JPH0119466Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tuning device, and particularly to a tuning device that uses a so-called electronic tuning tuner, and whose reception frequency is limited.

In tuning devices such as television receivers, radio receivers, and communication wireless receivers, the frequency bands that can be received may be regulated by the Radio Law. In such cases, conventionally, the frequency band has been limited so that the tuning voltage applied to the electronic tuner does not fall below a certain value or exceed a certain value.

FIG. 1 is a circuit diagram showing a conventional tuning device in which the lower frequencies of the receiving band are limited.

In the figure, the output voltage of a variable voltage source 10 is applied to a tuner 8 via a resistor 9 as a tuning voltage. This tuner 8 is a so-called electronically tuned tuner whose reception frequency changes depending on the applied tuning voltage. Note that the resistor 9 is the output impedance of the variable voltage source 10. On the other hand, a predetermined voltage is applied to the power supply terminal 3 from a power supply (not shown). This power terminal 3
The voltage applied to is divided by a voltage dividing circuit configured by a fixed resistor 4 and a voltage adjusting variable resistor 5 connected in series. The divided voltage output of this voltage dividing circuit, that is, the voltage output from the connection point between the resistor 4 and the variable resistor 5 is applied to the aforementioned tuner 8 via the anode-cathode of the diode 6 and the protective resistor 7. Superimposed on the tuning voltage.
Note that the connection point between the resistor 4 and the variable resistor 5 is connected to the collector of the transistor 2. A band switching signal is applied to the base of the transistor 2 via a band switching signal application terminal 1. This band switching signal is a signal that is at a low level when the band being received is a band that requires lower frequency restriction, and is at a high level when other bands are being received. The emitter of transistor 2 is grounded.

In operation, if it is necessary to limit the lower reception frequencies of the band being received, the band switching signal is brought to a low level. Therefore, transistor 2 is in a non-conducting state. Here, the output voltage of the variable voltage source 10 is connected to the resistor 4 and the variable resistor 5.
If the potential is higher than the potential at the connection point, the diode 6 is turned off, so that the output voltage of the variable voltage source 10 is directly applied to the tuner 8. In order to lower the tuning frequency of tuner 8, variable voltage source 1
When the output voltage is lowered by adjusting 0 and the output voltage becomes lower than the potential at the connection point between the resistor 4 and the variable resistor 5, the diode 6 is turned on.
Therefore, the output voltage of the voltage dividing circuit constituted by the resistor 4 and the variable resistor 5 is superimposed on the tuning voltage applied to the tuner 8. Therefore,
The tuning voltage will never be lower than the output voltage of the voltage divider circuit. This limits the lower frequencies of the reception band.

Next, when there is no need to limit the lower receiving frequency of the receiving band, the band switching signal is set to a high level and the transistor 2 becomes conductive. Therefore, the connection point between the resistor 4 and the variable resistor 5 is grounded, and its divided voltage output becomes 0 potential. Therefore, no matter how much the output voltage of the variable voltage source decreases, the diode 6 will not turn on, and no voltage will be superimposed on the tuning voltage. Therefore, the lower frequencies of the band are not limited.

By the way, in the above-mentioned device, since fluctuations in the voltage drop across the diode 6 due to temperature changes affect the tuning voltage, the tuner 8 may receive signals outside the desired reception band or may not be able to receive signals in the desired reception band. It had some drawbacks, such as being easily lost. In particular, when a tuner in which the reception frequency changes sharply with respect to the tuning voltage is used, this drawback becomes conspicuous.

In the above description, the drawbacks of the tuning device in which the frequencies on the lower side of the receiving band are limited have been explained, but the same drawbacks also exist in the tuning device in which the frequencies on the upper side of the receiving band are limited.

Therefore, the main objective of this invention is to provide a tuning device capable of compensating for temperature-induced variations in the voltage superimposed on the tuning voltage to limit the receiving frequency.

In summary, this invention consists of a tuning voltage generating means that generates a tuning voltage, a tuner whose reception frequency changes according to changes in the tuning voltage, and a tuning voltage that is superimposed on the tuning voltage to limit the reception frequency of the tuner. In a tuning device including a receiving frequency limiting voltage generating means for generating a predetermined voltage and a backflow prevention diode inserted between the voltage generating means and the tuner, the receiving frequency limiting voltage generating means and the diode are connected to each other. A common collector type transistor is inserted between the transistors, and the temperature characteristics between the base and emitter of the transistor absorb the temperature characteristics of the diode, thereby preventing the voltage superimposed on the tuning voltage from fluctuating due to temperature changes. It was designed to compensate.

The above objects and other objects and features of the present invention will become more apparent from the following detailed description with reference to the drawings.

FIG. 2 is a circuit diagram showing an embodiment of this invention. Note that this embodiment is an example of a tuning device that limits the reception frequency on the lower side of the reception band.
In terms of configuration, the circuit of FIG. 2 is similar to the circuit of FIG. 1 except for the following points, and corresponding parts are given the same reference numerals and their explanation will be omitted. A feature of the circuit shown in FIG. 2 is that a PNP type transistor 12 is inserted between the connection point between the resistor 4 and the variable resistor 5 and the diode 6. The base of this transistor 12 is connected to a resistor 4 and a variable resistor 5.
connected to the connection point. Also, transistor 1
The emitter 2 is connected to the anode of the diode 6 and is also connected to the power supply terminal 3 via a resistor 11 . Further, the base of the transistor 12 is grounded. That is, the transistor 12 constitutes a collector grounded circuit. Therefore,
Its amplification gain is 1.

Here, the transistor 2 used has a temperature characteristic between its base and emitter that is almost the same as that of the diode 6. That is, the principle of this embodiment is to cancel the temperature characteristics of the diode 6 with the temperature characteristics between the base and emitter of the transistor 12, thereby compensating for variations in the superimposed voltage due to temperature.

In operation, when receiving a band that requires lower frequency restriction, a low-level band switching signal is applied to the band switching signal application terminal 1. Therefore, transistor 2 becomes non-conductive. Therefore, the divided voltage output obtained from the connection point between the resistor 4 and the variable resistor 5 is directly applied to the base of the transistor 12, and its base-emitter voltage is
V _BE is increased by 2 and output from the emitter.
Here, if the output voltage of the variable voltage source 10 is lowered than the voltage at the emitter of the transistor 12,
The voltage output from this emitter is lowered by the voltage drop V _D caused by the diode 6, and then applied to the resistor 7.
The tuning voltage is superimposed on the tuning voltage. If the voltage drop across diode 6 becomes V _E +△V _D due to a change in temperature, then
The output voltage at the emitter of transistor 12 is also V _BE
+△V _BE . As mentioned above, transistor 1
Since the temperature characteristics between the base and emitter of diode 2 are selected to be almost the same as those of diode 6, V _BE
≒V _D , △V _BE ≒△V _D can be set. Therefore, voltage fluctuations due to temperature changes in the diode 6 are canceled by the transistor 12, and a stable superimposed voltage can be supplied against temperature changes.

Next, when receiving a band that does not require lower frequency restriction, a high-level band switching signal is applied to the band switching signal application terminal 1. Therefore, transistor 2 becomes conductive, and the base potential of transistor 12 becomes zero potential. Therefore, the transistor 12 becomes saturated, and the emitter potential of the transistor 12 becomes approximately zero potential.
In this case, no matter how much the output voltage of the variable voltage source 10 decreases, the diode 6 will never turn on, and no voltage will be superimposed on the tuning voltage.

FIG. 3 is a circuit diagram showing another embodiment of this invention. Note that this embodiment shows a tuning device in which the upper frequency of the reception band is limited. In the figure, this embodiment is similar to the embodiment of FIG. 2 except for the following points, and corresponding parts are given the same reference numerals and their explanation will be omitted. In the circuit of FIG. 3, the connection polarity of the diode 6 is reversed from that of the circuit of FIG. That is, in the circuit shown in FIG. 3, when the output voltage of the variable voltage source 10 exceeds a predetermined voltage, the diode 6 becomes conductive, and the tuning voltage does not exceed the predetermined voltage. On the other hand, the voltage applied to the power supply terminal 3 is
Similar to the circuit shown in the figure, the voltage is divided by a variable resistor 5 and a resistor 4. An NPN transistor 13 is connected between the connection point between the variable resistor 5 and the resistor 4 and the cathode of the diode 6.
The base of this transistor 13 is connected to the variable resistor 5
and the connection point between the resistor 4 and the resistor 4. Further, its collector is connected to the power supply terminal 3, and its emitter is grounded via a resistor 11 and connected to the cathode of the diode 6. That is, this transistor 13 also constitutes a common collector circuit like the transistor 12 in FIG. Similarly to the circuit shown in FIG. 2, the circuit shown in FIG. 3 also uses the temperature characteristics between the base and emitter of the transistor 13 to cancel out the temperature characteristics of the diode 6, thereby compensating for temperature fluctuations in the superimposed voltage.

The operation of the circuit shown in FIG. 3 will be easily understood from the operation of the circuit shown in FIG. 2, so a description thereof will be omitted.

As described above, according to this invention, it is possible to obtain a superimposed voltage that is stable against temperature changes, and it is possible to prevent unnecessary signals outside the receiving band from being stably received.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional tuning device, and particularly shows a tuning device in which frequencies on the lower side of the receiving band are limited. FIG. 2 is a circuit diagram of one embodiment of this invention, and particularly shows an example of a tuning device in which the lower frequencies of the receiving band are limited.
FIG. 3 is a circuit diagram showing another embodiment of the present invention, and particularly shows an example of a tuning device in which the upper frequency of the reception band is limited. In the figure, 1 is a band switching signal application terminal, 2
is a switching transistor, 3 is a power supply terminal,
4 is a fixed resistor for voltage division, 5 is a variable resistor for voltage adjustment, 6 is a reverse current blocking diode, 7 is a protection resistor, 8 is a tuner, 9 is the output impedance of variable voltage source 10, 10 is variable voltage source, 11 is an emitter resistor, 12 is a PNP type transistor, and 13 is an emitter resistor.
Shows an NPN type transistor.

Claims (1)

[Claims for Utility Model Registration] (1) A tuning voltage generating means for generating a tuning voltage, a tuner whose receiving frequency changes according to the tuning voltage, and a tuning voltage generating means for limiting the receiving frequency of the tuner. A tuning device comprising: a receiving frequency limiting voltage generating means for generating a predetermined voltage superimposed on the receiving frequency limiting voltage generating means; and a diode inserted between the receiving frequency limiting voltage generating means and the tuner; The transistor includes a transistor that receives the output voltage of the voltage generating means as a base input and whose emitter output is applied to the diode to form a common collector circuit, and the temperature characteristic of the diode is determined by the temperature characteristic between the base and emitter of the transistor. A tuning device characterized by being designed to cancel. (2) The receiving frequency limiting voltage generating means includes means for generating a voltage for limiting the receiving frequency below the receiving band of the tuner, and the anode of the diode is connected to the emitter of the transistor. The tuning device according to claim 1, wherein the transistor has a cathode connected to the tuner, and the polarity of the transistor is selected as PNP type. (3) The receiving frequency limiting voltage generating means includes means for generating a voltage for limiting the upper limit frequency of the receiving band of the tuner, and the diode has a cathode connected to the emitter of the transistor, and the diode has a cathode connected to the emitter of the transistor. The tuning device according to claim 1, wherein an anode is connected to the tuner, and the polarity of the transistor is selected as NPN type.