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A Capacitance-Ratio-Modulated Current Front-End Circuit With Pulsewidth Modulation Output for a Capacitive Sensor Interface

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3 Author(s)
Meng-Lieh Sheu ; Dept. of Electr. Eng., Nat. Chi Nan Univ., Puli, Taiwan ; Wei-Hung Hsu ; Lin-Jie Tsao

This paper presents a front-end circuit with pulsewidth modulation (PWM) output for a capacitive sensor interface. A single-MOSFET-based capacitance-ratio-modulated current (CRMC) circuit is proposed to transform the sensed capacitance into a current proportional to a capacitance ratio. The proposed single-MOSFET-based CRMC circuit not only saves a lot of chip area but also lowers power consumption. Then, a dual-slope integration circuit transforms further the modulated current into PWM output. A prototype chip is designed and fabricated with a 0.35-μm complementary metal-oxide-semiconductor process and has a core area of 0.09 mm2. The measurement results of the prototype chip demonstrate an accuracy value of up to 9.3 bit with 54-μW power consumption. The microwatt power consumption and the small chip area of the proposed front-end circuit make it very suitable for a capacitive sensor interface in smart sensor chips.

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Instrumentation and Measurement, IEEE Transactions on  (Volume:61 ,  Issue: 2 )