Title: A design method for active high-CMRR fully-differential circuits

Authors: Enrique Mario Spinelli; Gemma Hornero; Oscar Casas; Marcelo Haberman

Addresses: Industrial Electronics, Control and Instrumentation Laboratory (LEICI), Faculty of Engineering, National University of La Plata, CC 91 – (1900) La Plata, Argentina ' Instrumentation, Sensors and Interfaces Group, Escola d'Enginyeria de Telecomunicació i Aeroespacial de Castelldefels (EETAC), Technical University of Catalonia (UPC), 08860 Castelldefels, Spain ' Instrumentation, Sensors and Interfaces Group, Escola d'Enginyeria de Telecomunicació i Aeroespacial de Castelldefels (EETAC), Technical University of Catalonia (UPC), 08860 Castelldefels, Spain ' Industrial Electronics, Control and Instrumentation Laboratory (LEICI), Faculty of Engineering, National University of La Plata, CC 91 – (1900) La Plata, Argentina

Abstract: A simple method for designing instrumentation fully-differential (FD) circuits based on standard single-ended (SE) operational amplifiers (OAs) is presented. It departs from a SE prototype that verifies the desired differential-mode transfer function, thereby leading to FD versions of the circuit. These circuits have a high common mode rejection ratio (CMRR), independent of component imbalances, and a unity common-mode gain. The proposed method does not allow the design of common-mode response, but it does verify common-mode stability, thus ensuring stable FD circuits. It is intended for instrumentation applications in which high CMRRs are required. The proposed approach makes it possible to design and implement inverter and non-inverter topologies as well. Design examples and experimental data are presented. Using general-purpose OAs and 5%-tolerance components, the CMRR of these circuits easily exceeds 90 to 100 dB.

Keywords: instrumentation circuits; operational amplifiers; OAs; differential circuits; fully-differential processing; analogue signal processing; circuit design; common mode rejection ratio; CMRR.

DOI: 10.1504/IJIT.2012.053281

International Journal of Instrumentation Technology, 2012 Vol.1 No.2, pp.103 - 113

Received: 21 Dec 2011
Accepted: 22 Jun 2012
Published online: 17 Sep 2014 *

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