# A Bio-Inspired Analog Silicon Retina with Michaelis-Menten Auto-Adaptive Pixels Sensitive to Small and Large Changes in Light

• Mafrica Stefano
• Godiot Stéphanie
• Menouni Mohsine
• Boyron Marc
• Expert Fabien
• Juston Raphaël
• Marchand Nicolas
• Ruffier Franck
• Viollet Stéphane
ART

In this paper, we present: (i) a novel analog silicon retina featuring auto-adaptive pixels that obey the Michaelis-Menten law, i.e. $V=V_m I^n/(I^n+\sigma^n)$; (ii) a method of characterizing silicon retinas, which makes it possible to accurately assess the pixels’ response to transient luminous changes in a ±3-decade range, as well as changes in the initial steady-state intensity in a 7-decade Range. The novel pixel, called M2APix, which stands for Michaelis-Menten Auto-Adaptive Pixel, can auto-adapt in a 7-decade range and responds appropriately to step changes up to ±3 decades in size without causing any saturation of the Very Large Scale Integration (VLSI) transistors. Thanks to the intrinsic properties of the Michaelis-Menten equation, the pixel output always remains within a constant limited voltage range. The range of the Analog to Digital Converter (ADC) was therefore adjusted so as to obtain an LSB voltage of 2.35 mV and a full-scale resolution of 9-10 bits. The results presented here show that the M2APix produced a quasi-linear contrast response once it had adapted to the average luminosity. Contrary to what occurs in its biological counterparts, neither the sensitivity to changes in light nor the contrast response of the M2APix depend on the mean luminosity (i.e. the ambient lighting conditions).