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2. Basic Oscillation Circuits

Generally, basic oscillation circuits can be grouped into

the following 3 categories.

① Use of positive feedback

② Use of negative resistance element

③ Use of delay in transfer time or phase

In the case of ceramic resonators, quartz crystal

oscillators, and LC oscillators, positive feedback is the

circuit of choice.

Among the positive feedback oscillation circuit using an

LC, the tuning type anti-coupling oscillation circuit,

Colpitts and Hartley circuits are typically used.

See Fig. 2-6.

In Fig. 2-6, a transistor, which is the most basic

amplifier, is used.

The oscillation frequencies are approximately the same

as the resonance frequency of the circuit consisting of L,

represented by the following formulas. (Refer to Note 3

on page 11.)

In an LC network, the inductor is replaced by a ceramic

resonator, taking advantage of the fact that the

resonator becomes inductive between resonant and anti-

resonant frequencies.

This is most commonly used in the Colpitts circuit.

The operating principle of these oscillation circuits can

be seen in Fig. 2-7. Oscillation occurs when the

following conditions are satisfied.

Phase Amount

(2-6)

feedback circuit. The operation with a ceramic resonator

can be considered the same.

L

C

fosc. =

(Hartley Circuit)

1

fosc. =

(Colpitts Circuit)

1

(2-4)

(2-5)

Fig. 2-6 Basic Configuration of LC Oscillation Circuit

Amplifier

1

Feedback Circuit

Feedback Ratio :

Fig. 2-7 Principle of Oscillation

Colpitts Circuit

Hartley Circuit

Oscillation Conditions

Loop Gain G=

α·β ≧ 1

Phase Shift

P17E.pdf

2012.10.31