Ultra-low Power Relaxation Oscillators with Temperature Compensation

A low-power low-TC current source and a piecewise current source are presented by using NMOS transistors with different oxide thicknesses and channel lengths. Two oscillators of 41kHz and 1.15MHz are fabricated in a 0.18-μm CMOS process. Dual-phase cross-coupled structure is used to replace current starving clock buffers which cause considerable power. Furthermore, a high density N-well STI resistor is used to decrease the chip area. For the 41kHz oscillator, its power consumption is 11.3nW with a supply voltage of 0.6V. The average temperature coefficient is 92.8ppm/°C for the temperature of -20~80°C. The calculated power FOM1 and FOM2 are 125.6dB and 95dB. For the 1.15MHz oscillator, its power consumption is 580nW with a supply voltage of 0.8V. The average temperature coefficient is 551.5ppm/°C for the temperature of -20~80°C. The calculated power FOM1 and FOM2 are 123dB and 92dB.