Impedance-to-digital converter for sensor array microsystems

Many emerging micro/nano sensor interfaces suitable for microsystem integration produce a change of impedance that must be monitored over a broad frequency range. This paper introduces a mixed-signal integrated circuit that can extract and digitize the real and imaginary components of a sensor´s impedance response. The ultra compact size of this circuit enables each element in a multi-channel sensor array microsystem to have its own individual readout channel, permitting simultaneous readout and digitization of a high density sensor array. The circuit was fabricated in 0.5 mum CMOS and occupies only 0.045 mm² per cell. With a 3.3 V supply, each cell consumes only 5.2 muW at a typical 200 kHZ sampling frequency. For a 3 mm by 3 mm die, this circuit can be instantiated well over 100 times, which is sufficient for the needs of many anticipated sensor array microsystems.