An optocoupler isolation amplifier with MHz bandwidth is designed based on HCNR201.It is mainly used in computer data acquisition system

and isolates the signal to realize over-voltage protection and improve the common mode rejection ratio.The HCNR201 consists of double photodiodes which can form a feedback loop in the input port to eliminate the impact of current transfer ratio of the optocoupler on the DC gain.This paper presented the equivalent circuit of HCNR201 for facilitate analysis.This paper built mathematical model of the circuit

derived the transfer function

and gave theoretically analysis and optimized the parameters.We presented the analysis and design results

and the experiment test of the circuit consistent with theoretical analysis is given.The optocoupler isolation amplifier meets the requirements and the theoretical analysis method can provide reference for similar circuit design.