JPS6036652B2 - Tuned voltage sweep circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuning voltage sweep circuit in a tuning device using a surface acoustic wave element mainly used in televisions and FM tuners.

The example shown in FIG. 1 is known as a channel selection device using a surface acoustic wave device (hereinafter abbreviated as a SAW device).

In the figure, 1 is an electronic tuning tuner having a voltage-controlled local oscillator, and 2 is an input electrode 9 as shown in FIG. 1b.
A SAW element 3 has two output electrodes 10 and 11 connected to each other and constitutes a comb-shaped filter. 4 is a waveform shaping circuit for converting the output of the detection/amplification circuit 3 into pulses; 5 is a keyboard switch for inputting the channel number to be selected; 6 is for inputting the channel number input from the keyboard switch 5; 2
The encoder 7 for evolution is preset with the output of the encoder 6, and the waveform shaping circuit 4 uses that value as an initial value.
A counter 8 counts down the number of pulses sent from the counter 7. When the channel number is input to the keyboard switch 5, the exposure pressure sweep is started.
This is a tuned voltage bridge circuit in which voltage bridge is stopped by the count end signal generated by . First, the operation of the final channel selection device will be described.

When a desired channel number is input to the keyboard switch 5, it is converted into a binary number by the encoder 6 and preset in the counter 7. On the other hand, upon input of the channel number, the tuning voltage sweep circuit 8 starts voltage sweeping, and as a result, the local oscillation frequency of the electronic tuning tuner 1 gradually increases from a certain frequency. This local oscillation output is input to the SAW element 2. The SAW element 2 has a structure as shown in FIG. 2, and the input local oscillation output is converted into a surface wave at the input electrode 9 and reaches two output electrodes 10 and 11. The surface waves are converted into electrical signals again at the electrodes, but the signals converted at the electrodes 11
Since the propagation distance is longer than the signal converted by the electrode 10, it has a certain delay time 7 compared to the signal converted by the electrode 10. Therefore, the signal voltage converted by the electrode 10 is Aej■t(=2
When expressed as (t-7), the signal voltage at the electrode 11 is multiplied by (t-7) of Aej.

Since both electrodes are connected to each other, the output voltage V at the output terminal of the SAW element 2 is
t-d)} ...(1), and when the amplitude is detected and amplified by the detection amplifier circuit 3, the output voltage Vo becomes Vo=
G・IVl (G: degree of amplification) Ni GA no 2 (10 COS no 1) ■.

Therefore, the frequency of Vo becomes maximum at 〆=N/7 (N: integer)...'3'', and the frequency interval △〆 becomes 1/digit.

In television broadcasting stations, in many cases the local oscillation frequency exists every MH2, so if 7=1/6 microseconds is selected, the output voltage will be maximum every aYH2.
Furthermore, since the SAW element 2 itself has a bandpass characteristic in which the center frequency is v/2d, where d is the electrode spacing and v is the velocity of the surface wave, the frequency characteristic of the output voltage Vo is expressed in decibels as shown in Figure 3. and the peak point is equivalent to one channel. Therefore, the band width of the SAW element 2 is set so that the output of the detection amplifier circuit 3 is pulsed by the waveform shaping circuit 4 from the peak point corresponding to the lowest local oscillation frequency, and the local oscillation frequency is swept to shape the waveform. By counting the number of pulses sent from the circuit 4, it is possible to know how many broadcast stations have passed. Therefore, the output of the waveform shaping circuit 4 is sent to the counter 7. The counter 7 counts down the output pulses of the waveform shaping circuit 4 using the channel number input from the keyboard switch 5 as an initial value, and generates a count end signal when the count ends. This signal is applied to the tuning voltage sweep circuit 8' as a sweep stop signal. As a result, the local oscillation frequency of the electronically tuned tuner is maintained at a desired value, and tuning is completed. The example shown in FIG. 4 has been used as a tuning voltage pull-out circuit in the surface acoustic wave tuning device as described above.

In FIG. 4, the same parts as in FIG. 1 are designated by the same numbers. The tuning voltage sweep circuit 8 includes the clock pulse generation circuit 1
2, counters 13, 14a, 14b, comparator 15
, R is set by the carry-out output of the force counter 13 and reset by the matching number of the comparator 15.
S flip-flop 16, voltage conversion circuit 17, integration circuit 18, low-speed switching signal generation circuit 19 that generates a signal to switch to low-speed sweep based on the data of counter 7, during high-speed edge, A, B, and C are closed, respectively. The switch circuit 20 opens, closes, and closes during low-speed sweep, respectively, and the counter 1
It is comprised of a gate circuit 21 that sends the carry-out output of No. 3 to a switch circuit 20 and prevents it from passing after a count end signal is generated. The low-speed switching signal generation circuit 19 is a circuit that generates a signal for switching to low-speed sweep based on the data of the counter 7, and has a decoder and a flip-flop. It detects that the station is several stations ahead of the station, sets a flip-flop, and then switches to low-speed sweep. That is, the data of the counter 7 is input to the decoder, and from the initial value of the counter 7 set by the keyboard 5, according to the output from the waveform shaping circuit 4,
It counts down, and when the value of the down counter 7 reaches a predetermined value, the output of the decoder is switched, the output of the flip-flop connected to the decoder is switched, and the sweep speed of the tuner is adjusted according to the output of the flip-flop. Switch to low speed. At this time, the decoder is set so that the output is switched several stations before the target station, for example, if the down counter indicates ``3'' before the third station, the output is switched to ``1''.Next, this circuit The operation will be explained with reference to FIG.

In Figure 5, the upper numbers 0, 16, 32,...I
Q, IG+,, IQ+2... are the data values of the force counter 13, and the leftmost numbers are the counters 4a, 14b (
Both are regarded as a 12-bit counter). When a channel number is input to the keyboard switch 5 in FIG. 4, the counter 14 is reset and the data becomes 0, although the arrow is omitted, and the gate circuit 21
becomes the optimal state. Moreover, in order to speed up the channel selection time, only A of the switch circuit 20' is closed, and the counter 13 is closed.
A carry-out signal is sent to the counter 14b. The counter 13 counts one cycle from 0 to 4095, and when all bits become 0, generates a carry-out signal. Before this occurs, the data in the counter 14 is 0. Therefore, when the data of counter 13 is 0, comparator 1
5 generates a match signal and RS flip-flop 16 is reset. Therefore, the Q of the RS flip-flop 16 is
The output remains at a logic 0 level. This is shown in Figure 5i). The counter 13 counts the first cycle and generates a carry-out signal when all bits become 0. This signal sets the RS flip-flop 16, and it is sent to the counter 14b via the gate circuit 21 and switch circuit 20. Therefore, when the counters 14a and 14b are regarded as 12-bit counters, the data value becomes 16 in 1G Hayabusa. So counter 1
When the data of 3 becomes 16, the comparator 15 generates a match signal, which causes the RS flip. The button 16 is reset. Therefore, the Q output waveform becomes as shown in FIG. 5 ii). Thereafter, each time the counter 13 counts one cycle, the data on the counters 4a and 14b increases by 16.
Therefore, the data of the counter 13 set by the RS flip-flop 16 increases by 16. Therefore, the Q output waveform becomes as shown in FIG. 5 iii) and iv) below. If such a Q output waveform is converted into an arbitrary voltage by the voltage conversion circuit 17 and integrated by the integration circuit 18, the tuning voltage will gradually rise as shown by A in FIG. However, as shown by the broken line, the actual output voltage is the digital value of the voltage (shown by the solid line), Vd = 4 6E --- (41
There is a slight delay due to the integration circuit 18 compared to the standard value.

As the tuning voltage increases, the channel count of the counter 7 progresses, and when the desired station is near (for example, one station before), the data of the counter 7 becomes 1, so the low-speed switching pulse is generated from the low-speed switching signal generation circuit 19. This causes switches A, B, and C to open, close, and close, and the counters 4a,
The data 14b increases by 1 every cycle of the counter 3. Therefore, the Q output waveform of the RS flip-flop 16 becomes as shown in iv) to ") in FIG. 5, and the tuning voltage is swept with high precision and at low speed in the vicinity of the desired station. As shown in the figure below, when the bridge is pulled at a low speed, a count end signal is finally generated from the counter 7, which closes the gate circuit 21 and fixes the data in the counters 14a and 14b.Therefore, tuning at the desired station is possible. The voltage sweep stops. However, in such a tuned voltage sweep circuit, the count end signal is generated when the actual output voltage is the value represented by D in Figure 6, and the digital Therefore, even after the count end signal is generated, the actual tuning voltage increases by ΔV until it matches the digital value as shown by C, causing oversweep by this value.Moreover, If the ripple of the tuning voltage is large when the sweep is stopped, beats will occur on the screen, so the integration constant of the integrating circuit 18 must be increased, and therefore the voltage that causes overdrawing will become large.Especially in the case of the UHF band. This oversweep is large enough to pass two or three broadcast stations. Therefore, in order to eliminate this oversweep, after the count end signal is generated, the data values of the counters 4a and 14b are changed to the oversweep voltage △. It is possible to reduce the frequency by a value equivalent to V. However, as shown in Figure 7, at stations with low tuning voltage, the local oscillation frequency change per unit tuning voltage change is large, and at stations with high tuning voltage, this is small. Therefore, when the number of stations swept at low speed is constant, the low speed sweep time is short for stations with low tuning voltage, so the count end signal is generated before the delay during high speed sweep is fully recovered. Therefore, the oversweep voltage △V is large. This is shown in 1 in Fig. 8. Conversely, at a station with a high tuning voltage, the oversweep voltage △V is large.
As shown, since the low-speed sweep time is long, the delay during high-speed sweep is sufficiently recovered, and the saturation state during low-speed sweep is reached. For this reason, the oversweep voltage ΔV was 4.0% smaller, and the overbridge voltage varied depending on the tuning voltage. SUMMARY OF THE INVENTION It is an object of the present invention to eliminate the drawbacks of the above-mentioned conventional techniques and to provide a tuned voltage sweep circuit that is free from oversweep.

In order to achieve the above-mentioned object, the present invention reduces the delay of the tuning voltage with respect to the digital value by reducing the integration constant of the integrating circuit when the tuning voltage is swept over a high distance.

In the vicinity of the desired station, the integral constant is increased and the delay is reduced to a low speed, so that the delay remains constant regardless of the tuning voltage. When the sweep stop signal is generated, the tuning voltage is reduced by the amount of delay. An embodiment of a tuned voltage sweep circuit according to the present invention will be described below with reference to the drawings.

FIG. 9 is a diagram showing an embodiment of the tuned voltage bridge circuit 8 according to the present invention, an electronic tuning tuner, a keyboard switch 5, and a counter 7 connected thereto. Parts are labeled with the same number. In FIG. 9, 22 is a switch, 23' and 24 are resistors,
A pulse generating circuit 25 generates a preset number of pulses in response to generation of a count end signal from the counter 7, and counters 14a and 14b are up/down counters. In this embodiment, the circuit of FIG. 4 operates until the count end signal is generated, except that the switch 22 is closed when sweeping the tuning voltage at a high speed, and is opened when sweeping the tuning voltage at a low speed. is exactly the same.

Since the switch 22 is closed during high-speed sweep, the integration constant of the integration circuit 18 becomes small, and the delay between the actual output voltage and the digital value is small. As the tuning voltage increases, a low-speed switching signal is generated from the low-speed switching signal generation circuit 19 in the vicinity of the desired station, and the tuning voltage becomes striped at low speed and with high accuracy. At the same time, a switch 22 is opened in the integration circuit 18 to increase the integration constant and eliminate ripples. At this point, the difference between the actual output voltage and the digital value is small, so even if the number of stations swept at low speed is the same as in the case of Fig. 4 (d), the delay during high speed sweep can be sufficiently recovered regardless of the tuning voltage. , the saturation state can be achieved during low-speed pail pulling. Therefore, the voltage delay ΔV remains constant regardless of the tuning voltage. Thereafter, a count end signal is generated, and at the same time the gate circuit 21 is closed by this signal, the counter 14a is
, 14b are used as down counters, and a predetermined number M of pulses are generated from the pulse generation circuit 25, and the delayed voltage △V
is decreased by the data value corresponding to . As a result, the output voltage is maintained at the value at the time when the count end signal is generated, and oversweep can be eliminated. Note that the number M of pulses generated from the pulse generation circuit 25 is Δv=6·E.
・・・． ...(from 5', M = pole brush here) -
-... (Select the integer value closest to 61.

Further, the state of change in the tuning voltage at this time is shown in FIG. As described above, according to the present invention, it is possible to eliminate oversweep, which is a drawback of conventional tuned voltage sweep circuits, and
It is possible to provide a tuning voltage sweep circuit that can stop sweeping the tuning voltage at the optimum tuning point. When applied to televisions, the performance of not only VHF but also UHF can be dramatically improved, and the effects of the present invention are extremely large.

[Brief explanation of the drawing]

FIG. 1 shows a surface acoustic wave tuning device to which the present invention is applied. Figure 2 is a block diagram of the SAW element, Figure 3 is a characteristic diagram of the device in Figure 1, Figure 4 is a circuit diagram of the slave tuning voltage sweep circuit, Figures 5 to 8 are 4 is a characteristic diagram of the circuit, FIG. 9 is a circuit diagram of an embodiment of the present invention, and FIG. 10 is a characteristic diagram of the circuits of FIGS. 4 and 9. 1: Electronic tuning tuner,
2: SAW element, 3: Detection amplifier circuit, 4: Waveform shaping circuit, 5: Keyboard switch, 6: Encoder, 7, 13
, 14a, 14b: counter, 8: tuning voltage pull-out circuit,
9, 10, 11: electrode, 12: clock pulse generation circuit, 15: comparator, 16: RS flip-flop,
17: voltage conversion circuit, 18: integration circuit, 19: low-speed switching signal generation circuit, 20: switch circuit, 21: gate circuit, 22: switch, 23, 24: resistor, 25: pulse generation circuit. Figure 7, 6, figure 8, figure 8, younger brother, figure 2, figure 3, figure 4.

Claims (1)

[Claims] 1. An electronically tuned tuner having a voltage-controlled local oscillator; comprising pulse generating means for generating a pulse signal whose pulse width increases with time; and an integrating circuit connected to the pulse generating means for integrating the pulse signal; a tuned voltage sweep circuit that supplies a DC voltage integrated by the circuit to a control input terminal of the local oscillator; a surface acoustic wave comb filter that is connected to the electronically tuned tuner and receives the oscillation output of the local oscillator; a detection circuit connected to the filter and detecting the output of the filter; a counter connected to the detection circuit counting the output signal of the detection circuit and supplying the count output to the tuned voltage sweep circuit;
In a tuning device that stops sweeping by the tuned voltage sweep circuit when the counter has counted a preset number of counts according to the desired station to tune to; Switch the time constant,
A time constant switching means for setting a time constant in the vicinity of the desired station to be selected to be larger than a time constant at the time of starting the selection, and a time constant switching means for switching the sweep speed of the tuned voltage sweep circuit to change the sweep speed in the vicinity of the desired station to be selected. 1. A tuned voltage sweep circuit comprising: sweep speed switching means for setting the sweep speed to a lower speed than the sweep speed at the start of channel selection.