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

• Published in: IEEE transactions on instrumentation and measurement 2015-12, Vol.64 (12), p.3173-3182
• Main Authors: Koay, Kuan Chuang, Chan, Pak Kwong
• Format: Article
• Language: English
• Subjects: CMOS technology; Converter; Current-mode circuits; current-to-frequency converter; Frequency conversion; low-power current-mode circuit; Low-power electronics; piezoresistive bridge sensor interface; relaxation oscillator; resistive-to-frequency transducer; Sensors; temperature sensor; Temperature sensors; Transistors
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2015.2444256

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/(μΩ/Ω) basing on a center frequency of 1.177 MHz in a half-bridge sensing interface and the quarterbridge temperature sensing interface using a commercial resistance temperature detector. In comparison with the prior-art works, it has demonstrated the best noise-energy figure-ofmerit and comparable linearity in the performance metrics even realized in the environment of nanometer CMOS technology. The sensor interface dissipates only 168 μW at a 1.2 V single supply. Therefore, it is very suitable for portable applications.