A wide dynamic range CMOS image sensor with pulse-frequency-modulation and in-pixel amplification

This paper briefly examines the pros and cons of CMOS pulse-frequency-modulation (PFM) digital pixel sensors. A pulse-frequency-modulation digital pixel sensor with in-pixel amplification is proposed to improve the resolution of the pixel sensor at low illumination. The proposed PFM digital pixel sensor offers the characteristics of a reduced integration time when the level of illumination is low with the fill factor comparable to that of PFM digital pixel sensors without in-pixel amplification. The proposed digital image sensor has been designed in TSMC- 1.8 V CMOS technology and validated using Spectre from Cadence Design Systems with BSIM3V3 device models. Simulation results demonstrate that the dynamic range of the proposed PFM digital pixel sensor with in-pixel amplification is 20 dB larger as compared with that of PFM digital pixel sensors without in-pixel amplification. The increased dynamic range is obtained in the low illumination condition where PFM digital pixel sensors without in-pixel amplification cease the operation due to the low photo current.