A Low-Power Blocking-Capacitor-Free Charge-Balanced Electrode-Stimulator Chip With Less Than 6 nA DC Error for 1-mA Full-Scale Stimulation

TLDR: An electrode-stimulator chip is described that removes the need for large dc blocking capacitors in neural implants by achieving precise charge-balanced stimulation with <6 nA of dc error, well below the industry's safety limit of 25 nA.

Abstract: Large dc blocking capacitors are a bottleneck in reducing the size and cost of neural implants. We describe an electrode-stimulator chip that removes the need for large dc blocking capacitors in neural implants by achieving precise charge-balanced stimulation with <6 nA of dc error. For cochlear implant patients, this is well below the industry's safety limit of 25 nA. Charge balance is achieved by dynamic current balancing to reduce the mismatch between the positive and negative phases of current to 0.4%, followed by a shorting phase of at least 1 ms between current pulses to further reduce the charge error. On +6 and -9 V rails in a 0.7-mum AMI high voltage process, the power consumption of a single channel of this chip is 47 muW when biasing power is shared by 16 channels.