Thirty Two-Stage CMOS TDI Image Sensor With On-Chip Analog Accumulator

Abstract

This brief presents a 32-stage CMOS time delay integration image sensor with on-chip column parallel analog accumulator. Temporal oversampling technique is applied in the sensor to realize synchronous signal capturing. A column parallel analog accumulator with layout size of 0.09 mm 2 is integrated at both sides of pixel array. Through adopting input-offset storing technique, a column fixed pattern noise because of the amplifier's offset variations is reduced by the accumulator. The accumulator also acts as a pixel noise canceller. The fabricated chip in 0.18-μm one-poly four-metal 1.8/3.3-V CMOS technology achieves the maximum line rate of 3875 lines/s. The measured signal-to-noise ratio of the fabricated sensor is improved on average by 11.9 dB at 16 stages and 14.2 dB at 32 stages. The presented sensor is suitable for application in low illumination, high scanning speed, and remote sensing systems. Index Terms-Analog accumulator, CMOS image sensors, readout circuits, signal-to-noise ratio (SNR), time delay integration (TDI). 1063-8210

A Low Power Digital Accumulation Technique for Digital-Domain CMOS TDI Image Sensor

“…Additionally, due to the incompatibility with the CMOS process, the CCD could not integrate with other functions on the same chip with the sensor [4]. In recent years, TDI image sensors implemented with the CMOS process have been reported [5,6,7,8,9,10,11,12,13,14]. Compared with the CCD, CMOS TDI image sensors could successfully integrate various analog and digital circuits as an on-chip camera [4].…”

“…There are typically three kinds of accumulation methods: charge-domain accumulation scheme [5,6,7,8], analog-domain accumulation scheme [9,10,11] and digital domain accumulation scheme [12,13,14] for CMOS TDI image sensors. In the charge-domain accumulation scheme, the noiseless accumulation enables good SNR.…”

“…However, the charge transfer efficiency and full well capacity, which strongly depend on process, limit its momentum of development [6,7]. With respect to the analog-domain accumulation scheme, the generated signals from pixels are firstly accumulated by the analog accumulator, and then the accumulated result is quantized by column analog-to-digital converter (ADC) [9,10]. Because the maximum accumulated voltage depends on the supply voltage, the dynamic range of the analog-domain CMOS TDI image sensor is limited by the supply voltage [9,10].…”

“…With respect to the analog-domain accumulation scheme, the generated signals from pixels are firstly accumulated by the analog accumulator, and then the accumulated result is quantized by column analog-to-digital converter (ADC) [9,10]. Because the maximum accumulated voltage depends on the supply voltage, the dynamic range of the analog-domain CMOS TDI image sensor is limited by the supply voltage [9,10]. Since the analog memory cell of the analog accumulator is implemented with capacitors, the accumulator area is considerably large [9,10].…”

“…Because the maximum accumulated voltage depends on the supply voltage, the dynamic range of the analog-domain CMOS TDI image sensor is limited by the supply voltage [9,10]. Since the analog memory cell of the analog accumulator is implemented with capacitors, the accumulator area is considerably large [9,10]. In the digital domain accumulation scheme, the outputs of pixels are firstly quantized by column ADC, and then the corresponding digital results are added together by the digital accumulator [14].…”