the invention comprises an isolation amplifier including an input circuit and an output circuit coupled through an isolation transformer . a switching type balanced modulator modulates a square wave carrier with an analog signal input and delivers the resulting signal to the input of the isolation transformer . a demodulator in the output circuit inverts alternate points of the modulated square wave carrier to essentially reproduce the analog input . a sample and hold capacitor circuit connected to the output of the demodulator fills the gap between the trailing and leading edges of successive pulses .