A High TCMRR, Inherently Charge Balanced Bidirectional Front-End for Multichannel Closed-Loop Neuromodulation

This paper describes a multichannel bidirectional front-end for implantable closed-loop neuromodulation. Stimulation artefacts are reduced by way of a 4-channel H-bridge current source sharing stimulator front-end that minimizes residual charge drops in the electrodes via topology-inherent charge balancing. A 4-channel chopper front-end is capable of multichannel recording in the presence of artefacts as a result of its high total common-mode rejection ratio (TCMRR) that accounts for CMRR degradation due to electrode mismatch. Experimental verification of a prototype fabricated in a standard 180 nm process shows a stimulator front-end with 0.059% charge balance and 0.275 nA DC current error. The recording front-end consumes 3.24 μW, tolerates common-mode interference up to 1 Vpp and shows a TCMRR > 66 dB for 500 mVpp inputs.