A TDC-Based Temperature Sensor for Biomedical Applications

A TDC-based temperature sensor is implemented using 0.18-
$\mu {\mathrm{ m}}$
CMOS technology for thermotherapy. The temperature sensor is composed of a temperature-to-pulse generator (TPG) and a time-to-digital converter (TDC). The TPG consists of two delay lines with different temperature coefficients, where one of the delay lines is realized by using the temperature compensation, so it is almost temperature independent. The TDC is based on a pulse shrinking architecture, where the number of the shrinking element and unit delay determine how the pulse is reduced in each cycle. The design flow is first proposed to facilitate the design process. Moreover, the impact of process variation is considered for the shrinking element. The resolution of 0.054°C is achieved by the temperature sensor. After the two-point calibration, the inaccuracy is ± 0.2°C for the temperature range from 25°C to 45°C. The temperature sensor consumes 0.65 uJ for each sample while achieving the conversion time of 100 ms. The chip size is 0.47 mm
²
.