The isolation mode rejection ratio in bioelectric amplifiers

The necessity of a very high isolation mode rejection ratio-the ability of the amplifier to suppress feedthrough from voltages across the isolation barrier to the output-is argued. Two ways of preventing an interference output signal result from isolation mode voltages are described. One approach is to reduce the actual voltage across the isolation capacitance with an additional circuit. Another approach is to design the amplifier in such a way that the feedthrough of high isolation mode voltage remains negligible. It is shown that an eight-channel isolation amplifier with a very good isolation mode rejection ratio can be built with commercially available components, provided that special attention is paid to the shielding of the amplifier inputs. A design of a multichannel amplifier with an isolation mode rejection ratio of 160 dB is described.