A 2.4-GHz LC-Tank VCO with Minimum Supply Pushing Regulation Technique

Design of low drop-out (LDO) supply regulated 2.4 GHz low phase noise LC-tank voltage controlled oscillator (VCO) is presented. Low-frequency supply noise sensitivity of the VCO phase noise is derived, and output noise and power supply rejection (PSR) profile of the LDO is optimized for minimum supply pushing. The LDO PSR and output noise is optimized by shaping the LDO AC response and tuning the equivalent-series resistance (ESR) of the bypass capacitor, while achieving maximum LDO current efficiency. To verify the results, two 2.4 GHz LC-tank VCOs, with a PMOS and an NMOS switching pair respectively with associated PMOS supply regulators are designed and fabricated in a 0.18 mum, 7-layer metal CMOS process. The implemented VCOs achieve less than 95 dBc/Hz phase noise at 100 kHz offset with a current consumption of 2.2 mA. By utilizing the proposed regulator AC loop shaping, the VCO phase noise sensitivity to supply noise is improved by 30 dB for offset frequency up to 10 MHz with no phase noise peaking.