The configuration of the amplifier for recording the ionic channel current of the cell is described here.The measured currents vary from 1 pA to nanoampers

and the output voltage is required to be processed by the computer.Therefore

the amplifier must be constructed in multistages.The key point for designing this amplifier is the low noise technique

especially for the headstage.The background noise of the main components and devices are particularly analyized with power density spectrum

S

I

(f)

and

S

v

(f

) to characterize their characteristics.The test results of the designed patch clamp amplifier model PC-Ⅱ satisfy the practical requirement and the experimental data are given.