JPH0326662Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a high-frequency oscillation circuit that is improved so that the oscillation frequency does not change even if the driving voltage changes.

(Prior Art) An example of a conventional high frequency oscillation circuit is shown in FIG.
In FIG. 2, a tuning circuit 1 is connected via a capacitor 2 to the base of a transistor 3 forming a high frequency oscillation circuit. The base of this transistor 3 is connected to the emitter via a capacitor 4, to the collector via a resistor 5, and further to ground via a resistor 6. Also, the emitter is capacitor 7 and resistor 8
The collector is grounded through a large-capacity bypass capacitor 9 and connected to a drive voltage terminal 11 through a resistor 10.

With this configuration, capacitor 4 is provided as a first feedback capacitor, capacitor 7 is provided as a second feedback capacitor, and a high frequency oscillation circuit is formed.

(Problems to be solved by the invention) By the way, in the above-described conventional high frequency oscillation circuit, due to fluctuations in the drive voltage applied to the drive voltage terminal 11, the transistor 3 set by the resistors 10, 5, and 6 The bias voltage at the base of changes,
The value of the collector current of the transistor 3 changes, and the base-emitter capacitance changes. This base
The emitter capacitance is connected in parallel to the tuning capacitance of the tuning circuit 1 along with the capacitors 4 and 7, and their capacitance values are related to the oscillation frequency. Therefore, when the driving voltage increases, the substantial first feedback capacitance consisting of the capacitor 4 and the base-emitter capacitance increases, and the oscillation frequency decreases. Furthermore, when the drive voltage decreases, the oscillation frequency increases. That is, there was a problem in that the oscillation frequency was not stabilized due to fluctuations in the driving voltage.

Furthermore, due to the reduction in driving voltage, transistor 3
There is a problem in that when the degree of amplification of the oscillator decreases, the amount of feedback decreases and oscillation is likely to stop.

The purpose of this invention was to solve the above-mentioned problems of conventional high-frequency oscillation circuits, and to provide a high-frequency oscillation circuit in which the oscillation frequency is stabilized against fluctuations in drive voltage and oscillation stoppage is less likely to occur. It's about doing.

(Means for Solving the Problem) In order to achieve the above object, the high frequency oscillation circuit of the present invention includes a first feedback capacitor provided between the base and emitter of the transistor, and a first feedback capacitor provided between the emitter and collector of the transistor. In the high frequency oscillation circuit, the second feedback capacitor is
It consists of a variable capacitance diode connected so as to be reverse biased by the potential difference between the collector and emitter of the transistor.

(Function) Since the second feedback capacitance provided between the emitter and collector of the transistor is composed of a variable capacitance diode connected so as to be reverse biased by the potential difference between the collector and emitter of the transistor, the drive voltage increases. Even if the capacitance value of the first feedback capacitance between the base and emitter of the transistor becomes large, the potential difference between the collector and emitter becomes large and the reverse bias becomes large. As the capacitance value becomes smaller, changes in the sum of the two feedback capacitances are suppressed to a small value, and fluctuations in the oscillation frequency are corrected. Furthermore, even if the first feedback capacitance becomes smaller due to a decrease in the driving voltage, the second feedback capacitance becomes larger and the fluctuation in the oscillation frequency is corrected.

Furthermore, as the drive voltage decreases, the second feedback capacitance increases and the amount of feedback increases, making it difficult for oscillation to stop.

(Example) Hereinafter, an example of the present invention will be described with reference to FIG. FIG. 1 is a circuit diagram of an embodiment of the high frequency oscillation circuit of the present invention. In FIG. 1, circuit elements that are the same as those in FIG. 2 are given the same reference numerals and redundant explanations will be omitted.

The differences between Figure 1 and Figure 2 are as follows:
In place of the capacitor 7 in FIG. 2, the transistor 3
A variable capacitance diode 12 is interposed between the collector and the emitter, with the cathode connected to the collector. This variable capacitance diode 12 is reverse biased by the collector-emitter potential difference,
The magnitude of the reverse bias is also changed by fluctuations in the drive voltage applied to the drive voltage terminal 11, and as the drive voltage increases, the capacitance value decreases, and as it decreases, it increases.

In such a configuration, when the drive voltage increases,
The bias voltage at the base of transistor 3 increases, the value of the collector current increases, and the base-emitter capacitance increases. However, since the capacitance value of the variable capacitance diode 12 decreases and the amount of change in the sum capacitance value becomes smaller, the decrease in the oscillation frequency is corrected. Moreover, when the driving voltage decreases, the transistor 3
The collector current value of the variable capacitance diode 12 decreases, and the base-emitter capacitance decreases.
Since the capacitance value increases and the amount of change in the sum capacitance value also becomes smaller, the increase in the oscillation frequency is corrected.

Furthermore, transistor 3 due to a decrease in driving voltage
As the amplification degree decreases, not only does the first feedback capacitance actually decrease, but the second feedback capacitance increases, and the ratio of the first and second feedback capacitances changes. As a result, the amount of feedback given to the base of the transistor 3 increases, and the transistor 3 can maintain its oscillation operation without stopping its oscillation even at a lower drive voltage than before.

(Effects of the invention) As explained above, the high-frequency oscillation circuit of the invention has a stable oscillation frequency against fluctuations in drive voltage, and can maintain oscillation without stopping oscillation even at low drive voltages. It has excellent effects.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a high frequency oscillation circuit of the present invention, and FIG. 2 is a circuit diagram of an example of a conventional high frequency oscillation circuit. 3: Transistor, 4: Capacitor, 11: Drive voltage terminal, 12: Variable capacitance diode.

Claims (1)

[Scope of utility model registration request] In a high frequency oscillation circuit including a first feedback capacitor provided between the base and emitter of a transistor, and a second feedback capacitor provided between the collector and emitter of the transistor, the second feedback capacitor is connected to the second feedback capacitor of the transistor. A high-frequency oscillation circuit characterized by comprising a variable capacitance diode connected so as to be reverse biased by a collector-emitter potential difference.