JPS6058607B2 - 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.

Conventionally, surface acoustic wave devices (hereinafter referred to as SA) have been used as automatic tuning devices for television FM tuners equipped with electronic tuning tuners.
It is abbreviated as W 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. LiNb0. and LiTaO. An input electrode 12 and an output electrode 13 connected to each other on a piezoelectric substrate 2, such as
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, 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 with each other. Therefore, when the signal at the output electrode 13 is filtered, the signal at the output electrode 14 becomes a signal with a delay time τ.

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

The amplitude of this is 1V1, and this value is ω=2N? When r/τ, that is, f=N/τ (N: integer), the maximum value ω=(2N+1)π/τ, that is, f=(N+
↓)/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 (VHF low band, VHF high band, UHF band), for example, in the case of domestic
Low band (1~3ch) 150~162MHz ■ Positive high band (4~12ch) 230~276MHz UHF
Band (13-62Ch) 530-824MHZ
If we choose to have a passband from a value 4M ratio lower than the first frequency of , and further set τ = 0.5μSec, we get
A frequency characteristic as shown in FIG. 3 can be obtained in decibels.

Here, the circled number indicates the peak corresponding to that channel. In addition, SAW element 2 in the case of 3 bands
Fig. 4 shows the construction method. ■The reason why the two f-band elements are connected in parallel is that the two bands do not share each other's bandwidth, and ■The local oscillation output of the arm 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 increases or decreases in accordance with the frequency characteristics of the SAW element 2 at the output of the SAW element 2. 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 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 this pulse until the counter value reaches a predetermined value, for example V.
■0 for J-band, . 3 for VHF high band,
When the Uf band reaches 12, a sweep stop signal is generated, and when this signal is applied to the tuning voltage sweep circuit 8 to stop the tuning voltage sweep, tuning is completed. for example,
When channel 3 (VHF band) is selected, the initial value of the counter 7 is 3, but when the local oscillation frequency reaches 162 MHZ, nine pulses are generated from the waveform shaping circuit 5 (Figure 3). , as a result, the data of counter 7 is O
Then, the selection is completed. Such a channel selection device has the following problems that must be solved. The first point is that when receiving HF low band, the second high frequency of the local oscillation signal passes through the high band element.
The signal is input to the detection amplifier circuit 4 and detected. Since the tuning operation starts by sweeping the tuning voltage from 0V, the local oscillation frequency starts sweeping from about 120 to 130 MHz. The frequency of 240 to 276 MHz of this double harmonic overlaps with the frequency of the positive high band. For this reason, as shown in Figure 5, the output waveform of the detection amplifier circuit appears as a waveform due to the second harmonic superimposed on the waveform that should be counted normally, which disturbs the normal waveform and causes the counter 7 to often count incorrectly. However, it has the disadvantage of not being able to receive the correct channel. The second point is that since each terminal of the SAW element is connected with a wire inside the container to the input/output terminal of the SAW element sealing container, VH
Sufficient signal separation between the F output terminal and the UHF output terminal cannot be obtained. In addition, coupling occurs between the SAW elements of each band and the tuner or the matching coil of the high frequency amplifier circuit. These couplings are particularly strong in the high frequencies of the UHF band, so in the high frequencies of the UHF band, in addition to the normal signal, unnecessary wave components with different phases and levels are input to the detection amplifier circuit. As shown by the solid line in Figure 6, the waveform that should be counted normally (shown by the dotted line)
Compared to this, the waveform is distorted, and therefore, in this case as well, the counter 7 often counts incorrectly and the correct channel cannot 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 prevents erroneous counts caused by waveform disturbances caused by these couplings and harmonics.

In order to achieve the above object, in the present invention, S
A filter including a switch element is provided in the circuit between the VHF output terminal of the AW element and the detector, and by switching the switch element, harmonics of the VHF low band and unnecessary wave components of the U8 band are prevented from being input to the detector. , to prevent erroneous counting.

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 present invention, in which 20 is an f matching circuit, 21 to 27 are resistors, and 28
, 30 are bypass capacitors, 29, 31, and 35 are DC blocking coupling capacitors, 36, 37 are filter capacitors, 38, 39 are choke coils, 45, 46 are transistors, 41 is a high frequency switching diode, 42 is a DC switching diode, 43 is an HF low band voltage terminal, 44 is a group F band voltage terminal, 40 surrounded by a dotted line is a VHF matching circuit, 50 is a filter circuit, 32 is a matching coil, and 33 and 34 are filter coils. 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, the local oscillation output is smaller in the UHF band than in the VHF band, and the amplifier gain is smaller in the group f band than in the f band. Therefore, in this embodiment, the local oscillation output in the V8 band is amplified by one transistor 46, and the local oscillation output in the UHF band is amplified by 45,462 transistors. When receiving UHF band, UHF band voltage terminal 4
Since a DC voltage is applied to transistor 5, transistor 45 operates as an amplifier. Therefore, the output of SAW element 2 is group f
The signal passes through a matching circuit, is amplified by a two-stage amplifier circuit including transistors 45 and 46, and is sent to the detector 3. At this time,
The high frequency switching diode 41 becomes conductive because a DC voltage is applied through the DC switching diode 42 and the resistor 27. Since the capacitor 36 is selected to be a number + PF, it has a low impedance at high frequencies in the UHF band. (For example, with 40PF, frequency 90
(The impedance of the capacitor at ct11Hz is approximately 4Ω) This eliminates the need to disturb the comb-shaped waveform due to internal coupling of the SAW element 2, coupling between circuit components of the VHF matching circuit 32 and the positive matching circuit 20, or the UHF amplification transistor 45. The wave component falls to the ground potential and is attenuated, and a normal comb-shaped waveform is transmitted to the wave detector 3, allowing normal tuning operation. At this time, the HF filter circuit uses a choke coil or the first stage transistor 45 and the second stage transistor 4 when receiving the UHF band.
6 matching coil and does not attenuate the UHF signal. On the other hand, when the positive band is received, the Uf band voltage terminal 44 becomes O■, so the transistor 45 becomes non-conductive. Therefore, in the VHF band, the VHF output signal of the SAW element 2 passes through the matching circuit 40 and the filter circuit 50, is amplified by the transistor 46, and reaches the detector 3. First, during HF low band tuning, a DC voltage is applied to the VHF low band voltage terminal 43, so the high frequency switching diode 41 becomes conductive, and a capacitance of several tens of PF of the capacitor 36 is added between the signal line and the ground. In the positive low band, the impedance is high;
It becomes one element of the filter, and the cutoff frequency of the filter is low, matching the pass frequency band of the VHF high band.
Attenuates the second harmonic of the HF low band. As a result, when the SAW element 2 selects a VHF low band, a detected voltage based only on the fundamental wave can be obtained. When selecting VHF high band, VHF low band voltage terminal 43 becomes O■,
The high frequency switching diode 41 becomes non-conductive, the cutoff frequency of the filter circuit becomes high, and the VHF high band signal from the SAW element 2 is amplified by the transistor 46.
, is transmitted to the detector 3. In the manner described above, normal channel selection operation can be performed. As mentioned above, V
It can attenuate the harmonics of the HF low band and also attenuate unnecessary wave components due to coupling when selecting the U positive band, so these effects will not appear on the output signal of the detector, so the counter will not count incorrectly. There isn't.

This ensures correct channel counting operation. In addition, the present invention provides V by just switching one element.
It is possible to prevent erroneous counting when selecting channels in the HF low band and UHF band, and has the advantage of less cost increase.

[Brief explanation of drawings]

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. Figure 4 is a pattern diagram showing the practical configuration of the SAW element, Figures 5 and 6 are waveform diagrams showing the output characteristics of the detection amplifier circuit, and Figure 7 is a pattern diagram showing the actual configuration of the SAW element. FIG. 2 is a circuit diagram showing an example of an erroneous count prevention circuit. 1: Electronic tuning tuner, 2: SAW element, 3: Detection circuit, 4: Amplification circuit, 5: Waveform shaping circuit, 6: Frequency dividing circuit, 7
: Counter, 41: High frequency switching diode, 4
3: VHFa-band voltage terminal, 44: UHF band voltage terminal, 36: capacitor, 50: filter.

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 an output of the element. The detector circuit includes a detection circuit that detects a 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 the number includes at least a filter circuit between the VHF output terminal of the surface acoustic wave element and the detection circuit, and when the VHF low band
A channel number counting device characterized by being provided with a switch element for blocking F low band harmonic signals and attenuating unnecessary wave components having different phases and levels when selecting a UHF band. 2. The switching element is configured by connecting a diode and a capacitor in series, and the diode is placed in a conductive state when selecting a VHF low band and a UHF band, and is set in a blocked state when selecting a VHF high band, so that the pass frequency band of the filter is When the diode is conductive, the frequency band is the VHF low band, and the blocking frequency band is the VHF high band and UHF band, and when the diode is in the blocking state, the passing frequency band is the VHF high band. A channel number counting device according to claim 1, characterized in that: