A programmable dynamic range and digital output rate oscillator-based readout interface for MEMS resistive and capacitive sensors

Abstract

This paper presents a low-cost integrated oscillator-based interface circuit for resistive and capacitive readout. The interface is optimized for MOX gas sensor and can cover a very wide resistive range (100Ω-10MΩ) with an equivalent linearity error of 0.4% (8-bit accuracy), corresponding to 148dB of dynamic range (DR). The architecture cancels the parasitic effects of multiplexing, allowing the conversion of a sensor matrix without decreasing resolution and linearity. Moreover, the same interface can measure capacitive sensors and is optimized to convert sensors in the 1pF-2pF range in 100ms with an accuracy of 3.2e-6 (110dB) at 10Hz of data rate. Programmability of output data rate and DR allows compatibility with different sensors and/or resolution requirements. The interface is implemented in a standard CMOS 130nm technology with an area of 130000μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> including biasing blocks and digital synthesis.