QLog Solar-Cell Mode Photodiode Logarithmic CMOS Pixel Using Charge Compression and Readout.

Yang Ni

doi:10.3390/s18020584

Abstract

In this paper, we present a new logarithmic pixel design currently under development at New Imaging Technologies SA (NIT). This new logarithmic pixel design uses charge domain logarithmic signal compression and charge-transfer-based signal readout. This structure gives a linear response in low light conditions and logarithmic response in high light conditions. The charge transfer readout efficiently suppresses the reset (KTC) noise by using true correlated double sampling (CDS) in low light conditions. In high light conditions, thanks to charge domain logarithmic compression, it has been demonstrated that 3000 electrons should be enough to cover a 120 dB dynamic range with a mobile phone camera-like signal-to-noise ratio (SNR) over the whole dynamic range. This low electron count permits the use of ultra-small floating diffusion capacitance (sub-fF) without charge overflow. The resulting large conversion gain permits a single photon detection capability with a wide dynamic range without a complex sensor/system design. A first prototype sensor with 320 × 240 pixels has been implemented to validate this charge domain logarithmic pixel concept and modeling. The first experimental results validate the logarithmic charge compression theory and the low readout noise due to the charge-transfer-based readout.

Highlights

Silicon-based low light level image sensors are critical for many low-power, low-cost, and highly integrated vision systems
Logarithmic response pixel is interesting for such applications since it can produce a very wide dynamic range directly at the pixel level without exposure accommodation or any image processing
Of this paper, we will focus on the basic logarithmic charge compression from a test chip with 320 × 240 QLog pixels in order to validate the theoretical model and check the and introduce a theoretical model based on the electron evaporation phenomenon from a potential response across the pixelsand in an array. time on the response curve of the QLog pixel will be well. uniformity

Summary

Introduction

Silicon-based low light level image sensors are critical for many low-power, low-cost, and highly integrated vision systems. QLog pixel the canlogarithmic be an elegant solution to the suppression of KTC in low light high light conditions, compression overcome the too-low integration well capacity in actual high-sensitivity, subelectron readout at the charge collection period considerably reduces the total electron number required to cover a widenoise dynamic range. The QLog pixel has the same conceptual structure as a conventional 4T pixel with buried fully accumulated and a large dark current and nonuniformity will be generated, which considerably photodiode and charge-transfer-based readout. Of this paper, we will focus on the basic logarithmic charge compression from a test chip with 320 × 240 QLog pixels in order to validate the theoretical model and check the and introduce a theoretical model based on the electron evaporation phenomenon from a potential response across the pixelsand in an array.

Numeric solution

Prototype Test Chip and Measurement Results

50 Hz with

Findings

Conclusions