Unregulated quartz crystal oscillator circuit without inductor L

Unregulated quartz crystal oscillator circuit without inductor L

Function of the circuit

If an LC resonant circuit is used as the collector load of the transistor, the oscillation frequency of the Pierce CB or Boers BE circuit must be slightly adjusted to stabilize the oscillation. If the inductor L is not used, an unregulated oscillation circuit such as this circuit can be used.

How the Circuit Works

If the quartz oscillator is regarded as an inductor L, it can be treated as a deformed Clapp oscillator circuit. Capacitors C2 and C3 perform positive feedback. The lower the frequency, the larger the capacitance. When the capacitance is 100PF, the oscillation frequency can reach 5~20MHZ. The most appropriate capacitance should be selected according to the use requirements.

C1 and VC1 are used to fine-tune the oscillation frequency. If a varactor diode is connected here, it becomes a VCXO circuit. The frequency will also change to a certain extent when the load of the oscillation circuit changes, so a buffer amplifier TR2 should be added between the load and the output. The base resistor R6 and the emitter resistor R3 are stable resistors that ensure that the emitter follower does not produce abnormal oscillation.

If the load resistance is 50 ohms, the bias resistor R3 of TT2 needs to be adjusted to reduce waveform distortion.