Fully-Differential AC-Coupling Networks: A Comparative Study

OSCAR CASAS; ENRIQUE SPINELLI; PALLAS ARENY

IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT

IEEE

Año: 2009 vol. 58 p. 94 - 98

0018-9456

Fully-differential ac amplifiers can easily be designed by placing an ac coupling network in front of a fully-differential dc amplifier. That network, however, must have a high common-mode rejection ratio (CMRR) to keep the overall CMRR high. Passive ac coupling networks that do not include any grounded component have in principle infinite CMRR but they must provide a path for input bias currents. This paper analyses how component tolerances limit the CMRR and affect the transient response of three different ac coupling networks. To evaluate these networks in real conditions, the common mode input impedance and bias currents of the ensuing differential amplifier are considered. Experimental results confirm the theoretical predictions.