ABSTRACT
Advanced semiconductor technologies and sophisticated low-power circuit design techniques are allowing the realization of portable, wearable or implantable biomedical devices in response to increasing interest in healthy living. The physiological signals collected from sensors in biomedical systems are usually very small, on the order of tens of μV to tens of mV, and have considerable noise and offset (Zou et al. 2009). After noise/offset filtering and amplification with the analogue front end (Liew et al. 2009; Yazicioglu et al. 2011), the signal is converted into digital form via an analogue-to-digital converter (ADC) for back-end digital signal processing. Considering the bandwidth of physiological signals (typically less than a few kHz) and the dynamic range (DR) (around 60 dB), ADCs for biomedical applications are usually designed for a resolution of about 8b ∼ 12b and a conversion rate of 1 k ∼ 100 kHz (Yang and Sarpeshkar 2006; Zou et al. 2009). These specifications of resolution and speed can be achieved relatively easily with modern design techniques and processes. However, one of the major concerns in circuit design for portable/implantable biomedical systems is realizing extremely low power consumption. Given that wearable health-care systems sometimes need to monitor signals from the body for more than several days and battery replacement for implanted devices can be very troublesome, the increasing demand for low power consumption is well justified. In addition, considering the possibility of damage to tissues (such as brain cells) by the heat generated from excessive power consumption, the importance of low power consumption has been recognized. Thus, all the 537circuits for biomedical applications, including those for the ADC, should consume as little power as possible.
