A 128 × 128 Current-Mode Ultra-High Frame Rate ISFET Array with In-Pixel Calibration for Real-Time Ion Imaging

An ultra-high frame rate and high resolution ion-sensing Lab-on-Chip platform using a 128x128 CMOS ISFETarray is presented. Current mode operation is employed to facilitate high-speed operation, with the ISFET sensors biased in the triode region to provide a linear response. Sensing pixels include a reset switch to allow in pixel-calibration for nonidealities such as offset, trapped charge and drift by periodically resetting the floating gate of the ISFET sensor. Current mode row-parallel signal processing is applied throughout the readout pipeline including auto-zeroing circuits for the removal of fixed pattern noise. The 128 readout signals are multiplexed to eight high-sample-rate on-chip current mode ADCs followed by an off-chip PCIe-based digital readout system on a FPGA with a latency of 0.15s. Designed in a 0.35 um CMOS process, the complete system-on-chip occupies an area of 2.6mm x 2.2mm and the whole system achieves a frame rate of 3000fps which is the highest reported in the literature. The platform is demonstrated for real-time ion-imaging through the high-speed visualisation of sodium hydroxide (NaOH) diffusion in water. Furthermore, the proposed platform is able to achieve real-time visualisation of ion dynamics on a screen at 60fps in addition to slow-motion replay in 3000fps.