A Differential Difference Amplifier With A Combined Input Pairs for Neural Signal Recordings

This paper presents a differential difference amplifier (DDA) with a combined symmetrical and complementary input pairs for neural signal recording. The front-end amplifier determines the fidelity, signal-to-noise ratio, power consumption and form size for the future multi-channel neural signal recording systems and applications. The proposed DDA has three input transconductors, the first one is connected to the target neural signal, to ensure a high input impedance. The second one stabilizes the dc quiescent point and determines the cut-off frequency. The third one provides the common mode feedback (CMFB) and gain calibration. The circuits are targeted at IC realization, designed in a 0.18-μm CMOS technology. The post layout simulation achieves an input impedance of circa 1GΩ at 100 Hz, a CMRR of 128 dB. The proposed CIP-DDA (two channels) with a system CMFB achieves a die area of 0.23 mm ² and consumes a power consumption of 51 μW (single channel of DDA consumes 3.6μW).