| Brain computer interface is a technology that direct connects brain to external devices.With the help of brain computer interface,brain can convey its intentions to the external world without relying on nerves or muscles.Brain electrical signal acquisition circuit is the part responsible for signal collection in brain computer interface,however,brain electrical signal is usually very weak and easy to be buried in noises,this fact set stringent requirements on the performance of acquisition circuit.Therefore,as a kind of high-performance weak signal acquisition circuit,field effect transistors based signal sensing and amplification circuit has got more and more attention in the field of brain electrical signal acquisition.Based on the mechanism and characteristics of the action potential signal of neurons,a neuron action potential based brain electrical signal acquisition circuit is designed.The main work of this paper is as follows: firstly,according to the analysis of the key points in signal acquisition,an acquisition system is proposed.And then,based on the mechanism of action potential and the noise in the environment,a dielectric layer sensing and input circuit is designed to accomplish high sensitivity signal sensing and coupling.An amplifier circuit for action potential signal is then designed,simulations are carried out for the circuit and each module.Indirect current feedback instrumentation amplifier is designed to achieve low noise and high CMRR.Low frequency suppression circuit is designed to filter the unwanted frequency band to minimize the effects of out-of-band noise.Variable gain amplifier is designed to make the total gain adjustable.The circuit is designed in SMIC 0.18 ?m mixed signal CMOS technology.Simulation results show that the circuit consumes 7.6 ?A current from a 3 V supply.CMRR of the amplifier is higher than 120 dB and the gain band is from 100 Hz to 7kHz,where action potential signal is mainly located in. |
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