Research And Design Of Key Technologies For Low-voltage And High-efficiency Analog-to-digital Converters

All kinds of portable devices have become an indispensable part of people's daily life.As the application scenarios of portable devices become more and more extensive,people are increasingly interested in wireless sensor devices for biomedical applications.These sensor devices are usually used for long-term biological signals monitoring,such as electrocardiogram(ECG),electroencephalogram(EEG),electromyogram(EMG).Therefore,the power consumption of circuits used in biological signal monitoring systems has become a focus of attention.Analog-to-Digital Converter(ADC),as a bridge between analog and digital signals,is a key module in a biological signal monitoring system.Therefore,the low power consumption and high energy efficiency of analog-to-digital converters used in biological signal systems have become a valuable exploration direction.Most biological signals change slowly and have low amplitude,so medium precision(8-12bit)and low sampling rate(1-1000 k S/s)are usually required for these ADC.Offset is a problem that cannot be ignored in ADC.Offset will cause the transfer curve of ADC to shift up or down,resulting in loss of high-output code or low-output code of ADC,thus reducing the quantization range of ADC.For low-voltage ADCs whose input signal amplitudes are inherently small,the effects of offsets need to be paid more attention.Aiming at the application of biosignal acquisition system,this thesis designs a lowvoltage ADC for bioelectrical signal quantification.The system is implemented by asynchronous logic.Aiming at the leakage problem of low-voltage ADC,a two-stage bootstrap sampling circuit with negative voltage shutdown function is adopted,which greatly reduces the leakage current in the ADC hold phase.In view of the high common mode of the input signal,the level shift function is added to the capacitor array.Taking into account the driving capability of the front-end amplifier,the requirement for the driving current of the amplifier is reduced by means of level reset.ADCs used in biosignal systems need to consider not only the power consumption but also the pre-and post-stage modules in the system.In a bioelectrical signal system,the ADC is located in the middle of the amplifier and the digital signal processing module.According to such characteristics,this thesis proposes a DAC-based offset voltage measurement scheme,which eliminates the measured offset in the digital signal processing module.The ADC circuit is implemented under the CMOS 180 nm process node,the power supply voltage is 0.6V,the sampling rate is 200 k S/s,the spurious-free dynamic range is 72.91 d B,and the effective number of bits under low-frequency signal input is 9.13 bit.