A novel current mode instrumentation amplifier (CMIA) topology

Abstract

A novel CMIA configuration based on CCII+ is presented. Some of the advantages of this configuration over the traditional Voltage Mode Instrumentation Amplifier (VMIA) are: a wideband differential voltage gain independent of gain magnitude and a high common mode rejection ratio (CMRR) without requiring well-matched resistors. Compared to other previously presented current mode instrumentation amplifiers (CMIAs), each of which showed a limited number of special advantages, this topology benefits from most of those individual advantages, those being: small size, circuit simplicity very inexpensive price, complete circuit symmetry, high voltage gain, and CMRR. In addition, due to the application of the current feedback technique, the topology has acquired further superior qualities such as weaker voltage and current error signals, making it ideal for working with general purpose ICs, higher voltage gains, and much higher CMRR than other topologies. A suggestion is also given to widen the CMRR bandwidth. To prove these advantages and superiorities, a detailed theoretical analysis is given as well as some experiments being performed with AD844AN (the general purpose type) inside a Faraday's cage, with an attenuation better than 60 dB. Both theoretical and experimental investigations are repeated for Wilson and Kaulberg topologies which are claimed to be the best configurations. Results are compared to prove the advantages of the new topology.