Crystal Oscillator with an Adaptive Conduction Angle for Flicker Noise Reduction

This paper presents a crystal oscillator (XO) design incorporating an adaptive conduction angle (ACA) technique to mitigate flicker noise, a dominant source of phase noise at low offset frequencies. By leveraging an adaptive bias control circuit and gear-shifting control, the conduction angle of the oscillator is dynamically adjusted, reducing the exposure of active devices to non-linear operating regions and thereby minimizing flicker noise up-conversion. The circuit simulations, implemented in TSMC 28-nm HPC+ CMOS, demonstrate that the proposed technique reduces phase noise from -97 dBc/Hz to -109 dBc/Hz at 100 Hz offset and achieves a 5 dB figure-of-merit (FoM) improvement at 10 kHz offset.