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In the conditions mentioned above, a first prototype circuit (128 pixels) has been designed and submitted to 
fabrication in a 2.4um CMOS standard process. First hand experience shows that pixel dimensions can be reduced to 
16umx16pm in a 1um CMOS technology. Because of the high speed (5 MHz non-overlapping clock) of the Gaussian 
filter, tested on the previous chip [4], we expect a processing rate of 2.56ms for an 256x256 image. To our knowledge, 
this datum gives the best stereofusion throughput at good illumination conditions. This gives us the possibility to 
envision a temporal averaging process without loosing real-time aspects. 
The 2D prototype have to realize a linear conversion of the light-generated pixel charge in the active matrix area 
into voltage in the read-out stage [5]. The main problem with this is the parasitic capacitance of each column bus, 
which is often bigger than the pixel one. A charge amplifier module between the photodiode matrix and the Gaussian 
filter is needed on each chip in order to minimize those effects. A second prototype circuit ( 64x64 pixel matrix) has 
been designed and submitted to fabrication in a {um CMOS standard process. 
5. CONCLUSIONS 
This paper presents an obstacle-detection tailored stereovision algorithm and its associated analog VLSI 
implementation architecture. Our investigation shows the possibility to realize fast, dense and low-cost CMOS 
monolithic stereovision sensors for the navigation-based applications. 
ACKNOWLEDGEMENTS 
This work is supported by GIE P.S.A. Peugeot Citroen. 
REFERENCES 
[1] Marr D., T. Poggio, 1979 "A Theory of Human Stereo Vision" Proc. Roy. Soc.London, Vol.B204 
[2] Enkelmann & al., 1988 "An Experimental Investigation of Estimation Approaches for Optical Flow Fields" 
in Motion Understanding - Robot and Human Vision, edited by W.N. Martin , J.K. Aggarwal, 
Kluwer Academic Press 
[3] Marr D., E. Hildreth, 1980 "Theory of Edge Detection" Proc. Hoy. Soc. London, Vol.B207 
[4] Ni, Y., B. Arion, F. Devos, 1993 "Yet Another Gaussian Convolver" Proc. 1993 IEEE International 
Symposium on Circuits and Systems, ISCAS'93 Chicago 
[5] Jansson, C., P. Ingelhag, C. Svenson, R. Forchheimer, 1993 "An Adressable 256x256 Photodiode Image 
Sensor Array with an 8-bit Digital Output" , Analog Integrated Circuits and Signal Processing, 
Vol4, No 1, pp 37-49 
IAPRS, Vol.-30, Part 5W1, ISPRS Intercommision Workshop "From Pixels to Sequences", Zurich, March 22-24, 1995