A Low-Power Resistance-to-Frequency Converter Circuit With Wide Frequency Range

Abstract

A 65-nm CMOS front-end relaxation oscillator- based interface circuit for resistive bridge sensors is presented. It converts the sensor ac input currents into the sawtooth frequencies through the use of the proposed direct current-sensing grounded integrator topology without resorting to any current mirror(s) for coupling or signal processing in current-mode circuit design. Validated by three test setups in experiments, the proposed work shows a sensitivity of 41.5 Hz/nA dedicated to the wide output frequency ranging from 1.3 kHz to 2.489 MHz in a current-to-frequency converter, a sensitivity of 44.43 Hz/( $\mu \Omega/\Omega $ ) basing on a center frequency of 1.177 MHz in a half-bridge sensing interface and the quarter-bridge temperature sensing interface using a commercial resistance temperature detector. In comparison with the prior-art works, it has demonstrated the best noise-energy figure-of-merit and comparable linearity in the performance metrics even realized in the environment of nanometer CMOS technology. The sensor interface dissipates only 168 $\mu \text{W}$ at a 1.2 V single supply. Therefore, it is very suitable for portable applications.