The microelectrode technique for recording the electrical activity of a single biological cell is developing rapidly

which requires the development of biological amplifers to follow up.This article describes a new type of amplifier designed to meet the requirements. Owing to the adoption of a differential cascade circuit and the application of strong negative -feedback around the amplifier

the following performance of the amplifier is obtained: input impedance—10

11

Ω is parallel with 1 pf（with optimum compensation）

common mode rejection ratio—greater than 10

4

drift—200 μf/30 min

frequency response—0-200 kc/s（—2db）

grid current—less than 2×10

-12

A.This performance is superior to that of current types of the so-called "cathode followers". This amplifier has been used for 3 years in the biological laboratories of our institute and proved reliable and of good quality.