A low power temperature sensor based on a voltage to time converter cell

In this paper we propose a temperature sensor, based on a voltage to time converter cell (VTC). A VTC is frequently employed in time to digital converters for generating a delay that is proportional to the input voltage. The delay can then be digitized using a simple ripple counter at the output driven by a temperature independent clock. The power consumption of the proposed sensor is extremely low at 250nW, with an inaccuracy of +0.8°C to -1.5°C after two point calibration. A comparator with switchable bias currents is used to reduce the power consumption, while the temperature compensated current source is implemented using a low power current source. The sensor also exhibits high linearity over the 0 to 100 °C temperature range, while being powered by a 1.8V supply.