A 254-nW 20-kHz On-Chip RC Oscillator With 21-ppm/°C Minimum Temperature Stability and 10-ppm Long Term Stability

This paper presents a temperature compensated RC oscillator (TC-RCO) designed in 130 nm CMOS technology using regular $V_{TH}$ transistors. The TC-RCO uses constant transconductance $\left(g_m\right)$ biasing for first order temperature compensation. Device mismatch based offset correction and delay compensation techniques in the comparator are used to improve temperature instability by cancelling out second order effects. The oscillator achieves a minimum temperature stability down to 21 ppm/°C for a temperature range of -20 to 100 °C. In the lowest power mode, the oscillator consumes 254 nW power with a 1 V supply. The TC-RCO is operated in two modes, a low power mode that consumes an average of 254 nW and a high stability mode that consumes an average of 345 nW. A duty-cycling technique is used to correct offset after four cycles of oscillation. The oscillator exhibits long term stability of 10 ppm after 1 s integration time.