A 0.35 μm CMOS mixed controlled crystal oscillator with low phase noise and wide tuning range

This paper presents a high-performance mixed controlled crystal oscillator. The digital-controlled part is based on a Pierce topology with switched-capacitor bank. Wide tuning range and high linearity are simultaneously achieved by combining discrete capacitors and a continuous voltage tuning varactor. The pull ability is around 99 ppm output frequency variation range. For noise reduction, the supply voltage of the mixed controlled crystal oscillator is regulated at 2.5 V by using on-chip low-drop regulators. The measured phase noise is −145 dBc/Hz at 1 kHz offset frequency by using a 40 MHz fundamental AT–cut crystal. The chip area is 3.6 mm2 for a 0.35 μm standard CMOS process with 3.3 V supply voltage and the power dissipation is 7 mW.