Research And Design Of High Performance Instrumentation Amplifer For Biopotential Signals

The instrumentation amplifier for biopotential signals plays an insignificant role in detecting and sensing biopotential signals in various medical electronic devices.It can be employed in the diagnosis of various diseases such as epilepsy,cerebrovascular disease and heart disease.In the meantime,it can be used in the intelligent biomedical electronic devices,such as the cochlear implant,artificial retina and intelligent prostheses.In consideration of the low amplitude of biopotential signals,the instrumentation amplifier for biopotential signals must have low noise and low offset,therefore,this thesis focuses on the research about achieving the performance of low noise and low offset.Firstly,this thesis illustrate the sources of noise and offset of the instrumentation amplifier and then analyses auto-zeroing technique and chopping modulation technique for the cancellation of the instrumentation amplifier's noise and offset.After that,several typical topologies of instrumentation amplifier for biopotential signals are compared.The capacitively-coupled chopper instrumentation amplifier is discussed in detail and the design of the ripple reduction loop for the suppression of output ripple is described.This thesis mainly designs two capacitively-coupled chopper instrumentation amplifiers.One of them is a current-reuse capacitively-coupled chopper instrumentation amplifiers that uses current-reuse techniques in the main amplifier and ripple reduction loop and reduce the overall power consumption.Also,Ping-Pong auto-zeroing technique is employed in the ripple reduction loop to shorten the time of the instrumention reaching the stable state.The other one is instrumentation amplifier with adjustable gain and bandwidth.Its main features are as follows:(1)Using chopping modulation technique,current-reuse technique and sub-threshold MOS transistors to achieve low-noise and low-power performance;(2)Combining Ping-Pong auto-zeroing technique and DC blocking capacitors to eliminate the output ripple of the chopper instrumentation amplifier;(3)Using an adaptive electrode offset suppression loop to suppress the about 50mV electrode offset voltage while reducing the input referred noise which electrode offset suppression loop contribute to;(4)Adding a positive feedback loop to enhance the input impedance of the instrumentation amplifier;(5)Setting a variable gain amplifier and variable capacitors to make the gain and the bandwidth of the instrumentation amplifier adjustable and accommodate the actual needs of various biopotential signals.Finally,the chip for verification is fabricated in Global Foundry 0.18p.m BCD 1P6M process.The simulated result shows the supply voltage of the instrumentation amplifier is 1.8V,the quiescent current is 4.2?A.The gain can be set as 40dB,46dB,52dB,58dB respectively,the high-pass cutoff frequency is about 0.1Hz,the low-pass cut-off frequency can be set to 1kHz and 10kHz.And the equivalent input noises are 54nV/? Hz and 55.4nV/? Hz and the noise power factors are 4.25 and 4.36 in 1kHz and 10kHz bandwidth respectively respectively.The common mode rejection ratio is 95dB and the input impedance is about 50M?.