A 140-dB CMRR Low-noise Instrumentation Amplifier for Neural Signal Sensing

This paper presents a novel IA (instrumentation amplifier) design for implantable biomedical devices and systems with a 140-dB CMRR (common-mode rejection ratio). The proposed IA is composed of 3 stages, including a preamplifier, a 2nd-order BPF (band-pass filer), and a DC-level shifter and output buffer stage. A low-noise gm-C amplifier is used in the preamplifier stage so as to reduce the coupled thermal noise which might overwhelm the weak neural signals. The BPF is designed based on an OTA (operational transconductance amplifier) with dual current switches aiming at the low power as well as low noise demands. A source follower is employed to carry out the DC-level shifter and the output buffer, which provides an output signal adequate to drive the following stage, which is usually an ADC (analog to digital converter). Detailed analysis of the proposed circuitry is derived to solidify the proposed architecture. The proposed design is implemented using TSMC 0.35 mum 2P4M CMOS process. The results of post-layout simulations verify the performance of our design. The CMRR is better than 140 dB, and, most important of all, the input noise (RMS) is merely 23.28 dB at all PVT (process, supply voltage, temperature) corners