An Integrated Circuit Design Of Dualmode Neural Stimulator

The development of medical electronic for people of psychiatric disease provides a solution to many of the human body organs nerve damage caused by a functional disorder can through the use of nerve stimulator to the body tissue nerve stimulation applied charge way to restore normal movement function,such as spinal cord stimulator,deep brain stimulator,pacemakers and other applications.The implantable nerve stimulator is an effective treatment for some nerve damage diseases which are easy to repeat for a long time.Such electronic instruments require miniaturized,low-power neural stimulation chip circuit as the source of stimulation,in order to make the instrument has a longer working life.This paper focuses on the design of an efficient neural stimulation chip circuit,which USES a double-mode output stimulation mode,including rectangular voltage output mode and exponential current output mode.The circuit structure mainly consists of shift register,current mode R-2R DAC,exponential current generation circuit,current detection circuit and other parts.The shift register is built by D flip-flop as the basic unit,which can convert the SPI signal into the 6bit data encoding required by DAC,and the two-bit mode selection signal required by the current detection circuit.The 6bit R-2R DAC external operational amplifier in two current modes acts as an I/V converter to obtain a voltage pulse output for stimulating the human body,while the voltage output of the DAC provides control over the amplitude of the exponential current pulse circuit.Another output mode is the exponential current output obtained by using the exponential function Taylor series approximation combined with the characteristics of CMOS transistor.The choice of the two output modes is controlled by the single-pole double-throw switch formed by the transmission gate structure,and small resistors are used in series at the output end for current sampling and access to the current detection circuit structure,so as to achieve the effect of real-time control of the stimulus intensity and realize the current detection range of three blocks.The current detection circuit mainly uses the buffer circuit and subtracter circuit to amplify and output the voltage difference on the small resistance to obtain the measurable voltage output.This paper is based on the 180 nm process library provided by Silterra company of Malaysia for circuit structure design,layout drawing and post copy,and the flow sheet work has been completed.The circuit uses double power supply ±2V for power supply,the reference voltage value of R-2R DAC is set as ±1.8V,and the lowest significant bit is 28.125 m V.The overall circuit can output voltage stimulus pulse with amplitude ranging from-1.8V to 1.8V and exponential descending current stimulus pulse with intensity not exceeding 400?A.The maximum detection range of current detection circuit is 1m A,and the detection accuracy can reach 12.5n A.The working current of the whole circuit does not exceed 3.2m A.