Design Of Driving Circuit Applied For Neural Signal Regeneration

In terms of neural dysfunction caused by spinal cord injury problems,professor Zhigong Wang' team in southeast university put forward a auxiliary treatment method of "Microelectronics Nerve Bridge".It uses microelectrodes to connect electronic devices on both ends of the damaged nerve,replacing the original biological electrical signal pathway with a man-made signal path,to reconnect the interrupted nerve channel,and to recover the damaged spinal cord function."Microelectronics Nerve Bridge" consists of a detection circuit,a signal processing circuit and a regeneration circuit.The research content of this paper is about the terminal module of "microelectronic neural bridge" ——regeneration of nerve signals.The function of the circuit is to amplify the output signal of the front-stage circuit to a sufficient voltage swing.Then the voltage is applied to the injured nerve terminal through the electrode,driving the nerve cells to generate action potential,and realizing the regeneration of nerve signal at the terminal nerve.In the realized in vitro regeneration module of animal nerve signals,the output of the circuit is-2.5V~+2.5V.In view of the asymmetric characteristics of positive and negative voltage of nerve cell membrane potential,-1V ~4V circuit output index is adopted in this paper to improve the stimulation effect.Aiming at the improved output index,a new circuit structure is designed,combining an on-chip integrated amplifier and an off-chip output circuit,which is different from the previous one.The amplifier adopts full swing input structure,which can process common mode signals in a wide dynamic range.Use the maximum current selection circuit and the transconductance equivalent circuit to keep the transconductance of the amplifier constant throughout the common mode input range.In this paper,a band gap reference source is designed to provide a stable bias for the amplifier to reduce the influence of temperature change and power supply voltage fluctuation on the circuit.Referring to the first order compensation characteristic of common bandgap reference,the CTAT current injected by the emitter of triode is used to obtain the negative high order temperature term corresponding to the positive high order temperature term,which further reduces the temperature coefficient.The off-chip output circuit is designed with a high-voltage MOSFET,and the output impedance of the circuit is equivalent to the load resistance connected to the drain pole of the MOSFET,avoiding other additional devices and reducing the complexity of the off-chip circuit.The on-chip circuit adopts TSMC0.18 ?m CMOS process to design.The chip area is 300?m×300?m,and the power consumption is about 1.45 mW at the supply voltage of 1.8V.The temperature coefficient of bandgap reference voltage is 7.03 ppm/°C,The common mode input range of the amplifier is 0.12 V ~ 1.75 V,basically reaching full swing input;In the whole common mode input range,the transconductance change rate of the amplifier is 6%;the open loop gain of the amplifier is 82 dB,and bandwidth is about 2MHz.Through ac simulation of the amplifier at different temperatures,it is found that the voltage gain is within the range of 79 dB to 89 dB in the whole temperature range,and the gain does not change much.The off-chip output circuit operates under the external power supply of +5V and-1.5V.The whole circuit adopts feedback resistors to form a closed-loop amplifier with a gain of 40 dB.At the input signal of 50 mV,the circuit output reaches the voltage swing of-1~4V.