A novel multichannel analog-to-time converter based on a multiplexed sigma delta converter

In this paper, a new sigma delta modulator based on a multiplexed input topology is proposed to decrease power consumption and size in implantable bio-interfacing systems. An opamp sharing technique is employed in order to process several input sequentially. The proposed sigma delta modulator integrates each input separately and stores the integrated value inside a dedicated capacitor. We show that the resulting transfer function of the modulator is equivalent for all channels. The proposed circuit has been implemented in a 180-nm TSMC process. The circuit includes 4 channels and consumes 11.5 μW per channel, provides an ENOB of 7.8 bits, and presents a bandwidth of 10 kHz. The chip area for the proposed design is 150 μm × 135 μm for 4 multiplexed inputs.