CMRR Enhancement Technique for IA using Three IAs for Bio-medical Sensor Applications

This paper presents a high CMRR Instrument Amplifier (IA) for bio-medical circuits, which employs three identical low-CMRR IAs to enhance the CMRR. In order to achieve high CMRR, proposed IA consists of two stage cascaded differential amplifiers, where differential gain is enhanced, but the common-mode gain is reduced due to cascading. The analysis on the non-ideal effects such as mismatch of the common mode gain and differential gain between IAs is described. Simulation results show that the proposed IA, designed in 0.18um CMOS process, consumes 2.6 mW at 1.8V supply and occupies 0.08 mm(2). In the presence of 1% transistor mismatch and 2% parasitic capacitor mismatch, the proposed IA achieves 42dB of gain and 148dB of CMRR using three IAs whose gain and CMRR are 18dB and 72dB respectively.