JPS601971B2 - Surface acoustic wave tuning device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic tuning device using surface acoustic wave elements in television receivers, FM tuners, and the like.

In television receivers, so-called electronic tuning tuners, which use electronic variable elements such as varicaps in the tuning circuit, have come to be used, and with this, automatic selection using keyboard switches, touch switches, etc. Tubes that can be used for broadcasting have come into practical use. An example of such a tuner selection device is one having a configuration as shown in FIG. 1, for example.

This tuning device uses a surface acoustic wave element, and 1 is an electronic tuning tuner having a voltage-controlled local oscillator;
Surface acoustic wave elements (hereinafter referred to as SA) that constitute the comb-shaped filter
(W element is abbreviated), 3 is a detection/amplification circuit that detects the output of the SAW element 2 and amplifies it to an unnecessary level, 4
is a waveform shaping circuit that converts the output of the detection/amplification circuit 3 into pulses; 5 is a keyboard switch for inputting a desired channel number to be selected; and 6 is a binary encoder for the channel number input to the keyboard switch 5. The encoder 7 is preset with the output of the encoder 6, and the counter 8 counts down the pulses sent from the waveform shaping circuit 4 with that value as the initial value.When the channel number is input to the keyboard switch 5, the voltage sweep operation starts. This is a tuned voltage reduction circuit which stops the voltage sweep operation in response to a termination signal applied from the counter 7.

Next, the operation of this device will be explained.

When the channel number of a broadcasting station to be selected is input to the keyboard switch 5, the encoder 6 encodes the channel number in binary and presets the value in the counter 7.

At the same time, a start signal is applied from the keyboard switch 5, and the tuned voltage bridge circuit 8 starts the voltage bridge operation, whereby the oscillation frequency of the local oscillator of the tuner 1 gradually increases from a certain frequency.

The oscillation output from this local oscillator is supplied to the SAW element 2. As shown in FIG. 2, this SAW element 2 is made of crystal,
An input electrode 9 and two sets of output electrodes 10 connected to each other are formed on a suitable substrate exhibiting dew strain characteristics such as barium titanate porcelain.
, 11, when the local output of the tuner is supplied to the input electrode 9, it is converted into a surface acoustic wave and propagated on the substrate, and when it reaches the output electrodes 10 and 11, it is converted back into an electrical signal. However, at this time, since the distance from input electrode 9 to output electrode 10 and the distance to output electrode 11 are different, there is a distance difference between the signals appearing at electrodes 10 and 11. Accordingly, a delay time 7 is generated. Therefore, the voltage that is now converted into an electrical signal by the electrode 10 and appears as an output is V. o, and this is expressed as follows: V,.

=Aej■tHowever, =2　f, f=frequency The voltages V, . teeth VII=Aej■ (at t-) It can be expressed as

Since these electrodes 10 and 11 are connected in parallel, the voltage V at the output of the SAW element 2 is V-VI.

10VII Ni A {ej's t+ej■ (t-?)},
When this voltage V is detected and amplified by the detection/amplification circuit 3, the output voltage Vo becomes V.

NiG.・VI Ni G, A no 2 (10 COS no D) However, G
: The amplification degree of the detection/amplification circuit 3.

Therefore, the output voltage Vo obtained through the detection/amplification circuit 3 becomes maximum when the frequency f of the local oscillator output is f = where N: an integer, and the interval △f between the frequencies showing the maximum value.
becomes 1/T.

That is, in the SAW element 2, by selecting this delay time to a predetermined value, a comb-shaped filter with a desired frequency interval can be constructed.

In addition, the SAW element 2 has the electrode spacing shown in FIG.
When the velocity of the surface acoustic wave on the substrate is set as
This shows the bandpass characteristic of the center frequency determined by .

Therefore, the frequency interval between channels of television broadcasting,
For example, if the delay time 7 is selected as ec in accordance with the mother MHz, and the frequency is set to be approximately at the center of the frequency band that includes those channels, the signal is detected from the input of the SAW element 2.

The frequency characteristics up to the output of the amplifier circuit 3 can be made as shown in Figure 3, and 6 (N-2) and 6 (N-1)
), Iso, 6(N+1), and 6(N12) can be made to correspond to the frequency of the local oscillation output necessary to receive the broadcast of each channel. Therefore, when the tuned voltage sweep circuit 8 starts the sweep operation and increases the frequency of the local oscillator of the tuner 1, the output of the detection/amplification circuit 3 has a frequency of 6 (N-2) as shown in FIG. ...6
Each time the frequency of the local oscillator reaches each of the frequencies of The frequency of 6(N-
It is possible to know which frequency from 2) to 6 (N+2) has been reached.

Therefore, when the channel number input from the keyboard switch 5 is 1, the counter 7 is preset to 1, so the frequency of the local oscillator is 6 (N-2) MH.
z and one pulse is applied from the waveform shaping circuit 4, the counter 7 immediately stops counting, issues a count end signal, stops the sweep operation of the tuned voltage sweep circuit 8, and lowers the local frequency to 6. (N-2) Fixed to M ratio.

Therefore, if N is determined in advance so that the tuner can receive broadcasts with channel number 1 when the local frequency is 6 (N-2) MHz, by inputting channel number 1 with keyboard switch 5, tuner 1 can be received. will automatically tune to the broadcast of channel number 1. When channel number 3 is input to the keyboard switch 5 of the same machine, the initial value of the counter 7 is reset to 3, and when three pulses are applied from the waveform shaping circuit 4, that is, the local oscillation frequency is MHz. At this time, a count end signal is generated, the sweep operation of the tuned voltage sweep circuit 8 is stopped, and the local oscillation frequency is fixed at Iso M so that the broadcast of channel number 3 can be received.

The same applies to other channel numbers.

In this way, according to the channel selection device shown in FIG.
By setting the characteristics of the W element 2 appropriately, input the channel number to the keyboard switch 5 for any channel in any frequency band (however, the frequency intervals between channels must be approximately equal). Since electronic tuning tuners were put into practical use, they became widely adopted, making it easy to tune into television receivers, FM tuners, etc., as well as accurately and quickly. It has made it possible to select stations. However, in the channel selection device shown in FIG. 1, the starting point of the pulse counting operation by the counter 7 is determined by the level difference due to the bandpass characteristic of the SAW element 2. This system has the disadvantage that it malfunctions when the output level of the local oscillator changes due to fluctuations, making it difficult to select the correct channel.

That is, assuming that the pulse counting operation by the counter 7 is performed for inputs equal to or higher than the count level CL in FIG. The level of the pulses from 2000 to 2000 also decreased, and the force counter 7 could not start counting when it was around 6(N-2)M, and the next 6(N-1)
Counting starts from MHz, and the input channel number is shifted by one channel higher than the input channel number.

On the other hand, when the output of the local oscillator increases, the selected channel will shift to a lower level.

Furthermore, the count level also changes due to fluctuations in the power supply voltage, making the operation even more unstable.

Therefore, it must always be properly adjusted.
In some cases, there is a drawback that an additional configuration is required to reduce fluctuations in the power supply voltage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a channel selection device that eliminates the drawbacks of the prior art described above and can always perform accurate channel selection operations.

In order to achieve this object, the present invention is characterized in that the timing at which counting starts is determined by the frequency of the local oscillator.

Embodiments of the present invention will be described below with reference to the drawings. Figure 4 shows an embodiment of the present invention, with the same parts as in Figure 1,
Alternatively, equivalent parts are given the same numbers, and detailed explanation thereof is omitted here, with reference to the explanation regarding FIG. 1.

In FIG. 4, 12 is a clock pulse generation circuit; 13 is a clock pulse generation circuit;
, 14 is a counter, 15 and 16 are comparators, 17 is a storage device, 18 and 22 are RS flip-flops, 19 is an integration circuit, two voltage conversion circuits, and 21 is a gate circuit 23
is an AND circuit, and 24 is a brisset switch. In the embodiment shown in FIG. 4, the tuning voltage pull-out circuit 8 shown in FIG. 1 is constituted by a digital circuit, and the bandpass characteristic of the SAW element 2 is made sufficiently wide.

Further, counters 3 and 14 are of 12 bits.

Next, the operation of this device will be explained. First, to describe the tuning voltage sweep operation, a channel number is input to the keyboard switch 5.

For example, when a pushbutton corresponding to a channel number is pressed, the counter 14 is reset and the gate circuit 21 is opened by a start signal. On the other hand, since the counter 13 performs counting operation by the pulse from the clock pulse generation circuit 12, the operation of generating carry-out output CO every time the count number N exceeds 4095 and returning the count contents to zero is repeated. There is.

Therefore, the counter 14 remains reset from the time the gate circuit 21 opens until the output CO of the counter 13 is generated, and its count remains at zero.

Therefore, just before the gate circuit 21 opens, the counter 13
Immediately after the output CO appears, the counter 1
Both counts 3 and 14 become zero, the comparator 15 outputs an output, and the RC flip-flop (hereinafter referred to as FF) 18 is reset. This state is shown in FIG. 5a. That is, since the bit signal from the output CO of the counter 13 and the IJ set signal from the output of the comparator 15 are applied almost simultaneously to the FF 18 one after another, the FF 18 remains reset. Next, the counter 13 counts the clock pulses, and when it reaches one cycle from 0 to 4095, an output appears on the output CO, and FF1
8 is set and added to the counter 14 through the gate circuit 21, making the count content 1.

Therefore, when the first clock is reached and the count content of the counter 13 becomes 1, the comparator 15 outputs an output and the FF 18 is reset.

This situation is shown in Figure 5b. Furthermore, when the counter 13 finishes counting one cycle thereafter, the output CO
appears, the FF 18 is set again, and the counter 14 becomes 2.

Then, since the counter 13 becomes count 2 at the second clock, the comparator 15 generates an output indicating that the count contents of the counters 13 and 14 match, and resets the FF 18. This situation is shown in Figure 5c. Below, it operates in the same way, and the counter 13 is 0 to 40.
Every time one cycle of counting up to 95 is completed, a carry-out output CO is generated, the FF 18 is set, and the count contents of the counter 4 are incremented by 1.

Therefore, the period from when the FF 18 is set to when it is reset increases for each period of the clock pulse, and this state is as shown in FIGS. 5d and 5e.

Therefore, the output of this RS flip-flop 18, that is, the pulses shown in FIGS.
A voltage that increases linearly with time as shown in FIG.

Since the voltage from the voltage conversion circuit 20 is applied to the local oscillator of the box-tuned tuner 1, the frequency of the local oscillator can be uniquely determined by the count N of the counter 14.

That is, in general, if the count content of the counter 14 is N and the reference voltage of the voltage conversion circuit 20 is E, the output voltage (
Tuning voltage) V is v=XE.

Therefore, when N is determined, the tuning voltage V is determined, and thereby the frequency of the local oscillator of the electronically tuned tuner 1 is determined, and in the end, the frequency of the local oscillator can be determined by N. In other words, in the embodiment shown in FIG. 4, the tuning voltage sweep circuit consists of the clock pulse generation circuit 12, the counters 13, 14, the comparator 15, the RS flip-flop 18, the integration circuit 19, the voltage conversion circuit 20, and the gate circuit 21. The frequency of the local oscillator can be accurately determined digitally from the contents of the counter 4.

Therefore, the channel selection operation will be explained next.

As already explained, when the channel number to be selected is input using the keyboard switch 5, the counter 13
, 14, etc., the tuning voltage switching operation starts, and the local oscillation frequency of the tuner 1 increases at a speed arbitrarily determined by the period of the clock pulse.
Through the amplifier circuit 3 and waveform shaping circuit 4, a pulse output appears every time the frequency corresponding to the frequency band in which the channel to be selected exists is reached, and a pulse output is generated by the keyboard switch 5.
has been reset and therefore no signal is applied to the AND circuit 23 from the FF 22, so the counter 7
No pulses are supplied from the detection/amplification circuit 4 to .

Therefore, the channel number preset from the keyboard switch 5 via the encoder 6 is maintained as an initial value in the power counter 7.

On the other hand, when the count content N of the counter 14 reaches a predetermined value, the value N is stored in advance in the storage device 17 by the reset switch 24.

When a channel number is input to the keyboard switch 5, a signal is applied to the input of the storage device 17, and the stored contents are applied to the comparator 16. For example, looking at television broadcast channels in Japan, the local oscillation frequency for one channel is 15 MHz, and the SAW element 2
If the characteristics of the comb-shaped filter according to
, 15+MHb, 158MHz, . . . Therefore,
Prior to use, operate the keyboard switch 5 arbitrarily,
When the tuning voltage reduction operation is started and the local oscillation frequency from the tuner reaches about 147M, that is, about XM lower than the frequency of the lowest channel, the preset switch 24 is closed, and the count content N of the counter 14 at that time is is stored in the storage device 17. So, going back to the previous explanation, when you operate the keyboard switch 5 and enter the channel selection operation, at first, the signal is not applied to the AND circuit 23 from the FF 22, so the Kawanta 7 does not start operating. As the tuning voltage sweep operation progresses and the local oscillation frequency reaches 147 MHz, the count number N of the counter 14 matches the number N stored in advance in the storage device 17, so the comparator 16 outputs Occur.

Therefore, the output from this comparator 16 is FF2
The signal is supplied to the set input of No. 2, the FF 22 is set, and the signal is given to the AND circuit 23.

As a result, the pulse from the SAW element 2 is applied to the counter 7 from the detection/amplification circuit 3 via the AND circuit 23, and the counter 7 starts counting down. Repeat this action in the sixth
This will be explained using figures.

As the local oscillation frequency increases, the output from the SAW element 2 to the detection/amplification circuit 3 appears as shown in FIG. 6a, and this output produces a pulse as shown in FIG. It is appearing.

When the frequency reaches 147 MHz, the FF 22 is set by the output of the comparator 16, and pulses are supplied to the counter 7 from when the frequency reaches 15 MHz as shown in FIG. Therefore, when the local oscillation frequency reaches 15 MHz when the channel number input from the keyboard switch 5 is channel 1, and 158 MHz when it is channel 2, a count end signal is applied from the counter 7 to the gate circuit 21 as a stop signal. Then, the gate circuit 21 is closed and the tuning voltage reduction operation is stopped, and the voltage conversion circuit 20 continues to supply a constant voltage corresponding to the frequency to the local oscillator of the tuner 1, and the channel selection operation is completed. .

That is, as a result, the count content of the counter 4 is maintained at a value corresponding to the local oscillation frequency of the selected channel, and the RS flip-flop 18 repeats setting and resetting at a corresponding period, and the voltage conversion circuit 20
The output of is held at the tuning voltage corresponding to that channel. In this embodiment, counting is always started when the local oscillation frequency reaches just before the maximum value to be counted by the SAW element 2, and the bandpass characteristic of the SAW element 2 is not utilized. It is possible to completely eliminate the drawback of the conventional technology that the timing of starting counting is out of order due to level fluctuations. Additionally, since the local oscillation frequency reaches a predetermined value to determine when to start counting for channel selection, the storage device must accurately store the frequency value. , since the frequency value is given by the digital value of count 14, it is possible to memorize the accurate frequency value simply by storing this digital value in the storage device 17, and the operation is always accurate. It will be held in Now, in the embodiment shown in FIG. 4, the frequency band is configured as one band to simplify the explanation, but in actual television broadcasting, the frequency band is, for example, the VHF low band (1 to 3 bands). It has a three-band configuration: VHF high band (channels 4 to 12), and UHF band (channels 13 to 62).

Therefore, in applying the channel selection device according to the present invention, a band determination circuit that determines the frequency band based on the input channel number, an address specified by the band determination circuit, and the count contents of the counter 14 are stored at the specified address. However, it is sufficient to use a storage device that allows reading from that address.

Of course, each van W has its own storage device independently, that is, 3
In this case, the lowest local oscillation frequency in the VHF high band is 23 MHz (4 channels). Since this is not a multiple of 6, the maximum value of the output occurs at an interval of Mizukawa z, and a comb-shaped filter must be constructed from SAW elements.

And the maximum value is..., 222, 224, 226, 228
, 23mMHz, . . . Therefore, when the local oscillation frequency reaches 228MHz, the brisset switch 24 is closed and the count contents of the counter 3 are stored. As a result, the counter 7 starts counting from exactly 228 MHz, 226, 228, 23
Since the pulse will be output from the AND circuit 23 at the maximum value of 0 MHz, "by dividing this pulse by 3, add a pulse by 7' to the counter only when it reaches 23 MHz (4 channels). "238MHz (5 channels), 242MHz"
Counter 7 pulses at z (6 channels),...
You can add it to

Also, even in UHF vans, the lowest local oscillation frequency is 5.
Since the ratio is 30M (13 channels), which is not a multiple of 6, it is sufficient to use a SAW element and a divide-by-3 circuit, which is a comb-shaped filter with a 2MHz interval, in the same way as above. In this case, the frequency value to be stored by closing the reset switch 24 is 529 MHz.

It goes without saying that the VHF low band shown in the embodiment of FIG. 4 can also be implemented in the same manner as the 2 MHz comb filter configuration.

FIG. 7 shows an example of the SAW element 2 when the three frequency values are divided into three bands as described above. Here, 25 is a VHF electronic tuning tuner, and 26 is a UHF electronic tuning tuner.

The SAW element 2 consists of three parts, one for VHF low band, one for VHF high band, and one for UHF high band.
The low band and high band elements of F have a common input, and can all have a common output. This is because the elements for each band do not constitute a comb-type filter within that band, and therefore do not have a pass band width for the frequencies of other bands 4. Another embodiment of the invention is shown in FIG.

In this embodiment as well, the same or equivalent parts as in the embodiment of FIG. 4 are given the same numbers, and parts that are not directly related are omitted.

In FIG. 8, 27 and 28 are comb-shaped filters with 2 MHz spacing and Akigawa z spacing, respectively, by SAW elements, 29,
30 is a detection 3 amplifier circuit, 31 and 32 are waveform shaping circuits, 3
3, 34, and 36 are band circuits, and 35 is an RS flip-flop.

Next, the operation of this device will be explained with reference to FIG.

In this embodiment, the pulses produced by the comb-shaped filter having the Mizumachi z interval and the pulses produced by the comb-shaped filter having the 9 MHz interval are ANDed to obtain the pulses having the a MHz interval, thereby facilitating the presetting operation, and The output waveform of the detection and amplification circuit 29 connected to the comb-shaped filter 27 with a 2M ratio is determined by the waveform shaping circuit as shown in Figure 9a. The output waveform of 31 is as shown in Figure 9b, and the output waveform of
Detection of comb-shaped filter 28.

The output waveforms of the amplifier circuit 30 and waveform shaping circuit 32 are shown in FIG. 9c.
, d. Therefore, the output of the AND circuit 33 has a waveform as shown in FIG. 9e. This embodiment is an example in which a UHF band radio is applied, and the frequencies appearing in each waveform have values as shown in the upper part of FIG.

In this embodiment, the preset switch 24 may be closed when the local oscillation frequency reaches between 516 and 522 MHz. During tuning, when the local oscillation frequency reaches the above value, the output from the comparator 16 is applied to the RS flip-flop 22, so this flip-flop 22 is set, and the output from the AND circuit 33 is added to the RS flip-flop 22. The RS flip-flop 35 is set.

This puts the AND circuit 36 in a state where it can be gated,
Since the output of the waveform (FIG. 9b) from the waveform shaping circuit 31 begins to be supplied to the counter 7, the counter 7 starts counting from the pulse when the local oscillation frequency reaches 52 Mizuta z.

Therefore, if the counter 7 is provided with a function to ignore the first two pulses, it will start counting from the pulse with the local oscillation frequency of 52 Atomachi z (the shaded pulse in FIG. 9b). Therefore, by restricting this pulse by three minutes, it is possible to stop even from 530 MHz, which is the local oscillation frequency of the first channel (channel 13) in the UHF band. In this way, in the embodiment shown in FIG. 8, pulses with intervals of aM are used, so the setting of the frequency to be preset does not need to be coarse, the presetting is easy, and the temperature and humidity characteristics of the local oscillation frequency are improved. This has the effect of increasing the margin for

Still another embodiment of the present invention is shown in FIG.

In the embodiment shown in FIG. 10, the same or equivalent parts as in the embodiment shown in FIG. It has been omitted.

This embodiment differs from the embodiment shown in FIG. 4 in that the reset output of the storage device 17 is added to the reset input of the counter 14, which allows for tuning during channel selection. Rather than starting a voltage sweep, it starts from a preset voltage. The operations during presetting are the same as those shown in Fig. 4.

At the time of channel selection, a preset signal is applied from the keyboard switch 5 to the counter 14, and the preset contents retrieved from the storage device 17 are preset to the counter 14.

Therefore, the tuning voltage sweep operation starts from this preset voltage, a voltage that sweeps up from the preset voltage is applied to the electronic tuning tuner 1, and the local oscillation frequency starts from the preset value. Then, this local oscillation frequency is immediately detected and detected by the SAW element 2.
The signal V is supplied to the counter 7 via the amplifier circuit 3 and the waveform shaping circuit 4, where it is counted and a channel selection operation is performed. Therefore, the count start time of the counter 7 is accurately defined by the preset local oscillation frequency, and the disadvantage of the prior art that the count start time is inaccurate can be eliminated. In addition, in the embodiment shown in FIG. 10, as in the embodiments shown in FIGS. 4, 7, and 8, 3
Of course, it is possible to use a band or a configuration using a plurality of comb-shaped filters with different frequency intervals.

Further, in the above implementation series, the tuner for a television receiver was mainly explained, but it goes without saying that it can be implemented similarly as an FM tuner.

As explained above, according to the present invention, by providing the storage means, it is possible to accurately define the start of the counting operation for the channel selection operation using the local oscillation frequency. There is no malfunction caused by fluctuations in the output level of the local oscillator, unlike when using the bandpass characteristic of the oscillator, and stable tuning operation can be obtained. Furthermore, by using a plurality of SAW elements to configure two sets of comb-shaped filters with different characteristics, it is possible to facilitate the presetting operation and to reduce the influence of temperature and humidity on the local oscillation frequency. I can do it.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a channel selection device using a surface acoustic wave element, Fig. 2 is a schematic block diagram of the surface acoustic wave element, Fig. 3 is an output characteristic diagram of the detection/amplification circuit, and Fig. FIG. 4 is a block diagram of a surface acoustic wave tuning device according to an embodiment of the present invention;
5a to 6f and 6a to 6c are waveform diagrams for explaining the operation thereof, FIG. 7 is a block diagram showing the configuration of a comb-shaped filter using surface acoustic wave elements, and FIG. 8 is a diagram showing another example of the present invention. A block diagram of a surface acoustic wave tuning device according to an embodiment, FIGS. 9a to 9e are waveform diagrams for explaining its operation, and FIG. 10 is a surface acoustic wave tuning device according to still another embodiment of the present invention. FIG. 2 is a block diagram of the device. 1... Electronic tuning tuner, 2, 27, 28. ．．・．．
．．・Surface acoustic wave element, 3, 29, 30...Detection/amplification circuit, 4, 31, 32... Waveform shaping circuit, 5
...Tap keyboard switch, 6...Encoder, 7
... Counter, 12 ... Clock pulse generation circuit, 13, 14 ... Force counter, 15, 16 ... Comparator, 17 ... Memory device, 18, 22, 35.
...RS flip-flop, 19...Integrator circuit, 200...Voltage conversion circuit, 21...
- Gate circuit, 23, 33, 34, 36...AND circuit, 24...brisset switch. 2 figures, 3 figures, 5 figures, 4 figures, 7 figures, 5 figures, 8 figures, 0 figures

Claims (1)

[Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator, a tuned voltage sweep circuit that sweeps the oscillation frequency of this local oscillator, a surface acoustic wave comb filter coupled to the output of the local oscillator, and an output of this filter. In a surface acoustic wave tuning device that includes a detector for inputting a signal and performs tuning by counting output signals of the detector, the tuning voltage sweep is performed when the oscillation frequency of the local oscillator reaches a predetermined value. A memory circuit is provided for storing the output voltage from the circuit, and the output voltage from the tuned voltage sweep circuit is compared with the voltage stored in the memory circuit during channel selection operation, and the oscillation frequency of the local oscillator reaches a predetermined value. A surface acoustic wave tuning device characterized in that the surface acoustic wave tuning device is configured to start counting the output signal of the detector from the moment the wave detector reaches the point where the wave detector reaches the point where the surface acoustic wave tuner reaches the target position.