A Low-Power, High CMRR Neural Amplifier System Employing CMOS Inverter-Based OTAs With CMFB Through Supply Rails

Multichannel neural amplifiers are commonly implemented with a shared reference whose input impedance is several times lower than that of the corresponding signal inputs. This huge impedance mismatch significantly degrades the total common mode rejection ratio (TCMRR) regardless of the amplifier's intrinsic CMRR (ICMRR). This study reports a multichannel neural amplifier system that eliminates this impedance mismatch problem by using single-ended CMOS-inverter-based preamplifiers for both the reference and signal inputs. A common-mode feedback (CMFB) loop through the supply rails of the preamplifiers is implemented to enhance their ac input common mode range to 220 mVpp and their ICMRR to more than 90 dB at low frequencies. The ICMRR is maintained above 80 dB up to 1 kHz by minimizing the load drive mismatch between the signal and reference preamplifiers. Implemented in a CMOS 65 nm process, this 16-channel amplifier system operates at 1 V and consumes 118 μW. It has input referred noise of 4.13 μVrms, leading to a noise efficiency factor (NEF) and a power efficiency factor (PEF) of 3.19 and 10.17, respectively. In vivo recordings of cortical neurons of a macaque were successfully acquired, demonstrating the ability of the amplifier to acquire neural signals in an unshielded environment.