This paper describes an analog circuit for airborne radioactive iodine detector .In the design of the detector , the traditional design idea of separating preamplifier and main amplifier has been abandoned ,replaced by setting the pre-amplifier and the main amplifier as a whole in the probe .In order to achieve long distance transmission of analog signal ,a drive circuit is provided at the front end of the cable ,which has the function of impedance matching and current amplification .The drive circuit achieves the goal of no need to match the im-pedance in the rear end of the signal cable ,it ...