A 16-bit sigma-delta modulator for low power medical implantable sensors

We present in this paper the design and implementation of a single-loop second-order CMOS sigma-delta modulator for medical implantable sensors. The modulator circuits features a reduced complexity, power efficient topologies and allow a high resolution of 16 bits. The analog-to-digital converter (ADC) has a sampling rate of 5.12 MHz with an over-sampling ratio of 256, providing a signal bandwidth of 10 kHz. It achieves a 99 dB signal-to-noise-and-distortion ratio at a Nyquist conversion rate of 20 kHz and presents a total power consumption of 1.63 mW. The modulator uses a new fully differential operational amplifier with high performance to realize the integrators. The ADC is being implemented in 0.18 mum CMOS technology, using a supply voltage of 3.3 V.