Common-mode rejection ratio in current-mode instrumentation amplifiers

Abstract

Abstract. The current-mode instrumentation amplifier (CMIA) based on op-amp power-supply current sensing offers distinct advantages over conventional architecture designs, The CMIA is studied in detail and the CMRR expression is derived in terms of op-amp and transistor parameters. A good CMRR is shown to depend upon several factors, including the power-supply rejection ratio of the op-amps used in the CMIA. The results obtained are shown to compare well with SPICE simulation and provide valuable design insight for development of the next generation of CMIAs.

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

“…As reported in [16], the mismatches between the op amps degrade the CMRR in a higher degree than the mismatches between the current mirrors do. As the parameters a 1 and a 2 depend on the open-loop gain (A d ) and CMRR of the op amps (CMRR OP ), the CMRR of the IA could be improved with a better matching between the op amps and the current mirrors, making their non-idealities as close as possible.…”

“…Reference [9] is a current conveyor-based topology implemented with discrete components, and V i,cm ranging is not reported. Reference [16] is a commercial CMIA supplied through internal chargepumps, providing voltages that exceed the rails.…”

“…In [16] the CMRR of a CMIA is analyzed and modeled. For the topology presented in this paper, where the current mirrors copy only the positive rail current, the CMRR can be approximated at DC as:…”

Current-Mode Rail-to Rail Instrumentation Amplifier for General Purpose Instrumentation Applications

“…4. CMRR calculation in [13,14] also shows that if two of the differential inputs have same gain error, the common-mode effect is minimized.…”

“…An alternative is to use currentmode circuits where CMRR is not directly dependent on resistor matching. In addition, bandwidth is not directly limited by gain in current-mode instrumentation amplifiers [3,[10][11]. The first proposed configuration of Current-Mode Instrumentation Amplifier (CMIA) implementation [4] is depicted in Fig.…”