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Physiologist's Friend Chip design

The Physiologist's Friend Chip is a tool for educators and physiologists that electronically models the early visual system. This page holds the design of the friend23 chip, which is the most recent design dated 2001.

Layout of friend23

Layout of the Friend23 design. Die size is 2.2×2.2 mm and the photodiode sizes are about 163um wide and 190um high.



The PhysioFriend chip was designed by members of the Inst. of Neuroinformatics, including Elissabetta Chicca, Simon Bovet, Tobi Delbruck, Shih-Chii Liu, Giacomo Indiveri, and others.


We provide this design as a contribution to the neuromorphic engineering community. By using these design resources, you agree to the following terms: These designs are distributed under the terms of the GNU Public License ( - TOCGPL), with the following additions:

  1. You are responsible for any use of these resources that infringe on existing patents. (We are not aware of any such existing IP.)
  2. We have built these circuits on several chips and they function correctly, but chip design is a tricky business, so there is absolutely no warranty as to functionality of these circuits.
  3. Use of these resources on chips that result in publications or for use in courses on electronic design must cite our relevant publications and must acknowledge the Institute of Neuroinformatics . For this chip, the publication is

T. Delbruck, S.C. Liu. (2004). A silicon visual system as a model animal. Vision Research, vol. 44, issue 17, pp. 2083-2089