JPS602648Y2 - oscillation circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to an oscillation circuit used in communication equipment such as radio receivers, and the operation of the oscillation circuit is controlled by inserting a resistor into the collector circuit of the oscillation circuit equipped with a feedback circuit using a differential amplifier. This is to ensure stable and reliable operation.

A commonly used oscillation circuit equipped with a feedback circuit using a differential amplifier is constructed as shown in FIG.

In Figure 1, suppose that switch S is turned on after connecting a positive power source to terminal 1 and a negative power source to terminal 2. At the moment when switch S1 is turned on, transistor Q2
When the transistor Q1 is turned off and the transistor Q1 is turned on, no current flows through the transistor Q2, so the collector voltage is high, and this voltage is applied to the base of the transistor Q1 via the resistor R□.

Therefore, the bias of transistor Q1 becomes deeper, the emitter current flows, the voltage across the emitter resistor R2 increases, and therefore the bias of transistor Q1 becomes shallower.
It turns off.

Then, the current in transistor Q1 stops flowing and the voltage across emitter resistor R2 drops, so transistor Q2
The bias becomes deeper and transistor Q2 is turned on.

Transistor Q□ like this? Q2 performs an oscillation operation by repeatedly turning ON and OFF.

The oscillation frequency of this repetition becomes 1=21 when the switch S2 is connected to the fixed terminal a, and becomes 1=2 when the switch S2 is connected to the fixed terminal a. becomes.

In FIG. 1, the coil L1 consists of a resonant circuit consisting of a coil L2, a capacitor C2 or C3, and a transistor Q1. Q2
The capacitor C1 is a bypass capacitor.

In this way, the conventional oscillation circuit shown in FIG. 1 performs sufficient oscillation operation, but the transistor Q□? If Q2 had exactly the same characteristics, the oscillation would become extremely unstable,
In particular, when switch S2 is switched from fixed terminal a to b during oscillation, the oscillation may stop, and the oscillation will not start unless switch S1 is turned on and off again, which is extremely inconvenient. be.

The present invention eliminates the above-mentioned drawbacks of the conventional circuit by inserting a resistor R3 in the collector circuit of the oscillating transistor Q2 in an oscillator circuit equipped with a feedback circuit using a differential amplifier, as shown in FIG. be.

The oscillation circuit of the present invention will be described below with reference to drawings of one embodiment.

In FIG. 2, it is assumed that a positive power source is connected to terminal 1, a negative power source is connected to terminal 2, and then switch S1 is turned on.

When the switch S□ is turned on, a current tries to flow through the transistors Q9 and Q2 at the same time, but since the resistor R3 is connected to the collector of the transistor Q2, the bias of the transistor Q1 becomes shallow due to the voltage drop, and the The transistor Q□ is turned off and the transistor Q2 is turned on, and the operation starts from this state.

Since the emitter current flows through the transistor Q2, the voltage across the emitter resistor R2 increases, so that the bias of the transistor Q2 becomes shallower, the transistor Q2 is turned off, and no current flows through the transistor Q2.

Then, the collector voltage of transistor Q2 increases,
This is applied to the base of transistor Q1 via resistor R□.

As a result, the bias of transistor Q□ becomes deeper, emitter current flows, and the voltage across emitter resistor R2 rises.
The bias of transistor Q□ becomes shallow and transistor Q1 is turned off.

In this way, the transistor Q□tQ2 performs an oscillation operation by repeatedly turning on and off.

The oscillation frequency of this repetition is as follows when the switch S2 is connected to the fixed terminal a, and when the switch S2 is connected to the fixed terminal a.

Coil L1 is connected to coil L2 and capacitor C2 or C3.
The capacitor C1 is a bypass capacitor.

The value of the resistor R3 is set so that the value of the voltage drop due to the collector current of the transistor Q2 is within the range since oscillation will not occur if the value exceeds the voltage between the base and emitter of the transistor Q□9Q2. .

As described above, according to the present invention, a feedback resistor is inserted between the collector of the oscillation transistor and the base of the feedback transistor, and a coil is provided as a load for coupling with the resonant circuit at the collector of the oscillation transistor. In an oscillation circuit using an amplifier, a resistor is connected in series with the coupling coil so that the voltage drop is smaller than the voltage between the base and emitter of the oscillation and feedback transistors, so that the AC operation and DC operation can be achieved. The synergistic effect with the feedback resistor ensures the on/off operation of the transistors constituting the differential amplifier, allowing smooth start of oscillation and more stable oscillation operation. .

Furthermore, even if the resonant circuit that determines the oscillation frequency is switched, oscillation will never stop, and stable oscillation operation can always be performed reliably.

According to the present invention, the structure can be constructed simply by adding a resistance, which is extremely advantageous economically.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram of a conventional oscillation circuit, and FIG. 2 is an electrical connection diagram of an embodiment of the oscillation circuit of the present invention. 1.2... Power supply terminal, Qo... Feedback transistor, Q2... Oscillation transistor,
R□~R3...Resistor, C...Bypass capacitor, I-'i, L2...Coil, C2
, C3... Capacitor.

Claims (1)

[Scope of utility model registration request] An oscillation circuit using a differential amplifier, in which a collector of an oscillation transistor is connected to a base of a feedback transistor via a feedback resistor, and a coil is provided at the collector of the oscillation transistor as a load for coupling with a resonant circuit. , an oscillation circuit comprising a resistor connected in series with the coupling coil so that the voltage drop is smaller than the voltage between the base and emitter of the oscillation and feedback transistors.