A 2.4GHz to 3.86GHz digitally controlled oscillator with 18.5kHz frequency resolution using single PMOS varactor

A novel varactor using single PMOS is proposed. By utilizing the capacitance difference between saturation and linear region, the proposed varactor can improve frequency resolution of a LC-tank based digitally controlled oscillator without introducing extra fixed loading capacitance. A digitally controlled oscillator with the proposed varactor is designed using 0.13μm CMOS technology for verification. Measurement results show that the minimum frequency resolution is achieved around 18.5 kHz in a frequency range of 2.4GHz to 3.86GHz, indicating the minimum achievable capacitance step of 30 aF. The measured phase noise is −120.6 dBc/Hz at 1MHz offset for 3.05GHz carrier. The power consumption is 2.9mW.