It is well known that a guard shielded isolation amplifier has a large common mode rejection ratio (CMRR). And it is used in an instrumentation system having many analog inputs. However, the overall CMRR characteristics of an anolog input system that is composed of a signal source, a wiring, a multiplexer and an isolation amplifier was not studied theoretically.
In this paper, we propose the simple equivalent circuit of the circuits composed of the signal source, the wiring, the multiplexer and the input part of the isolation amplifier, its transfer function (IG(s)) and the overall CMRR characteristics as the product of the IG(s) and the AG(s) which is the I/O transfer function of the guard shielded isolation amplifier. And, we introduce the delay time factor (e-S7) in order to express correctly the I/O characteristics of the guard shielded isolation amplifier into the AG (s). To confirm that the theoretical overall CMRR characteristics represent properly the CMRR characteristics of the actual analog input system, we carry out the experiments on the frequency characteristics and the transient response.
J-STAGEがリニューアルされました! https://www.jstage.jst.go.jp/browse/-char/ja/
