An energy-efficient reconfigurable readout circuit for resonant sensors based on ring-down measurement

This paper presents a novel readout circuit for micro-mechanical resonant sensors. To determine the sensor´s resonance frequency and quality factor, the sensor is briefly excited, after which the exponentially-decaying ring-down current produced by a piezoelectric transducer is read out by an auto-zeroed trans-impedance amplifier (TIA). An auto-zeroed comparator then detects zero- and level-crossings for frequency counting and quality factor measurement. A new circuit topology is proposed to reduce errors due to leakage currents. Moreover, a reconfigurable TIA enhances the circuit´s flexibility. A prototype chip has been implemented in a 0.35 μm CMOS process. Experimental results obtained using a silicon-nitride clamped-clamped beam resonator are in good agreement with results obtained using conventional impedance analysis. In a measurement time of 2 ms, the circuit achieves a 50 ppm detection limit in resonance frequency, 5 times better than prior work, while consuming only 31.5 μA from a 3.3 V supply.