A 40nm-CMOS, 18 μW, temperature and supply voltage independent sensor interface for RFID tags

Abstract

A fully-integrated, oscillator-based sensor interface for RFIDs and low-power applications is presented in this article. The circuit is processed and tested in a 40 nm CMOS technology. The interface translates the analog sensor signal, coming from a differential sensor, into a Pulse width Modulated (PWM) signal of which the duty cycle is proportional to the sensor value. Due to the high control linearity of the used oscillator, the interface has a low nonlinearity and can be made highly temperature and supply voltage independent. The total power consumption is 18 μW at 1.0 V and the interface works over a 0.8 to 1.5 V supply voltage range and a -20 to 100°C temperature range. The voltage dependency is below 1.42 %/V and the maximum temperature dependency is 79 ppm/°C. The oscillator frequency is slightly above 2 MHz in all circumstances. The measured SNDR of 47.4 dB results in a FOM of 66 fJ/b-conv.