A 97 dB-CMRR Gm-Controlled Inverter-Based Amplifier Employing Multi-CMFB Loops for Multi-Channel Bio-Signal Recording

This article presents a Gm-controlled inverter (GC-INV) based amplifier with multiple common-mode feedback (CMFB) loops for multi-channel bio-signal recording. The GC-INV forms a DC-coupled input to ensure a high input impedance. The multi-CMFB, including twin local (TL), regional system (RS), and averaged system (AS) CMFB loops, is introduced through the paralleled GC terminals to provide multiple feedback paths. The TL-CMFB with capacitor-reused topology not only reduces the die area and increases the differential-mode gain, but also reduces the common-mode (CM) gain. The RS-CMFB mitigates the common-mode interference (CMI) due to the mismatch of the CM feedback paths. The AS-CMFB further mitigates the accumulated CMI from CM sampling paths. These CMFB loops avoid the design trade-off between the intrinsic CMRR and the efficiency of area and power. The proposed GC-INV based amplifier with multi-CMFB is fabricated in a 0.18- μ m CMOS technology. It achieves an intrinsic CMRR of 97 dB, TCMRR of 78 dB, and the single-channel INV consumes a chip area of 0.008 mm2.