Current-Mode ISFET Array with Row-Parallel ADCs for Ultra-High Speed Ion Imaging

2021 IEEE International Symposium on Circuits and Systems (ISCAS)

2021

Self Cite

This paper presents a USB 3.0 based readout platform for real-time ion imaging applications. The front end utilizes an ion-imaging array containing 16 k ISFET pixels to capture ion diffusion at 6100 fps. Operating at 200 MHz, the chip streams ion information at a data rate of 762.94 Mb/s. The backend readout system employs a FIFO-to-USB bridge (FT601Q) that supports Super Speed (5 Gbps) to perform real-time data streaming and operates in bulk transfer mode to ensure data integrity. Implemented on a Xilinx Virtex UltraScale+ FPGA, the system involves a high-throughput data path through the on-board DDR4 SDRAMs, based on which a ring buffer is designed to provide the 2 GB buffering capacity. The readout system can operate in real time regardless of the USB glitches encountered on the Windows OS when involving data polling. In addition, a simple differencing algorithm with threshold detection is integrated into the back end for dynamic frame rate operation. The proposed readout system performs real-time ion imaging at high speed as well as streams the collected images for visualization within a latency of 25 ms, achieving state-of-the-art performance for high-speed Lab-on-Chip applications.

Section: Front-end Cmos Chip With Isfet Arraymentioning

confidence: 99%

A USB 3.0 High Speed Digital Readout System with Dynamic Frame Rate Processing for ISFET Lab-on-Chip Platforms

Kuang

Zeng

2021 IEEE International Symposium on Circuits and Systems (ISCAS)

2021

Self Cite

“…The common-source based readout converts the chemical voltage to current output, then outputs a voltage by discharging the load capacitors [6] Fig. 1[b], or outputs a current via current conveyors [5], [17] Fig. 1[d].…”

Section: Overview Of Isfet Readout Circuitsmentioning

confidence: 99%

“…Moreover, chemical systems already introduce large non-linearity due to double layer, site-bonding models, and crowd ion effect [15]. However, for large-scale systems with high sampling rate, the power consumption of the total sensing arrays can easily exceed mW [17], where a significant resource is required for real time non-linearity correction even when the pH change is small. With a scaled-down sensor size, electrical noise may dominate the noise contribution and affect the linearity due to increased flicker noise and large gate capacitance.…”

Section: Overview Of Isfet Readout Circuitsmentioning

confidence: 99%

Ultrafast Large-Scale Chemical Sensing With CMOS ISFETs: A Level-Crossing Time-Domain Approach

Liu

Constandinou

IEEE Trans. Biomed. Circuits Syst.

2019

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The introduction of large-scale chemical sensing systems in CMOS which integrate millions of ISFET sensors have allowed applications such as DNA sequencing and fine-pixel chemical imaging systems to be realised. Using CMOS ISFETs provides advantages of digitisation directly at the sensor as well as correcting for non-linearity in its response. However, for this to be beneficial and scale, the readout circuits need to have the minimum possible footprint and power consumption. Within this context, this paper analyses an ISFET based pH-to-time readout using an inverter in the time-domain as a level-crossing detector and presents a 32×32 array with in-pixel digitisation for pH sensing. The inverter-based sensing pixel, controlled by a triangular waveform, converts the pH response into a timedomain signal whilst also compensating for sensor offset and thus resulting in an increase in dynamic range. The sensor pixels interface to a 15-bit asynchronous column-wise time-todigital converter (TDC), enabling fast asynchronous conversion whilst using minimal silicon area. Parallel outputs of 32 TDC interfaces are serialised to achieve fast data throughput. This system is implemented in a standard 0.18 µm CMOS technology, with a pixel size of 26 µm × 26 µm and a TDC area of 26 µm × 180 µm. Additionally, we investigate the use of additional offset compensation by having half of the array implemented with the floating gate tied down via a well diode. Measured results demonstrate the system is able to sense reliably with an average pH sensitivity of 30 mV/pH, whilst being able to compensate for sensor offset by up to ±7 V. A resolution of 0.013 pH is achieved and noise measurements show an integrated noise of 0.08 pH within 2-500 Hz and SFDR of 42.6 dB. The total power consumption of the system is measured to be 11.286 mW when operating at a high frame rate of 1 KFPS.

“…(2) Sensitivity -to maximise the surface intrinsic sensitivity as well as maximising the effective sensitivity in circuits through amplification [11], [12]. (3) Readout Speed -to boost the sampling rate of the ISFET in order to monitor high frequency ion interactions [13], [14]. (4) Spatial resolution -scaling the size of the array [15].…”

Section: Introductionmentioning

confidence: 99%

A 1000fps Programmable Gain CMOS ISFET SoC with Array-Level Offset Compensation for Real Time Ion Imaging

Zeng

2021 IEEE International Symposium on Circuits and Systems (ISCAS)

2021

Self Cite

This paper presents a novel Lab-on-Chip ion imaging platform with programmable gain and array-level offset compensation. An array of 128 × 128 ISFET pixels are employed as the sensing front end, followed by a two-step column parallel readout circuit. The offset introduced by trapped charge and drift before any chemical event, is stored and fed back to the programmable gain instrumentation amplifier for compensation and signal amplification. A column-parallel 8-bit single slope ADC and 8-bit R-2R DAC are designed to achieve real-time array-level correlated double sampling, which also enables new possibilities to maximise sensitivity using off-chip image processing techniques. The system operates in real-time at a frame rate of up to 1000 fps, with a maximum effective sensitivity of 1 V / pH. Designed in TSMC 0.18 BCD process, the chip occupies a die area of 2.3 mm × 4.5 mm. We anticipate that this work would become a next generation solution for revealing inperceptible ion interactions in various biomedical applications.