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

Postprint (published version

An analog building block for signal conditioning instrumentation circuits

The design of analog signal conditioning circuits for instrumentation applications often requires designing a specific circuit for each case. For board-level design solutions, these circuits are generally implemented by using Operational Amplifiers (OA) and Instrumentation Amplifiers (IA). An analog building block (ABB) is proposed, which can be implemented with three standard OAs. Using different connection schemes and just adding a few resistors, it allows implementing several analog circuits such as common-mode conditioners, single-ended to differential and differential to single-ended converters, voltage and current amplifiers, current-to-voltage and voltage-to-current converters, among others. The proposed ABB is analyzed and applied to several typical analog conditioning problems. The design equations and experimental results for these circuits are presented.Fil: Spinelli, Enrique Mario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; ArgentinaFil: Haberman, Marcelo Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales. Universidad Nacional de La Plata. Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señales; Argentin

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

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.Facultad de IngenieríaInstituto de Investigaciones en Electrónica, Control y Procesamiento de Señale

A fully-differential biopotential amplifier with a reduced number of parts

Objective: Fully differential topologies are wellsuited for biopotential amplifiers, mainly for single-supply battery-powered circuits such as portable wearable devices where a reduced number of parts is desired. A novel fully differential biopotential amplifier is proposed with the goal of providing electrode offset rejection, bandwidth limitation, and a temporal response compliant with biomedical standards with only a single commercial quad operational amplifier (OA) integrated circuit. Methods: A novel compensation strategy was used to provide a transfer function with only one zero at the origin, which makes it easy to comply with the transient response imposed by biomedical standards. A topology with no grounded components was leveraged to obtain a common-mode rejection ratio (CMRR) ideally infinite and independent of components mismatches. Results: Design equations are presented and, as an example, an electrocardiogram (ECG) amplifier was built and tested. It features a CMRR of 102 dB at 50 Hz, 55 dB gain that supports DC input voltages up to ±300 mV when powered from a 0 V to 5 V single-supply voltage, and a cutoff frequency of less than 0.05 Hz with a first order response. Conclusion: A fully-differential biopotential front-end was designed and validated through experimental tests, demonstrating proper operation with only 4 OAs. Significance: The amplifier is intended for board-level design solutions, it can be built with off-the-shelf components that can be selected according to specific needs, such as reduced power consumption, low noise, or proper operation from a low-voltage power source.Instituto de Investigaciones en Electrónica, Control y Procesamiento de Señale