Ultra low power Analog-to-Digital Converter for Biomedical Devices

Abstract: The biomedical devices often operate only with a battery, e.g., blood glucose monitor, pacemaker. Therefore, it is desirable to fully utilize the energy without sacrificing the performance of the system. The Analog-to-Digital Converter (ADC), as a key component of most of the biomedical devices, needs to be designed for minimum power consumption by exploring various techniques from system level to circuit level. In addition, the nature of bio-signal provides more alternatives to reduce the power. In this thesis work, an 8 bit 11 kS/s modified algorithmic analog-to-digital converter for biomedical applications is proposed. All analog components are designed at circuit level using a 90 nm CMOS technology and digital components are implemented using Verilog-A language in Cadence. The ADC is operating in current mode at sub-threshold region with only 0.5 V supply voltage with an input current from 0 nA to 512 nA. The ADC is designed based on a top-down design with bottom-up verification approach. The system level model is described using top level language and then the circuit level is created and verified using Cadence tools according to the system level model. The INL and DNL obtained from simulation is -1/+0.8 LSB and -0.9/+1 LSB respectively. The SNDR is 47 dB (7.5 ENOB) for a -0.2 dBFS at 1 kHz sinusoidal signal. The power consumption is 2.83 μW without biasing and 4μW with biasing.