Temperature Compensated Logarithmic Amplifier for CMOS Image Sensor

Seunghyun Oh, Yonghyun Shim, Young Jun Song

Abstract

The natural sensors such as human organism show the logarithmic sensibility. That is, it is more sensible in the lower level signal, and the sensibility weakens as the intensity goes up. An image sensor incorporating the logarithmic pixel can achieve more recognizable image to human eyes and extend the dynamic range of input signal with signal compression.

In this project, a logarithmic amplifier for CMOS image sensor employing the exponential V-I relationship of the subthreshold region is presented. Due to the strong dependence on temperature in the subthreshold current, it is essential to compensate the temperature variation. This amplifier includes the sensing stage from a photodiode, the logarithmic amplifier stage, and the temperature compensation stage.

The dimension of this amplifier will fit in one pixel size, and the logarithmic response will be within +/-2 dB variation at the temperature range of 0C ~ 75C. The dynamic range will be more than 50 dB.

References

  1. Storm, G.; Henderson, R.; Hurwitz, J.E.D.; Renshaw, D.; Findlater, K.; Purcell, M., "Extended Dynamic Range From a Combined Linear-Logarithmic CMOS Image Sensor," Solid-State Circuits, IEEE Journal of , vol.41, no.9, pp. 2095-2106, Sept. 2006
  2. Dillard, W.C., "A high-voltage temperature compensated logarithmic amplifier suitable for integration in a BiCMOS power controller IC," Applied Power Electronics Conference and Exposition, 2004. APEC '04. Nineteenth Annual IEEE , vol.1, no., pp. 258-263 Vol.1, 2004
  3. Ji-Jon Sit, Sarpeshkar, R., "A micropower logarithmic A/D with offset and temperature compensation," Solid-State Circuits, IEEE Journal of , vol.39, no.2, pp. 308-319, Feb. 2004

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