An Ultra-High Frame Rate Ion Imaging Platform Using ISFET Arrays With Real-Time Compression

Abstract

In this paper, a Lab-on-Chip platform with ultra-high throughput and real-time image compression for high speed ion imaging is presented. The sensing front-end comprises of a CMOS ISFET array with sensors biased in velocity saturation for a linear pH-to-current conversion and high spatial and temporal resolution. An array of 128 × 128 pixels is designed with a pixel size of 13.5 μm × 10.5 μm. In-pixel reset switches are applied for offset compensation, by asynchronously resetting the floating gate of the ISFET to a known fixed potential. Additionally, each row of pixels is processed by a current mode signal pipeline with auto zeroing functionality to remove fixed pattern noise, followed by an on-chip 1 MS/s 8-bit row-parallel single slope ADC. Fabricated in standard TSMC 180 nm BCD process, the entire system-on-chip occupies a silicon area of 2 mm × 2 mm, and achieves a frame rate of 6100 fps (7800 fps from simulation). A high speed 25 ms-latency readout platform based on a USB 3.0 interface and standard JPEG is presented for real-time ion imaging and image compression respectively, while an optimised JPEG algorithm is also designed and verified for a higher compression ratio without sacrificing image quality. We demonstrate real-time ion image visualisation by sensing high speed ion diffusion at 6100 fps, which is more than two times faster than the current state-of-the-art.