JPS6248930B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuning voltage output circuit suitable for use in channel selection devices such as televisions and FM tuners.

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. Figure 1 is a diagram showing its configuration, in which 1 is an electronic tuner and 2 is an electronic tuner.
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 It is a number display device. Here, SAW element 2
This will be explained using FIG. 2. LiNbO ₃ and
An input electrode 12 and output electrodes 13 and 14 connected to each other are arranged on a piezoelectric substrate such as LiTaO ₃ , and the local oscillation output from the electronic 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 placed at different distances from the input electrode 12,
The signals at both electrodes have a phase difference from each other. Therefore, if we write the signal at the output electrode 13 as V ₁ =Ae ^j 〓 ^t (ω=2π: frequency), the signal at the output electrode 14 will have 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- 〓 ⁾ . These amplitudes |V| are |V|=A|e ^j 〓 ^t +Ae ^j 〓 ^(t- 〓 ⁾ |= A√2(1+), and this value is ω=2N〓/τ, that is, =N/τ( When N: an integer), the maximum value is 2A; when ω=(2N+1)〓/τ, that is, = (N+1/2)/τ (N: an integer), the minimum value is 0. The frequency interval Δ that takes the maximum value is equal as Δ=(N+1)/τ−N/τ=1/τ (τ: constant). Therefore, the passband of this SAW element 2 is the local oscillation frequency of each TV broadcasting band (VHF low band, VHF high band, UHF band). 4 to 12 ch.) 230 to 276 MHz UHF band (13 to 62 ch.) 530 to 824 MHz. If you select a pass band from a value 4 MHz lower than the first frequency, and set τ = 0.5 μsec, the first frequency will be displayed in decibels. A frequency characteristic as shown in Fig. 3 is 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 input and output of the elements for each of the three bands are connected in parallel, because each element has a passband only in its own band and can be treated independently of each other.

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,
At the output of the SAW element 2, the level of the local oscillation signal increases or decreases depending on the frequency characteristics 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 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. (See Figure 3) As a result, the data of counter 7 becomes 0,
Channel selection is complete.

The example shown in FIG. 5 is known as the tuning voltage sweep circuit 8 in the above-mentioned tuning device. In the same figure, 15 is an AFC voltage generation circuit;
6 indicates that the output of the AFC voltage generation circuit 15 is the center value (approximately
A voltage discrimination circuit 17 and 18 indicates a switch made of a transistor or the like, which detects whether the voltage is higher or lower than 6V), and the switch is turned on or off by the output of the voltage discrimination circuit 16. 19 is a resistor, and 20 is a capacitor. From the time the channel number is input to the keyboard switch 9 until the counter 7 generates the sweep stop signal, the switch 17 is
ON, switch 18 is turned OFF and capacitor 20
, and sweeps the tuning voltage. After the sweep stop signal is generated, the voltage discrimination circuit 16 outputs a high level H signal when the AFC voltage is higher than the center value, and a low level L signal when it is lower. This signal controls ON and OFF of switches 17 and 18, and when the AFC voltage is high, switch 17 is ON and OFF.
Switch 18 is OFF, when low, switch 1
7 is OFF and switch 18 is ON. Therefore, when the local oscillation frequency is lower than the normal tuning point because the tuning voltage is low, the AFC voltage is high, so the capacitor 28 is charged via the switch 17, and the tuning voltage becomes high. Conversely, when the local oscillation frequency is higher than the normal tuning point because the tuning voltage is high, the AFC voltage is low, so the capacitor 20 is discharged via the switch 18, and the tuning voltage becomes low. They held the same point.

However, when there are no broadcast waves, the AFC voltage has a constant value near the center value. For this reason, the switches 17 and 18 are fixed in either ON or OFF state, so the tuning voltage becomes 0V or 30V (maximum voltage) and cannot maintain a predetermined value. As a result, if the receiver passes through a tunnel or is affected by an airplane, the electric field changes.
I was no longer able to receive the channel I had been receiving and had to tune in again.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a tuning voltage output circuit capable of holding a tuning voltage.

In order to achieve the above-mentioned purpose, in the present invention, the AFC voltage discrimination point is changed from the conventional one value to two values, and the AFC voltage state is divided into three. It is characterized by having a state of retention.

Specific embodiments of the present invention will be described below with reference to the drawings. FIG. 6 is a circuit diagram showing a specific embodiment of the present invention, in which 21 to 33 are resistors, 34 is a diode, 35 is a 9V Zener diode, 36 is a 3V Zener diode, 3
7 to 41 are transistors, 42 is an RS flip-flop, and 43 is a voltage source from the AFC voltage generation circuit 15.
This is a switch circuit that changes the fixed voltage of AFC voltage and power supply voltage Ec (6V). Of these, the RS flip-flop 42 is set when a channel number is input to the keyboard switch 9, and is reset by a sweep stop signal from the counter 7, turning on the transistor 37 during that time. As a result, the transistor 38 is also turned on, charging the capacitor 20 and sweeping the tuning voltage. After the sweep is stopped, the diode 34 disconnects the RS flip-flop 42 from this system. Further, the Zener diode 35 and the transistor 37 constitute a 9V voltage determination circuit. AFC voltage generation circuit 1
When the AFC voltage of 5 becomes 9V or more, a current flows through the Zener diode 35, which is connected to the transistor 37.
The base current becomes the base current and turns on the transistor 37. At voltages below that, transistor 3
7 is OFF. Similarly, Zener diode 3
6 and transistor 39 constitute a 3V voltage determination circuit. When the AFC voltage exceeds 3V, current flows through the Zener diode 36, and the transistor 39
Turn on. At voltages below that, transistor 39
is OFF. The transistor 41 functions to once drop the tuning voltage to 0V when selecting a channel. When the channel number is input to the keyboard switch 9, the transistor 41 turns on, and the capacitor 2
The charge that was charged to 0 is discharged and the tuning voltage is increased.
Drop to 0V. As the pulse from the keyboard switch 9 falls, the transistor 41 becomes
The transistor 41 is turned off and disconnected from this system.

Note that it is preferable for the transistors 38, 40, and 41 to be constructed of field effect transistors (FETs) having a large non-conducting resistance for a UHF band channel.

Next, the operation of this circuit will be described. When a channel number is input to the keyboard switch 9, the transistor 41 is turned on and the tuning voltage is reduced to 0V. When the pulse from the keyboard switch 9 falls, the transistor 41 is turned off. Further, the RS flip-flop 42 is set and its Q output becomes a high level H, and the transistor 431 of the switch circuit 43 is turned on at this high level H. At this time, the power supply voltage is applied to the emitter of transistor 431.
Obtained by dividing 12V with resistors 433 and 434
Since a voltage of 6V is given, that 6V voltage is output to the collector, fixing the AFC voltage during sweeping to 6V. As a result, transistor 39
is turned on, and the transistor 40 is turned off. Also
Since the RS flip-flop 42 is set, the transistor 37 is turned on. Therefore, transistor 38 is also turned on, but transistor 40,
41 are all OFF, charge is gradually stored in the capacitor 20, and as a result, the tuning voltage is swept. During this time, counter 7
counts the output of the frequency divider circuit 6 a predetermined number of times and outputs a sweep stop signal after the count ends. This signal resets the RS flip-flop 42 and disconnects it from the system, and at this time the Q output of the flip-flop 42 becomes low belt L, so the transistor 431 of the switch circuit 43 is turned off. Therefore, the AFC output of the AFC voltage generation circuit 15 is transmitted to the respective voltage determination circuits, that is, transistors 37 and 39. After the sweep is stopped, if the tuning voltage is appropriate and the local oscillation frequency of electronic tuner 1 is a normal value, the AFC voltage is approximately 6V, so transistors 37 and 39 are
As a result, the transistor 38,
Both capacitors 40 are turned off to prevent charging and discharging of charges to the capacitor 20 and maintain its tuning voltage. Since the tuning voltage is high, when the local oscillation frequency is higher than the normal value and the AFC voltage becomes 3V or less, both transistors 37 and 39 are turned off, and as a result,
The transistors 38 and 40 are turned OFF and ON, respectively, to discharge the charge stored in the capacitor 20 and lower the tuning voltage. Also, because the tuning voltage is low, the local oscillation frequency is lower than the normal value, and the AFC
When the voltage is 9V or more, transistors 37 and 39 are both turned on, and as a result, transistors 38 and 40 are turned on and off, respectively.
Charge the capacitor 20 and increase the tuning voltage. This operation always provides the optimum tuning point.

In such a tuned voltage output circuit, when there is no broadcast wave, the AFC voltage will be around 6V, so
The state is the same as the case where the optimum tuning point has been obtained. For this reason, transistors 38, 4
0, both become OFF, and as a result, the voltage can be held.

Note that transistors 38, 40, and 41 are OFF.
However, due to leakage, capacitor 2
Charging and discharging is performed with respect to 0, and it may be difficult to maintain the tuning voltage. In this case, instead of bipolar transistors, the transistors 38, 40, and 41 can be made of elements with very large non-conducting resistance, such as field effect transistors (FETs), to extend the holding time.

Next, the reason why the AFC voltage is fixed to the output voltage (6V) of the switch circuit 43 during sweeping is as follows. If the tuning voltage is sweeping during tuning, it may pass through a channel with a broadcast station on the way. If there is no broadcasting station, the AFC voltage will be at the center value (approximately
6V), but when passing through a channel with a broadcasting station, the AFC voltage is within a specified range (generally 1V~
12V). Therefore, the transistor 39
OFF, and therefore the transistor 40 may be turned ON. Therefore, although the tuning voltage should gradually rise from 0V, it sometimes falls, and as a result, the detected waveform in the detection circuit 3 is disturbed, resulting in erroneous counting. To prevent this erroneous count, a fixed voltage of 6V is applied instead of the AFC voltage during sweep.

In the above description, an example using a SAW element has been described as a channel selection device to which the present invention is applied, but the present invention can also be applied to a channel selection device as shown in FIG. That is, 44 in Figure 7
45 is an intermediate frequency detection circuit that determines whether a regular intermediate frequency is obtained based on AFC voltage, etc.
is a synchronization signal detection circuit. This example is a so-called search type channel selection device, which sequentially selects broadcast waves one station at a time. At the time of tuning, the tuning voltage sweep circuit 8 is operated to sweep the tuning voltage applied to the electronic tuning tuner 1. Once the broadcast wave is available, the appropriate intermediate frequency and synchronization signals are generated. This is the intermediate frequency detection circuit 4
4 and the synchronization signal detection circuit 45, AND gate 46 performs an AND operation of the two, and applies the result to the tuning voltage sweep circuit 8 as a sweep stop signal. Now you can receive the next broadcast station. The present invention can be applied as is to a tuning voltage output circuit in such a tuning device.

As described above, according to the present invention, it is possible to provide a tuning voltage output circuit capable of holding a tuning voltage. Further, according to the present invention, even if the electric field changes or the broadcast wave is interrupted during reception, the tuning voltage of the channel is stably maintained, and there is no need to reselect the channel.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the first channel selection device to which the present invention is applied, Fig. 2 is a diagram showing the principle configuration of the SAW element, and Figs. 3 and 4 show the frequency characteristics of the SAW element. 5 is a block diagram showing a conventional example of a tuning voltage sweep circuit, FIG. 6 is a circuit diagram showing an embodiment of a tuning voltage output circuit according to the present invention, and FIG. 7 is a circuit diagram showing an embodiment of a tuning voltage output circuit according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1...Electronic tuner, 2...SAW element, 3...Detection circuit, 4...Amplification circuit, 5...Waveform shaping circuit, 7...Counter, 8...Tuning voltage sweep circuit, 9...Keyboard switch, 15...AFC voltage generation circuit, 20 ... Capacitor, 34... Diode, 35, 36... Zener diode, 37-41... Transistor, 4
2...RS flip-flop, 43...switch, 4
4...Intermediate frequency detection circuit, 45...Synchronization signal detection circuit.

Claims (1)

[Scope of Claims] 1. An electronically tuned tuner including a voltage-controlled local oscillator, a voltage sweep circuit that sweeps a control voltage of the voltage-controlled local oscillator of the tuner, and a voltage sweep circuit that receives the output of the electronically tuned tuner and that controls the voltage at the time of tuning. In a sweep tuning type tuning device comprising a sweep stop circuit that stops the voltage sweep of the voltage sweep circuit and an AFC voltage generation circuit, the voltage sweep circuit adjusts the AFC voltage of the AFC voltage generation circuit to a first predetermined value during tuned voltage sweep. circuit means 43 for setting a value, voltage determination means coupled to the circuit means for determining the magnitude of the AFC voltage of the circuit means; It consists of a switch means for turning OFF, and a tuning voltage output circuit coupled to the switch means and including a capacitor for charging and discharging the control voltage, and the voltage determining means is coupled to the circuit means, and when the sweep is stopped, the AFC voltage generation circuit
a first means for determining whether the AFC voltage is higher or lower than a second predetermined value and outputting a binary value of the determination result;
a second predetermined value that is smaller than a predetermined value of , and outputs a binary value of the determination result;
Turns ON and OFF when it is determined that the outputs of the means and the first and second means are both high, and when it is determined that the outputs of both the first and second means are low.
The capacitor is turned OFF and ON to discharge or charge the charge in the capacitor, and when it is determined that the outputs of the first and second means are low and high, respectively, the capacitor is turned OFF and the charging and discharging of the capacitor is stopped. The first and second switching circuits maintain the tuning voltage.
A tuning voltage output circuit that includes a transistor and retains its tuning voltage even if there is no broadcast wave after the sweep is stopped. 2. The tuning voltage output circuit according to claim 1, wherein the third and fourth switching transistors are field effect transistors. 3. The tuning voltage output circuit according to claim 1, wherein the tuning voltage output circuit further includes a switching transistor coupled to the capacitor and dropping the tuning voltage to OV when selecting a channel. .