Design of a temperature-insensitive digitally-controlled oscillator for on-chip reference clock

This paper presents a 0.4V temperature-insensitive digitally-controlled ring oscillator (DCO) for on-chip reference clock circuit. Based on a modified bootstrapped ring oscillator (BTRO), temperature variation can be further decreased without calibration, where BTRO is operated at near-threshold voltage. A binary-weighted tree-controlled resistor network (BWTRN) is performed to achieve an 8bit high-linearity DCO with BTRO. The proposed DCO is fabricated in TSMC 90 nm CMOS process with a core area of 0.013 mm2. The simulation results in typical corner demonstrate that the DCO oscillates max/min frequency of 105.6MHz/60.7MHz at 0.4 V Vdd and consumes 8.77μW/4.44μW. The maximum temperature variation of the single code is 329 ppm, and its maximum DNL variation is 0.67 LSB. Even for all process corners, the maximum temperature variation among all control codes is 8%.