QLOG - logarithmic CMOS pixel with single electron detection capability

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 signal logarithmic compression and charge transfer based signal readout. This structure gives a linear response at low light condition and logarithmic response at high light condition. The charge transfer readout suppresses efficiently the KTC noise by using a true CDS at low light condition. At high light condition, thanks to charge domain logarithmic compression, it has been demonstrated that 3000 electrons should be enough to cover 120dB dynamic range with a mobile phone camera-like 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 simple single photon detection capability without complex sensor/system design. A first prototype sensor with 320x240 pixels has been implemented to validate this principle. The first results validate the logarithmic charge compression theory and the low readout noise due to charge transfer based readout.