A CT DSM with DAC Scaling Technique for Direct Neural Recording Front-End

Closed-loop neural detection systems pose significant design challenges to neural recording interface circuits. The interface needs to satisfy the required resolution and power budget while meeting the requirements (e.g. DC offset removal, high DC impedance, stimulation artifacts tolerance, etc.) posed by implantable biomedical scenarios. The state-of-the-art analog-to-digital converter (ADC) direct interface employs a delta-sigma modulator (DSM) structure, where a digital integrator (accumulator) is intentionally relocated behind the quantizer to remove the electrode DC offset. However, the power and area consumptions of the multi-bit digital-to-analog converter (DAC) is increased by the accumulator. Based on the DSM architecture with DC offset removal, this paper proposes a DAC scaling technique to decrease the signal amplitude appearing at the DAC input. It results in the significant reduction in the number of required DAC unit cells and therefore the power and area consumptions of DAC. Meanwhile, to obtain high DC input impedance and high linear input-range, we present circuitry design considerations for the first integrator as well as the feedback loop. Finally, behavioral-level simulation results confirm the efficacy of the proposed structure.