A readout circuit with wide dynamic range for differential capacitive sensing applications

Abstract

This paper presents a compact, low power, digitally assisted differential capacitive-sensing readout circuit. It utilizes digital design and switch-based synchronous demodulator to reduce area and power consumption while improving the robustness of the system by diminishing the effects of interfering signals. To broaden the sensing range of the system, the simple implementation of a closed-loop configuration is employed to dynamically adjust the gain. This circuit is designed, analyzed, and laid out in a standard CMOS technology from Austria Microsystems. Post-layout simulation results reveal that the proposed circuit is capable of resolving a minimum of changes in input capacitance under test.Index Terms-Capacitive sensing, feedback loop, interface circuit.

Design of CMOS readout frontend circuit for MEMS capacitive microphones

“…Moreover, sensitivity and input noise as well as the noise floor obtained by this approach are better than those presented in [31]. The proposed readout circuit requires smaller chip area than in approaches presented in [29] and [30]by 18% and 23% higher than [27] and [31], respectively. Finally, in comparison to other works, the most important improvements and features of the presented readout frontend circuitry can be summarized as follows:…”

“… broader dynamic range  better noise performance  low power consumption However, these features are achieved at costs of area overhead (about 20% with respect to works presented in [27] and [31]).…”

“…The achieved results show that the proposed approach brings the high dynamic range and very good noise performance, which are the most important parameters required by a MCM-based noise dosimeter meant to be used in very harsh environment. [27] [ Currently, the developed readout interface is being fabricated. In the future research, evaluation of prototype chips will be performed and possible modification of the RI design towards further improvements is expected.…”

“…The reset noise reduction schemes [26] also include a feedback loop that either cancels the reset noise or reduces the bandwidth of noise or controls the reset process itself. Interesting concept was presented in [27], where electro-mechanic feedback incorporates a triangle voltage wave generator. In combination with the constant-voltage approach and transimpedance amplifier, high dynamic range was achieved.…”

“…Therefore, main advantages include broad dynamic range, low power consumption and robustness against the environmental noise. However, the vast majority of realizations do not meet the readout circuit requirements for MEMS microphones [22][23][24][25][26][27].…”