Current mode instrumentation amplifier with rail-to-rail input and output

This paper presents the results from an investigation on the implementation of Current Mode Instrumentation Amplifiers (CMIAs) with rail-to-rail operational amplifiers (op amp) with a gm control circuit. The objective of employing rail-to-rail op amps in the implementation of a CMIA is the improvement of the common-mode operation range. The enhancement of the input common mode range (ICMR) is obtained using op amps with a rail-to-rail input stage followed by a cascode-based output stage. A prototype of the CMIA was implemented in standard 0.6 μm XFAB CMOS technology. Test results showed that the CMIA common mode range was extended but with moderated CMRR. To minimize this issue the amplifier was re-designed and sent to fabrication. Simulations with the components variations included were performed and showed the enhancement of the CMRR can be expected.