Wide Dynamic Range Image Sensor

Dynamic range expansion method

A Wide Dynamic Range (WDR) CMOS Image Sensor using multiple capture with different exposure time in 1frame period is proposed. A long and three short accumulation time signals are read out in one frame period. The long accumulation (LA) signals occupy three time slots for signal accumulation. Using the time slots for reading the LA signals, the short accumulation (SA) signals are accumulated. The very short accumulation (VSA) and extremely short accumulation (ESA) signals are accumulated using the time slots for reading the SA and VSA signals, respectively. The unit time for one slot is one-sixth of one frame period. If the image sensor operates at 30 frames per second, the unit time is 1/180 s = 5.5 ms. Using this multiple sampling method, a very wide dynamic range image with linear response can be synthesized.

Multiple exposure time signals.

Wide dynamic range image sensor

A very wide dynamic range image sensor which has a linear response for whole illumination range is fabricated based on multiple exposure method. An improved A/D converter enables a large capacitor to be integrated in a given chip area, and digital coupling noise is suppressed by a new operation timing of the ADC, which results in random noise reduction and non-linearity improvement. Measured random noise of the ADC is 363 uVrms in 12-bit, 1 V full-scale. The measured 12-bit differential non-linearity (DNL) is within +0.3 LSB / -0.3 LSB. The dynamic range of the prototype image sensor has been expanded to 153 dB with a linear response by using the technique of extremely short accumulation time signal readout and the improved 12-bit column parallel ADCs.

Chip photograph.	Synthesized image.	DNL plot.

Applications

Automobile, Security camera, industrial applications, and so on.

References

1. M. Mase, S. Kawahito, M. Sasaki, Y. Wakamori, and M. Furuta, " A Wide Dynamic Range CMOS Image Sensor with Multiple Exposure-Time Signal Outputs and 12-bit Column-Parallel cyclic A/D Converters," IEEE Journal of Solid-State Circuits, vol. 40, No. 12, pp. 2787-2795, Dec., 2005
2. J. H. Park, M. Mase, S. Kawahito, M. Sasaki, Y. Wakamori, and Y. Ohta, " A 142dB Dynamic Range CMOS Image Sensor with Multiple Exposure Time Signals,"," Proc. 2005 ASSCC A2L-3, pp. 85-88, Taiwan, Nov. 2005.
3. J. H. Park, S. Kawahito, M. Furuta, M. Sasaki, Y. Wakamori, M. Mase, and Y. Ohta, " A Wide Dynamic Range CMOS Image Sensor with Improved 12-bit Column Parallel Cyclic ADCs," The Journal of the Institute of Image Information and Television Engineers, Vol. 61, No. 3, pp. 360-368, Mar. 2007.