Low Power Data Acquisition System for Bioimplantable Devices

Signal acquisition represents the most important block in biomedical devices, because of its responsibilities to retrieve precise data from the biological tissues. In this paper an energy efficient data acquisition unit is presented which includes low power high bandwidth front-end amplifier and a 10-bit fully differential successive approximation ADC. The proposed system is designed with 0.18？μm CMOS technology and the simulation results show that the bioamplifier maintains a wide bandwidth versus low noise trade-off and the proposed SAR-ADC consumes 450？nW power under 1.8？V supply and retain the effective number of bit 9.55 in 100？KS/s sampling rate. 1. Introduction In the past few years, the rapid developments in the field of microelectronics and VLSI have driven forward the advent of implantable medical sensors and devices. Multichannel devices are emerging due to the fact of recording numerous number of biological tissue activities collectively [1]. Such multichannel sensors first collect the extracellular signals from a micromachined array including several electrodes and process them through embedded microelectronic circuits for conditioning, multiplexing, and digitization. A fully implantable recording device would then wirelessly transfer the digital data through an inductive link to an external controller. As the capability to integrate more recording channels is growing, suitable data acquisition systems are needed to meet smaller silicon area and lower power dissipation requirements [2]. Biopotential signals, such as electrooculogram (EOG), electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (ECG), cover a wide range of spectrum and signal bandwidth ranging from few hertz to 10？kHz [3] and the acquired signals through dense microelectrode arrays are very low in amplitude and susceptible to environment noises [4]. Proper processing of these signals requires amplification and noise cancellation, digitization, and digital signal processing before being considered for analysis. Figure 1 shows the block diagram of the proposed system architecture. Figure 1: System overview. Bioamplifiers are the primary building blocks in biomedical sensing devices [5]. The most common characteristics of bioamplifiers are band pass characteristics, DC offset, low noise or noise reduction, and reduced power consumption. For designing bioamplifiers the power dissipation should be restricted to several orders of below 80？mWcm？2 [6] in order not to harm the tissues. Implantable bioamplifiers must dissipate little power so that surrounding tissues