JPH0149208B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides a tuning circuit equipped with a variable capacitance diode, which eliminates waveform distortion and tuning point fluctuations caused by saturation of the variable capacitance diode that occurs when a signal with a strong electric field strength is input. The present invention relates to a protection circuit configured to provide stable operation of the circuit.

In general, there are two types of tuning circuits: a C variable type tuning circuit in which a variable capacitance diode is used exclusively as a variable element, and an L variable type tuning circuit in which a variable inductance is used exclusively as a variable element and a variable capacitance diode is provided for tracking adjustment. However, in a tuning circuit equipped with a variable capacitance diode, especially an antenna tuning circuit, when a signal with a strong electric field strength is input from the outside and a strong voltage exceeding the bias voltage is applied to the variable capacitance diode,
There is a risk that the variable capacitance diode may become saturated and the output signal waveform may be distorted or the tuning point may fluctuate, resulting in a drawback that stable operation of the tuning circuit cannot be obtained.

Therefore, this application aims to prevent the variable capacitance diode from being saturated when an input signal with strong electric field strength arrives in a tuning circuit, especially an antenna tuning circuit.
By suppressing the input signal using a push-pull circuit controlled by the AGC voltage, it protects the variable capacitance diode from strong input signals and provides stable operation of the tuned circuit. An example is detailed below regarding the drawing.
The antenna circuit consists of input coil 1 as shown in Figure 1.
, a tuning coil 2, a transmission coil 3, and a suppression coil 4, each coil being wound around the same bobbin 5 and inductively coupled to each other as shown in FIG. The input coil 1 is connected to an antenna 6, and the tuning coil 2 is connected to a variable voltage circuit 7.
A tuning variable capacitance diode 8 that is variably adjusted by the transmission coil 3 is connected to the bases of a pair of transistors 9a and 9b that are push-pull connected to both ends of the transmission coil 3, and to both ends of the suppression coil 4. The collectors of the pair of transistors 9a and 9b are connected to each other, and the input coil 1 and the suppression coil 4 are in an opposite phase relationship. Further, the B power supply is applied to the middle point of the transmission coil 3, and the emitters of the transistors 9a and 9b are applied with a voltage of 0 to 1.2 V, for example, to the base as the input signal increases.
The collectors of the control transistors 10 to which an AGC voltage that changes to the voltage is applied and whose emitters are grounded are commonly connected. Further, the transmission coil 3
A pair of transistors 11a and 12a are connected at both ends of the
Transistors 11b and 12b are differentially connected to each other, and an induction coil 1 is connected between their emitters.
An output amplifier circuit 15 is connected to the collector of a transistor 14 which is biased by an AGC voltage which changes from 1.2V to 0V as the input signal increases, for example, as the input signal increases. 1
Reference numeral 6 designates a next-stage high-frequency amplification circuit consisting of a tuning circuit in which a variable capacitance diode 19 for tuning that is variably adjusted by a variable voltage circuit 18 is connected to a primary coil 17, and a secondary coil 20 inductively coupled to the tuning circuit. .

Therefore, when the input signal arriving at the antenna 6 is weak, it is applied to the base of the transistor 10.
Since the AGC voltage is low, the transistor is inactive, and the pair of transistors 9a, 9b whose collectors and emitters are connected are also kept inactive. Therefore, in this state, the input signal is transmitted from the antenna coil 1 to the tuning coil 2 and the transmission coil 3 without being attenuated in any way, and the output signal from the transmission coil 3 is input to the output amplifier circuit 15 and is amplified. The output is applied to the next stage high frequency amplification circuit 16. On the other hand, antenna 6
When a strong input signal arrives at , the AGC voltage also increases, the base potential of the transistor 10 rises, and the transistor 10 enters the operating state, and a pair of push-pull connected transistors 9
a and 9b are also activated, and their outputs are negatively fed back to the suppression coil 4 in opposite phase to the input signal. Therefore, the input signal from the antenna 6 is suppressed by the signal negatively fed back to the suppression coil 4, and the signals induced in the tuning coil 2 and the transmission coil 3 are attenuated.
The degree of attenuation increases as the electric field strength of the input signal becomes stronger. Therefore, the variable capacitance diode connected to the tuning circuit is protected from the strong input signal, and stable operation of the tuning circuit is obtained.

Note that in the above, the pair of transistors 9a,
The collector of the transistor 10 may be connected to the base of the transistor 9b, and the emitters of the transistors 9a and 9b may be grounded. In this case as well, when the input signal voltage exceeds a certain value, the pair is connected via the transistor 10. transistors 9a and 9b operate,
The higher the base-emitter potential difference, that is, the higher the electric field strength of the input signal, the more the input signal is suppressed.

FIG. 3 shows the configuration shown in FIG. 1, in which a tuning signal from a tuning circuit consisting of a tuning coil 2 and a variable capacitance diode 8 is output to the next stage circuit via an FET 23, and an inductive primary coil is connected to the source of the FET 23. 24a is connected to the inductive secondary coil 24a, and both ends of the inductive secondary coil 24b inductively coupled to the inductive secondary coil 24b are respectively connected to the bases of a pair of push-pull connected transistors 9a and 9b. This is the same as the configuration shown in FIG.

FIG. 4 shows the configuration shown in FIG. 1 described above.
A pair of transistors 9a and 9b share the suppression coil 4 and the tuning coil 2 and are push-pull connected.
FIG. 5 shows another embodiment in which the input signal is suppressed by negative feedback of the output of the tuning coil 2 to the tuning coil 2, and FIG. Another embodiment in which the tuning coil 2 is omitted by connecting a variable capacitance diode 8 variable by the circuit 7 to form a tuning circuit, and the gate of the FET 23 is connected to the tuning circuit, FIG. 6 shows a tuning circuit in which a variable capacitance diode 8, which is varied by a variable voltage circuit 7, is connected to an input coil 1 connected to an antenna 6, and a tuning signal from this tuning circuit is directly guided to the next stage circuit. At the same time, an induction coil 3' and a suppression coil 4 are provided which are inductively coupled to the input coil 1, and both ends of the induction coil 3' are connected to the bases of a pair of transistors 9a and 9b which are push-pull connected to output the output. Another example in which negative feedback is provided to the suppression coil 4, and FIG. 7 shows a case in which the input coil 1 is omitted from the above-mentioned FIG. 4 and the drain of the FET 26 connected to the antenna 6 is connected to the tuning coil 2. Other embodiments are shown, and their functions are similar to those of the configuration shown in FIG.
In the figure, E indicates the tuning voltage.

In addition, although the above-mentioned embodiments all show a C variable type tuning circuit, that is, an electronic tuning circuit, in which a variable capacitance diode is used as a variable tuning element, FIGS. 8 and 9 show an L variable type tuning circuit in which a variable inductance is used as a variable tuning element. In FIG. 8, a variable inductance element 27 has an antenna 6 on its primary side and a tuning capacitor 28 on its secondary side.
In addition to this, a variable capacitance diode 30 for tracking adjustment that is varied by a variable voltage circuit 29 is connected, and the gate of an FET 31 is connected to the tuning circuit. The source of this FET 31 is connected to a transmission coil 32, and the bases of a pair of transistors 9a and 9b which are push-pull connected to both ends of an output coil 33 which is inductively coupled to this coil 32 are respectively connected to a next-stage amplifier circuit 34. There is.
The emitters of the pair of transistors 9a and 9b are connected to the collector of a control transistor 35 whose base voltage is the AGC voltage that changes from 0 to 1.2V as the input voltage increases, and the collector of the control transistor 35 is connected to the emitter of the output coil 33. For example, as the input voltage increases,
The collectors of transistors 36 whose base voltages are AGC voltages varying from 1.2 to 0V are connected to each other. Further, an induction coil 3 provided in the tuned circuit is connected to the collector of the pair of transistors 9a and 9b.
A suppression coil 38 is connected which is inductively coupled to 7 in an opposite phase.

However, when the electric field strength of the input signal from the antenna 6 is weak, the base potential of the pair of push-pull connected transistors 9a and 9b is low and the emitter potential is high.
a, 9b are placed in a non-operating state. On the other hand, when the electric field strength of the input signal from the antenna 6 becomes strong and the base potential of the pair of transistors 9a and 9b becomes high and the emitter potential thereof becomes low, the transistors 9a and 9b become in an operating state, and the signal obtained from their collectors becomes active. The signal is negatively fed back to the suppression coil 38, and the input signal is suppressed via the induction coil 37 which is inductively coupled to the suppression coil 38, and the signal transmission characteristic of the output amplifier circuit 34 is attenuated. The degree of attenuation corresponds to the potential difference between the base and emitter of the transistors 9a and 9b, and the greater the potential difference, the greater the attenuation, thereby protecting the variable capacitance diode 30 from strong input signals.

Further, FIG. 9 shows an input signal from an antenna 6 connecting the primary side of a variable inductance element 27 and a variable capacitance diode 30 for tracking adjustment, which is varied by a variable voltage circuit 29, to the next stage circuit via an FET 41. and applying a part of the input signal to the bases of the push-pull circuit transistors 9a and 9b via the inductive coupling circuit 42,
Another embodiment is shown in which the signal between the collectors is negatively fed back to the secondary side of the variable inductance element 27 to suppress the input signal, and 39 in the figure shows a voltage of 1.2 V as the input signal increases. A control transistor whose base voltage is the AGC voltage that changes from ~0V and whose emitter potential is used as the base of the pair of transistors 9a and 9b; 40 is an AGC voltage that changes from, for example, 0V to 1.2V as the input signal increases; This is a control transistor which uses the base voltage as the base voltage and the collector potential as the emitter potential of the transistors 9a and 9b.

and transistor 9a of the push-pull circuit,
9b is controlled by transistors 39 and 40 whose base potential is the AGC voltage, and thereby the input signal is suppressed when there is a strong electric field, as described above.

Note that although the embodiment is shown using a disparate transistor, it goes without saying that an FET may also be used.

In addition, not only the wiring diagram of the embodiment but also many feedback circuits can be implemented via push-pull circuits as will be understood from this description.

As described above, according to the present application, since the input signal is suppressed according to the strength of the input signal, the variable capacitance diode is protected from strong input signals, and stable operation of the tuned circuit can be expected. Suppression is performed using a push-pull circuit, so there is no risk of waveform distortion;
Since the configuration is controlled by the AGC voltage, it has the advantage of being able to adequately respond to large changes in electric field strength.

[Brief explanation of drawings]

The drawings show embodiments of the present application; Fig. 1 is an electric circuit diagram, Fig. 2 is a plan view of a bobbin around which each coil is wound, and Figs. 3 to 9 show other embodiments of the present application. It is an electrical circuit diagram. In the figure, 1 is an input coil, 2 is a tuning coil, 3 is a transmission coil, 4 is a suppression coil, 8, 30 are variable capacitance diodes, 9a, 9b, 10 are transistors,
15 and 34 are output amplifier circuits, 16 is a high frequency amplifier circuit, and 27 is a variable inductance element.

Claims (1)

[Claims] 1. In a tuned circuit equipped with a variable capacitance diode, the output signal of the tuned circuit is fed back through a push-pull circuit controlled by an AGC voltage so as to have an opposite phase to the input signal. A protection circuit characterized by: 2. A protection circuit in a tuned circuit according to claim 1, wherein the tuned circuit is an electronic tuned circuit. 3. A protection circuit in a tuned circuit according to claim 1, wherein the tuned circuit is a variable inductance circuit equipped with a variable capacitance diode for tracking adjustment. 4. A protection circuit in a tuning circuit according to claim 1, 2 or 3, wherein the tuning circuit is an antenna tuning circuit. 5. As the input signal increases between the bases of a pair of transistors forming a push-pull circuit, the potential difference between the base and emitter increases.
Claims 1, 2, 3, or 4, wherein an AGC voltage is applied and an output signal is fed back from the collectors of the pair of transistors.
Protection circuit in the tuned circuit described in section. 6 Between the emitters of a pair of transistors forming a push-pull circuit, as the input signal increases, the potential difference between the base and emitter increases.
Claims 1, 2, 3, or 4, wherein an AGC voltage is applied and an output signal is fed back from the collectors of the pair of transistors.
Protection circuit in the tuned circuit described in section.