Quartz crystal sine oscillator

The circuit shown in the figure is a sine wave oscillator composed of a quartz resonant crystal SJT and a gate A of the six-inverter integrated circuit CD4069. Compared with ordinary RC phase-shift oscillators, the frequency stability of crystal oscillators can be as high as 10-5 or higher. This is a high indicator that RC phase-shift oscillators cannot achieve (the frequency stability of RC phase-shift oscillators can only reach the order of 10-2). The CMOS NOT gate and the negative feedback bias resistor Rl form an inverting amplifier circuit. The quartz crystal SJT and Cl and C2 form a 7c type positive feedback branch. The quartz crystal is inductive near its inherent resonant frequency. This inductance and capacitors Cl and C2 form a resonant circuit, forming a frequency-selective phase-shift feedback network that feeds back to the amplifier input to generate oscillation. The oscillation frequency can be fine-tuned by adjusting capacitor C2.

Component selection:

Six inverter integrated circuit A: CD4069. Capacitor Cl: 20pF, C2: 3~22pF, C3: 1000pF. Resistor Rl: 10MΩ. Quartz crystal SJT: 32.768kHz.

Circuit connection method:

The six-inverter integrated circuit CD4069 only uses 1/6 gates. If the remaining gates are not used, the input terminals can be connected to VDD or VSS, and the output terminals can be left floating. Pin 14 (VDD) is connected to the positive power supply, and pin 7 (VSS) is grounded.