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Date：Dec 02,2022
The Colpitts oscillator circuit, as shown in Figure 4.4-1(a), is usually used for oscillation circuits. In this circuit, capacitors C1 and C2 are used to divide the signal at both ends of the resonator. The input side is connected to C1 and the output side is connected to C2, which can be regarded as a feedback amplifier.
Next, the oscillation state of the crystal oscillator is represented by the resonant circuit with negative capacitance Ri and load capacitance CL, as shown in Figure 4.4-1(b). At this time, the crystal oscillator's equivalent inductance Le and equivalent resistance RL at load when oscillating in the resonator are as follows:
Frequency Condition:
Amplitude Condition: RL ≤ Ri
RL: Equivalent resistance at load; RL = R1(1+C0/CL)2. The amplitude condition in Formula (2) is an important condition for oscillation startup. The negative resistance Ri in the circuit must have a value that is at least 5 times larger than the equivalent resistance RL at load.
RL: Equivalent resistance at load; RL = R1(1+C0/CL)2. The amplitude condition in Formula (2) is an important condition for oscillation startup. The negative resistance Ri in the circuit must have a value that is at least 5 times larger than the equivalent resistance RL at load.
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