A new wide dynamic range CMOS pulse-frequency-modulation digital image sensor with in-pixel variable reference voltage

This paper proposes a new pulse-frequency-modulation (PFM) digital pixel sensor (DPS) with an in-pixel variable reference voltage generator to increase the resolution of the pixel, especially when the level of illumination is low. The proposed PFM DPS offers the attractive characteristics of a reduced integration time when the level of illumination is low, reduced complexity of routing and silicon cost, and comparable fill factor as that of conventional PFM DPS, however, with a significantly improved dynamic range. The proposed digital image sensor is implemented in TSMC-0.18 mum 1.8 V CMOS technology and validated using Spectre with BSIM3V3 device models. Simulation results demonstrate that the PFM digital pixel has a dynamic range of 150 dB when integration time is set to 60 mus, approximately 70 dB more than the conventional PFM digital pixel sensors.

[1]  A. Bermak,et al.  A digital pixel sensor array with programmable dynamic range , 2005, IEEE Transactions on Electron Devices.

[2]  Xinqiao Liu,et al.  A 10000 frames/s CMOS digital pixel sensor , 2001, IEEE J. Solid State Circuits.

[3]  Amine Bermak,et al.  A CMOS Image Sensor using Variable Reference Time Domain Encoding , 2007, 2007 IEEE International Symposium on Circuits and Systems.

[4]  M.F. Snoeij,et al.  Multiple-Ramp Column-Parallel ADC Architectures for CMOS Image Sensors , 2007, IEEE Journal of Solid-State Circuits.

[5]  E. Culurciello,et al.  A biomorphic digital image sensor , 2003, IEEE J. Solid State Circuits.

[6]  S. Kawahito,et al.  A Wide-Dynamic-Range CMOS Image Sensor Based on Multiple Short Exposure-Time Readout With Multiple-Resolution Column-Parallel ADC , 2007, IEEE Sensors Journal.

[7]  Xiuling Wang,et al.  A High Dynamic Range CMOS Image Sensor With Inpixel Light-to-Frequency Conversion , 2006, IEEE Transactions on Electron Devices.

[8]  L. McIlrath.  A low-power low-noise ultrawide-dynamic-range CMOS imager with pixel-parallel A/D conversion , 2001, IEEE J. Solid State Circuits.