An area-efficient on-chip temperature sensor with nonlinearity compensation using injection-locked oscillator (ILO)

This paper describes CMOS time-domain temperature sensors. A principle of this type of sensors is CMOS inverter's time-delay variation with temperature. The variation, however, has nonlinearity which is a fundamental error source. Therefore, we propose a new temperature sensor that improves linearity using an injection-locked oscillator (ILO). Since the ILO has the opposite curvature of an inverter delay line in temperature domain, nonlinear error induced by the CMOS inverters can be eliminated. Integral nonlinearity (INL) error is reduced from 3.6 LSB to 0.56 LSB (84% reduction), resulting in under 1-bit error by nonlinearity. The proposed design has -0.19°C~0.2°C inaccuracy which is only quantization error over 0°C~100°C. The power consumption is 2.88mW including an 8-bit temperature-to-digital code conversion block at the sampling rate of 15.6M samples/s.