Nanopower CMOS Relaxation Oscillators With Sub-100 $\hbox{ppm}/^{\circ}\hbox{C}$ Temperature Coefficient

A low temperature coefficient (TC) current reference and a curvature current source are realized by transistors with different gate-oxide thicknesses. These two current sources are used to realize oscillators with low TCs. These two oscillators of 1.4 MHz and 28 kHz, respectively, are fabricated in the 0.18-μm CMOS process, and their areas are 0.072 and 0.16 mm2, respectively. For the 1.4-MHz oscillator, its power is 615 nW with a supply voltage of 1.2 V. The measured average TC is 56.4 ppm/°C for a temperature of -20 °C to 80 °C. The calculated figures of merit (FOM1 and FOM2) are -131 and 103 dB, respectively. For the 28-kHz oscillator, its power is 40.2 nW with a supply voltage of 1.2 V. The measured average TC is 95.5 ppm/°C for a temperature of -20 °C to 80 °C. The calculated FOM2 is 92 dB.