A low-voltage adaptive Switched-Current SDM for bio-acquisition microsystems

An ultra-low voltage and low-power adaptive Switched-Current Sigma-Delta Modulator (SISDM) with a 10-bit dynamic range for bio-microsystem applications is presented. In order to achieve the low-voltage requirement, a novel class-AB switched-current memory cell is adopted to implement the SISDM with the over-sampling ratio (OSR) of 64. In addition, a proposed differential current comparator and a low-voltage 1-bit Switched-current Digit-to-Analog Converter (SIDAC) are used for the design of the SDM. Benefits from the SISDM using the class AB memory cell are low-power consumption, high linearity, and high dynamic range. For the various applications with different biosignal frequencies, the SISDM could be operated in different operation mode. The overall SDM with core area of 0.05mm(2) has been implemented in a TSMC 0.18 mu m 1P6M standard CMOS process technology. Without voltage booster to raise the gate voltage of switches, post-layout simulation results show that the SISDM has a dynamic range over 60dB and a power consumption of 180 mu W with an input signal of 1.25kHz sinusoid wave and 5kHz bandwidth under a single 0.8V power supply for ENG signals.