct tuning operation to be performed. FIG. 8 is a diagram showing a second embodiment of the present invention.

In the same figure, 20 is a UHF matching circuit, 21 to 26, 44
is a resistor, 27 and 28 are grounded capacitors, 29 is a DC blocking capacitor, 30 and 31 are choke coils, 32 and 3
3 is a transistor, 34 is a VHF matching circuit, 45 is a DC blocking capacitor, 45 is a coil, and 46 is a diode. 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 level of the local oscillation output is lower in the f band than in the positive band, and the gain of the amplifier is lower than in the positive band.
F band is smaller. Therefore, in this embodiment, the local oscillation output in the VHF band is amplified by 331 transistors,
The U8 band local oscillation output is provided by transistors 32 and 332.
The stones are amplified. First, when receiving the UHF band,
Since a DC voltage is applied to the HF band switch terminal 15, the transistor 32 operates as an amplifier.

Therefore, the output of the SAW element 2 is sent via a UHF matching circuit 20 to a detector 3 where it is amplified by a two-stage amplifier circuit including transistors 32 and 33. At this time, a DC voltage is applied to the VHF band switch terminal 42, and the diode 46 becomes conductive. Therefore, unnecessary wave components that disturb the comb-shaped waveform due to internal coupling of the SAW element 2 and coupling between circuit components such as the HF matching circuit 34 and the UHF amplifying transistor 30 fall to the ground potential and are blocked, and the detector 3
A normal or square waveform is transmitted to the terminal, and normal tuning operation can be performed. The coil 45 operates as a choke coil when receiving the U8 band or as a matching coil when receiving the f band, and does not attenuate the Ul+' signal. In this way, the channel selection operation for f is performed. On the other hand■
■When receiving HF band, the armband switch terminal 42 is O.
■The HF signal is not attenuated, and the signal is amplified by the transistor 32, and the detector 3
transmitted to. At this time, the coil 45 is V)IF'
It becomes part of the matching circuit and does not attenuate any positive signals. Further, since the UHF' band switch terminal 15 becomes O■, the transistor 32 becomes non-conductive. Therefore, even if the harmonics of the V8 band pass through the UHF section of the SAW element 2, they can still reach the detector 3. Detection voltage based only on the fundamental wave of the HF band can be obtained. 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, from the perspective of the local oscillator, 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 drift, abnormal oscillation, oscillation skip (when the voltage applied to the varicap is changed continuously, the oscillation frequency changes discontinuously from a certain value to a certain value), and local oscillation circuit +
If the B voltage is lowered, oscillation will be stopped even if the amount of drop is small. These phenomena mean unstable operation of the tuner and need to be removed.Therefore, it is necessary to weaken the coupling between the local oscillation circuit and the SAW as much as possible and reduce the local oscillation output. The present invention can be applied not only to a channel selection device as shown in FIG. 1, but also to a channel number display device as described below.

FIG. 9 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 the tuning button 35 is pressed during tuning, the tuning voltage corresponding to that button is output to the tuning voltage output circuit 36.
arises from. At the same time, the tuning voltage reset circuit 37 operates to temporarily lower the tuning voltage to 0V, and then restore it to a predetermined value. During this time, the local oscillation frequency of the electronically tuned tuner 1 is swept, so that pulses are generated from the divide-by-3 circuit 6 in exactly the same way as in the channel selection device of FIG. While the tuning voltage is dropping to 0V, preset counter 7 to 3 for VHF low band, 3 for O high band, and 12 for UYIF band, and the counter data will gradually increase from this value. do. Therefore, for example, when a tuning voltage that makes the local oscillation frequency 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 occurs due to harmonics or disturbances in the comb-shaped waveform of the UHF band, the counter 7 will miscount and display a channel number higher or lower than the correct channel number. . Therefore, it is necessary to prevent erroneous counting due to harmonics or disturbances in the comb-shaped waveform of the UFIF, and the present invention can be applied to this purpose. As described above, according to the present invention, the harmonics of the VF [F band] never reach the detector, so the influence of the harmonics does not appear on the output signal of the detector, and the UHF band reception Since there is no disturbance in the comb-shaped waveform at the time, the counter will not count incorrectly.

As a result, correct channel counting operation is guaranteed.

[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 shows the frequency characteristics of the SAW element. Characteristic diagram, Figure 4 is a pattern diagram showing the practical configuration of the SAW element, Figure 5 is a waveform diagram showing harmonic interference,
FIG. 6 is a waveform diagram showing the disturbance of the comb-shaped waveform due to unnecessary wave components during UHF band reception, FIG. 7 is a circuit diagram showing an embodiment of the erroneous count prevention circuit in the present invention, and FIG. FIG. 9 is a circuit diagram showing another embodiment of the count prevention circuit, and is a block diagram of a channel number display device to which the erroneous count prevention circuit of the present invention can be applied. 1...Electronic tuning tuner, 2...SA
W element, 3...detection circuit, 4...amplifier circuit, 5...waveform shaping circuit, 6...
Frequency dividing circuit, 7...Counter, 15...UHF
Band switch terminal, 17, 40, 46... Diode, 42...■ Positive band switch terminal, 3
2,33...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. 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. In the channel number counting device for determining the number, a first switch element for blocking the passage of harmonics of the VHF band is provided at the UHF output stage of the surface acoustic wave element, and a first switch element for blocking the passage of harmonics of the VHF band is provided at the output stage of the VHF band. A channel number counting device characterized in that a second switch element is provided for blocking passage of unnecessary wave components having different phases and levels. 2. The channel number counting device according to claim 1, wherein the first and second switching elements are diodes. 3. The channel number counting device according to claim 1, wherein the first switching element among the band switching elements is a transistor, and the second switching element is a diode.