An Amplifier for Fetal Electrocardiography

Abstract

An amplifier is described which uses several novel techniques to reduce noise and interference during recordings of fetal ECG from the mother's abdomen. Emphasis in the design has been placed on patient safety.

The preamplifier section is powered by rechargeable batteries and isolated from the main unit by GaAs photo-diode pairs. FET-input amplifiers reduce electrode artifacts by increasing input impedance and reducing bias current. A voltage clamp is used to simulate a differential input, resulting in a high common-mode rejection ratio and a simplification of circuitry.