The Optical Mouse: Early Biomimetic Embedded Vision - Advances in Embedded Computer Vision - page 10

Fig. 1.10 The “Ready” and “Done” signals from an imaging array with lateral inhibition, such as
that in Fig. 1.8 , cooperate with this nonoverlapping-clock generation circuit to yield a free-running
self-timed imaging system. The synchronous digital logic parts of the system use the two-phase
nonoverlapping clocking methodology that we were teaching for digital system design as part of
the Mead-Conway VLSI design revolution [ 30 ]. The duration of the “long” clock phase would be
whatever time was needed for the imager to reach a stable binary state—faster at high light levels,
slower at low light levels
found in real retinas, involving horizontal cells and amacrine cells [ 11 ], and in silicon
retinas [ 13 ].
1.4 Metastability
The ability of the Hopfield network to fall into a stable state depends on positive
feedback. A multi-stable system also has metastable states, or saddle points, where
it can hang for a long time before deciding which side to fall toward. The mouse's