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Adaptive Photoreceptor with Wide Dynamic Range

Delbrück, Tobi and Mead, Carver A. (1994) Adaptive Photoreceptor with Wide Dynamic Range. In: 1994 IEEE International Symposium on Circuits and Systems, 1994. ISCAS '94. Vol.4. IEEE , Piscataway, NJ, pp. 339-342. ISBN 0-7803-1915-X.

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We describe a photoreceptor circuit that can be used in massively parallel analog VLSI silicon chips, in conjunction with other local circuits, to perform initial analog visual information processing. The receptor provides a continuous-time output that has low gain for static signals (including circuit mismatches), and high gain for transient signals that are centered around the adaptation point. The response is logarithmic, which makes the response to a fixed image contrast invariant to absolute light intensity. The 5-transistor receptor can be fabricated in an area of about 70 μm by 70 μm in a 2-μm single-poly CMOS technology. It has a dynamic range of 1-2 decades at a single adaptation level, and a total dynamic range of more than 6 decades. Several technical improvements in the circuit yield an additional 1-2 decades dynamic range over previous designs without sacrificing signal quality. The lower limit of the dynamic range, defined arbitrarily as the illuminance at which the bandwidth of the receptor is 60 Hz, is at approximately 1 lux, which is the border between rod and cone vision and also the limit of current consumer video cameras. The receptor uses an adaptive element that is resistant to excess minority carrier diffusion. The continuous and logarithmic transduction process makes the bandwidth scale with intensity. As a result, the total A.C. RMS receptor noise is constant, independent of intensity. The spectral density of the noise is within a factor of two of pure photon shot noise and varies inversely with intensity. The connection between shot and thermal noise in a system governed by Boltzman statistics is beautifully illustrated.

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Additional Information:© 1994 IEEE. We acknowledge support from the ONR and MOSIS. Rahul Sarpeshkar made a crucial observation about the relationship between shot and thermal noise. Shih-Chii Liu, David Standley, and Dick Lyon provided helpful comments about this work.
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Office of Naval Research (ONR)UNSPECIFIED
Record Number:CaltechAUTHORS:20150113-105738115
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Official Citation:Delbruck, T.; Mead, C.A., "Adaptive photoreceptor with wide dynamic range," Circuits and Systems, 1994. ISCAS '94., 1994 IEEE International Symposium on , vol.4, no., pp.339,342 vol.4, 30 May-2 Jun 1994 doi: 10.1109/ISCAS.1994.409266 URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:53623
Deposited By: Kristin Buxton
Deposited On:13 Jan 2015 19:18
Last Modified:03 Oct 2019 07:51

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