Abstract: A time division multiplexing amplifier having a differential amplifier, such as a dynamic bridge amplifier, which has a predetermined gain accurately provided by means of operational network resistors. The differential amplifier is used to amplify differential signals containing a common-mode voltage. Prior to amplification of the differential signals, a common-mode voltage is applied in common to two input terminals of the differential amplifier, and then the differential amplifier is adjusted to provide a zero offset voltage. After that, the differential signals are applied to the differential amplifier, so that the differential signals can be amplified without having any adverse effect of a common-mode voltage.

Abstract: In measuring analog input voltages through isolation transformers, an analog input voltage V.sub.in is applied across a primary winding of the isolation transformer, voltages V.sub.A and V.sub.B developing across the secondary winding of lapses of time T.sub.A and T.sub.B (T.sub.A < T.sub.B) from application of the analog input voltage are detected, and by using measured times T.sub.A and T.sub.B and secondary winding voltages V.sub.A and V.sub.B, the analog input voltage V.sub.in is calculated in accordance with an expression ##EQU1## whereby influence of sag due to the isolation transformer is compensated for.