A 5.6 GHz LC digitally controlled oscillator with high frequency resolution using novel quadruple resolution varactor

This paper reports a high resolution LC-based digitally controlled oscillator (DCO) using novel quadruple resolution varactor. Proposed DCO has a high frequency resolution and a wide tuning range of 2.2 GHz with a low phase noise at 5.6 GHz. A process and temperature invariant quadruple resolution varactor is proposed to achieve the finest frequency resolution. The proposed varactor achieves one fourth capacitance of a fine varactor, and therefore DCO achieves a very fine frequency resolution with low phase noise. Also, the diode connected circuit makes the proposed varactor robust from the process and temperature variations. The DCO implemented in 0.13 μm CMOS process operates from 3.4 GHz to 5.6 GHz with a resolution from 260 Hz to 0.93 kHz by consuming a power from 5.5 mW to 3.2 mW, respectively. The designed DCO achieves a low phase-noise of −118 dBc/Hz at 1 MHz offset.