Interface electronics for MEMS-based wireless sensing applications

High-performance interface electronics design for two MEMS-based wireless sensing applications, (1) strain sensing and (2) implantable blood pressure sensing, is presented. In a wireless MEMS strain sensing microsystem, a MEMS capacitive strain sensor is interfaced with a custom-designed ASIC consisting of a low-noise continuous-time synchronous-detection capacitance-to-voltage converter and a 2^nd-order ΣΔ ADC to digitize the strain information for a reliable wireless data transmission. An on-chip temperature sensor and a 1st-order ΣΔ ADC are included for system calibration. The microsystem is powered by a 51.2MHz signal and can simultaneously telemetry two channels of digitized strain and temperature data over the RF powering link by passive PSK and ASK modulations, respectively. The prototype system achieves a minimum detectable strain of 50ne over a 10kHz bandwidth with a maximum DC input signal of +/-1000με, and dissipates 2 mA from an on-chip 3V supply. In a wireless implantable blood pressure sensor design, a low-power integrated electronic system is employed, consisting of a capacitance-to-voltage converter, an 11-bit ADC, an adaptive RF powering system, an oscillator-based 433MHz FSK transmitter and digital control circuitry. The packaged microsystem achieves a capacitive sensing resolution of 75aF over 1 kHz bandwidth, equivalent to a pressure sensing resolution of 1mmHg inside a blood vessel, with a dynamic range of 60dB while dissipating 300μW power.