Research And Design Of SAR ADC For Biopotential Acquisition System

Biopotential signals can reflect the basic physiology of human body, it can be used to provide diagnostic evidence for clinical care and disease prevention by signals acquisition and processing. Analog-to-digital converter(ADC) plays an important role to connect analog front-end potential acquisition circuit and digital back-end processing circuit, which is the core module in biopotential acquisition system. SAR ADC has been widely used for its advantages of simple structure, low power and small area.In this paper, aiming at the application in biopotential acquisition system, studying and designing a low power 10-bit 100kS/s fully differential switched capacitor SAR ADC.First of all, This work design a split capacitive DAC with top plate sampling methods and VCM-based switching schemes, reducing the chip area and power consumption. And12-bit split capacitive DAC structure is adopted to achieve 10-bit resolution to reduce the nonlinear error introduced by bridge capacitance, increasing the effective number of bits.Secondly, in the comparator, the preamplifier cascoded by three amplifiers with dynamic latch is used to increase comparing speed. With the calibration method of output offset storage, reducing the influence of the offset voltage of the comparator. At last, SAR control logic and switch networks are designed to control DAC and comparator to complete the process of offset autozeroing, sampling, comparing and sleeping, finishing the whole process of analog to digital converting, and make the system-level simulation.SAR ADC has been implemented with SMIC 0.18?m CMOS process, the power supply voltage is 1.8V. The circuit is simulated by Spectre tool. The results show that, the SNDR is 59.97 dB, ENOB is 9.67, DNL is +0.3LSB/-0.1LSB, INL is +0.4LSB/-0.5LSB,an average power consumption is 24.12?W. The parameters are excellent and meet the performance requirements of ADC for biopotential acquisition system.