A Low-Voltage Design of Digitally-Controlled Oscillator Based on the gm/ID Methodology

A low-voltage digitally-controlled oscillator (DCO) utilized in a medical implant communication service (MICS) frequency band is designed. A DCO core operating in subthreshold region is designed based on the g(m)/I-D methodology for optimization. The oscillation frequency is tuned by digital logic block. Thermometer coder with data-weighted averaging and delta-sigma modulator (DSM) are implemented for frequency tuning. High frequency resolution is achieved by using the DSM. The DCO fabricated in a 130-nm CMOS technology has achieved a phase noise of -115.3 dBc/Hz at 200 kHz offset frequency with tuning range of 382 MHz to 412 MHz for the MICS band. It consumes 840 mu W from a 0.7-V supply voltage and has a high frequency resolution of 18 kHz.