Design Approaches of Ultra-Low Power SAR ADC for Biomedical Systems — A Review

Abstract

In recent years, implantable biomedical devices like cardiac pacemaker, defibrillators, cochlear implants, visual prosthesis etc. have gained immense importance in the personal health monitoring system. Most of these devices are battery powered. The life span of a pacemaker is expected to be between 10 and 12 years. This shows the importance of having an ultra-low power design technique to improve the reliability and battery life of the system. To achieve this, power draws from the battery must be kept low. Analog-to-Digital Convertor (ADC) is a main block in the front-end sensing unit of an implant for measurements of various biophysiological signals. This is the most power consuming unit in the system. ADC alone consumes about 30%–35% of the total power. This work surveys various successive approximation ADC designs for biomedical signal acquisition, in terms of power consumption, signal to noise distortion ratio, sampling rate, resolution and Figure of Merit. The different switching schemes for capacitive DAC are also surveyed.