JPH0221708A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To vary the oscillating frequency over a wide frequency range by varying the capacitance of a capacitor being a component of a resonance circuit. CONSTITUTION:The 2nd differential circuit 16 driven based on an output of the 1st differential circuit 11 and a feedback circuit 17 feeding back an output of the 2nd differential circuit 16 to an output terminal of the 1st differential circuit 11 positively are provided to the oscillation circuit and the loop gain of positive feedback by a feedback circuit 17 to less than the unity. When the oscillating frequency is desired to be lower, the gain to maintain the oscillating condition is ensured by sufficiently compensating the reduction if the feedback quantity due to the increase in the capacitance of the capacitor being the component of the resonance circuit 15. In the case of desiring to increase the oscillating frequency, the inductance of a coil being the component of the resonance circuit is selected in advance to be smaller, then it is not required to reduce the capacitance of the capacitor extremely thereby maintaining the oscillating condition. Thus, the oscillating frequency is made variable over a wide frequency range by having only to vary the capacitance of the capacitor being the component of the resonance circuit 15.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an oscillation circuit that oscillates at the resonant frequency of a resonant circuit, and in particular, by changing the capacitance of a capacitor that constitutes the resonant circuit. , relates to a device in which the oscillation frequency can be varied over a wide range.

(Prior Art) As is well known, an oscillation circuit whose oscillation frequency can be varied by changing the resonant frequency of a resonant circuit is constructed as shown in FIG. 1. Q1 in the diagram. Q2 is an NPN transistor that constitutes the differential amplifier 11.

The emitters of transistors Ql and Q2 are commonly connected,
The connection point is grounded via a constant current source 11.

The collectors of transistors QL and Q2 are respectively connected to output terminals 12. ta, and resistors RL and R
2, then the constant voltage source E1 with the polarity shown
grounded via. The bases of the transistors Ql and Q2 are connected in common through resistors R3 and R4, respectively, and then grounded through a constant voltage source E2 with the polarity shown. The base of transistor Q2 is grounded via capacitor C1.

Between the base of the transistor Q1 and the output terminal 13,
Capacitors C2 and C3 are connected in series to form a differential amplifier 1.
A feedback path 14 is configured to feed back the output of 1 to the input side.

A connection point between capacitors C2 and C3 is grounded via a resonant circuit 15 in which a capacitor C4 and a coil L are connected in parallel.

In the above-mentioned oscillation circuit, the feedback path (4) performs a positive feedback action only at the resonant frequency of the resonant circuit 15, and as a result, it oscillates at the resonant frequency. In order to change the oscillation frequency, one or both of the capacitance of the capacitor C4 and the inductance of the coil L are changed, and the resonant circuit 1
All you have to do is change the resonance frequency of 5. - For boat fishing, the oscillation frequency is changed by changing only the capacitance of the capacitor C4.

However, in the conventional oscillation circuit, the transistor Ql
, Q2, when changing the oscillation frequency over a wide frequency range from a high frequency approaching the operating limit to a low frequency, the following problem occurs.

First, in order to oscillate at a high frequency, it is necessary to reduce the capacitance of capacitor C4, but if it is made too small, its impedance and transistor Ql,
The feedback signal is reduced depending on the ratio to the impedance due to the parasitic capacitance of Q2, and oscillation is stopped. In order to oscillate up to a high frequency, it is necessary to set the capacitance of the capacitor C4 to a sufficiently small value in advance.

However, if the capacitance of the capacitor C4 is set to be sufficiently small in advance, it is necessary to change the capacitance of the capacitor C4 to a considerably large value when lowering the oscillation frequency. In this way, the resonant circuit 15
has a very low impedance for the low frequency at which it is intended to oscillate, and the amount of feedback also decreases, stopping oscillation.

(Problem to be Solved by the Invention) As mentioned above, in conventional oscillation circuits, it is extremely difficult to change the oscillation frequency over a wide frequency range simply by changing the capacitance of the capacitor that makes up the resonant circuit. .

Therefore, the present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an oscillation circuit that can vary the oscillation frequency over a wide frequency range by simply changing the capacitance of the capacitor that constitutes the resonant circuit.

[Structure of the Invention] (Means for Solving the Problems) The present invention includes a first differential circuit, a feedback path that returns the output of the first differential circuit to the input side, and a resonance circuit in the feedback path. The object is a device that is equipped with a resonant circuit that performs a positive feedback action at a frequency, and that performs an oscillation operation at the resonant frequency of the resonant circuit. and a second differential circuit driven based on the output of the first differential circuit, and a feedback circuit that positively feeds back the output of the second differential circuit to the output terminal of the first differential circuit. The positive feedback loop gain of the feedback circuit is set to less than 1.

(Function) According to the above configuration, when it is desired to lower the oscillation frequency, it is possible to secure a gain that can sufficiently compensate for the decrease in feedback amount due to increasing the capacitance of the capacitor forming the resonant circuit and maintain the oscillation condition. When it is desired to increase the oscillation frequency, by setting the inductance of the coil constituting the resonant circuit small in advance, it is not necessary to make the capacitance of the capacitor extremely small, and the oscillation condition can be maintained. As a result, the oscillation frequency can be varied over a wide frequency range simply by changing the capacitance of the capacitor that constitutes the resonant circuit.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 3 are indicated with the same symbols. The collectors of the transistors Ql and Q2 are connected to NPN transistors Q3 . Each is connected to the base of Q4. The emitters of transistors Q3 and Q4 are connected to resistors R5 and R5, respectively.
After being connected in common through Re, they are grounded through a constant current source I2.

Transistor Q3. Each collector of Q4 is connected to an NPN transistor Q5 . After being connected to the base of Q6 and commonly connected via resistors R7 and R8,
connected to. Transistor Q5. Each emitter of QB is connected to a resistor R2°R1, and each collector is connected to a constant voltage source El.

The differential amplifier 16 is driven based on the output of the differential amplifier 11, and the output is positively fed back to the output terminal of the differential amplifier 11 via the feedback circuit 17. The loop gain T of this positive feedback is the value of the resistor R5, Re.

If the values of resistors R7 and R8 are RL, and the mutual conductance of transistors Q3 and Q4 is gll, then T-RL/
(RE + (1,/gm) 1.

If this loop gain T is set to 1 or less, that is, T<1, the gain of the differential amplifier 11 that constitutes the oscillation circuit will equivalently be 1/(1-T) times (>1), By increasing only the capacitance of the capacitor C4 of the resonant circuit 15 by that amount, the decrease in the amount of feedback when the oscillation frequency is lowered can be compensated for.

Furthermore, if the inductance of the coil L constituting the resonance circuit 15 is set small in advance, even when it is desired to increase the oscillation frequency, there is no need to extremely reduce the capacitance of the capacitor C4, and the oscillation conditions can be maintained. Therefore, as a result, the capacitor C4 constituting the resonant circuit 15
By simply changing the capacitance of the oscillation frequency, the oscillation frequency can be varied over a wide frequency range.

FIG. 2 shows another embodiment of the invention.

The same parts as in FIG. 1 are given the same symbols, and the transistor Q1. Each collector of Q2 is connected to an NPN type transistor Q7. Each is connected to the base of Q8. Transistor Q7. Q8 has its respective collectors both connected to the constant voltage source El, and each emitter connected to the transistor Q3. Q
4, and a constant current source I8. I4
grounded via.

Transistor Q7. Q8 constitutes an emitter follower, and the differential amplifier 11 stabilizes the oscillation frequency under the influence of load fluctuations in the subsequent stage.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide an oscillation circuit whose oscillation frequency can be varied over a wide frequency range simply by changing the capacitance of the capacitor that constitutes the resonant circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a circuit diagram showing another embodiment of the invention, and FIG. 3 is a circuit diagram showing a conventional oscillation circuit. 11...Differential amplifier, 12.13...Output terminal, 1
4... Feedback path, 15... Resonant circuit, 1B... Differential amplifier, 17... Feedback circuit. Figure 1 Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] A first differential circuit, a feedback path that returns the output of the first differential circuit to the input side, and a resonant circuit that causes the feedback path to perform a positive feedback action at a resonant frequency. In an oscillation circuit that performs an oscillation operation at a resonant frequency, a second differential circuit is driven based on the output of the first differential circuit, and an output of the second differential circuit is driven by the first differential circuit. An oscillation circuit comprising: a feedback circuit that provides positive feedback to an output end of the circuit, and a loop gain of the positive feedback provided by the feedback circuit is set to less than 1.