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Fully Differential AC-Coupling Networks: A Comparative Study

2008; Institute of Electrical and Electronics Engineers; Volume: 58; Issue: 1 Linguagem: Inglês

10.1109/tim.2008.927200

1557-9662

Óscar Casas, Enrique Mario Spinelli, R. Pallás-Areny,

Advanced Power Amplifier Design

Fully differential ac amplifiers can easily be designed by placing an ac-coupling network in front of a fully differential dc amplifier. Such a network, however, must have a high common-mode rejection ratio (CMRR) to keep the overall CMRR high. In principle, passive ac-coupling networks that include no grounded components have an infinite CMRR, but they must provide a path for input bias currents. This paper analyzes 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.