A 1-V CMOS Low-Power Resistor-Based Temperature Sensor for Human Body Temperature Monitoring

Abstract

This paper describes the design and realisation of a CMOS fully-integrated low-power resistor-based temperature sensor for human body temperature monitoring application. The temperature sensing element is realised by an on-chip fully-differential RC filter, driven by a temperature-independent square-wave reference voltage. The fully-differential output voltages of the filter exhibit the temperature-dependent charging and discharging times. A simple voltage comparator is used to compare the filter output voltages and measure the temperature-dependent crossing time. The comparator output voltage is compared with the reference voltage by using an XOR gate, of which the output is a squarewave with a temperature-dependent duty cycle. The temperature variation is measured by calculating the duty cycle or the average DC output value of the XOR output voltage. The proposed temperature sensor was designed and simulated by using process parameters from a standard 0.18-mu m CMOS technology. The overall circuit dissipates 6.96mu W from a single 1-V power supply voltage. Extensive process-corner simulations showed that the proposed circuit could achieve the maximum temperature error of less than ±0. 05 °C over the temperature range of 25°C-45°C.