This vision chips is one of the examples of multifunctional vision chips, in which several tasks are performed within the chip. The core of the chip is composed of a 2D array of Andreou-Boahen's retina cells [Boahen and Andreou 92, Andreou and Boahen 94b]. Two one-dimensional motion detection and two one-dimensional centroid computation arrays bear the computation task of the chip. The motion detection is performed by the circuit introduced in section 3.9. Centroid computation is done using DeWeerth's architecture in section 2.16. The motion and centroid function are performed only on the central row and column of the retina array. This is done by sampling the central row and column and holding them in a sample & hold circuit described in [Vittoz et al. 91]. As the Andreou-Boahen's retina intrinsically removes the centroid information, an offset is added to the output of the retina before applying it to the centroid computation circuit. The architecture of the chip is shown in Figure 3.30.
The chip has been targeted for sun-tracking in high-altitude balloons. The shape of the sun and its high contrast with the dark sky in an altitude of 35 Km prevents complications due to low contrast or multiple arbitrary shape objects. In fact this chip is an excellent example of very small size custom vision chip for a constrained vision task, which would have otherwise required a large hardware with at least ten times the size and power dissipation.
The 50 
50 retina array and the accompanying motion and centroid
computation circuits occupy an area of 6.8mm 6.9mm in a
standard 2 
m CMOS process. The computational core dissipates
17.5 mW.
Figure: Architecture of Meitzler et al.'s position and motion computation vision chip.