A Low-Voltage Robust Class-C VCO with Dual Digital Feedback Loops

This brief presents a low-supply-voltage robust class-C voltage-controlled oscillator (VCO) with the dual digital feedback loops. One is the digital adaptive bias loop (DABL) which is proposed to ensure startup robustness and improve the phase noise performance of the VCO. And the other is the digital amplitude control loop (DACL), which is adopted to stabilize the oscillation amplitude over process, voltage and temperature (PVT) variations. Moreover, a cooperative algorithm is also proposed in order to make the dual digital loops work properly. Besides, the offset canceling comparators are adopted to guarantee the stability of the digital loops. The proposed VCO is implemented in SMIC 0.18 $\mu \text{m}$ CMOS process, achieving a phase noise of −123.3 dBc/Hz at 1 MHz offset from a 2.55 GHz carrier and a 2.2-2.7 GHz frequency tuning range. The figure-of-merit (FoM) is −190.4 dBc/Hz with the total power consumption less than 1.28 mW at the 0.8 V supply voltage.