The Optical Mouse: Early Biomimetic Embedded Vision - Advances in Embedded Computer Vision - page 12

Fig. 1.12 Chaney and Molnar showed in 1973 that a pair of cross-coupled TTL NAND gates had
an oscillatory metastable state
Fig. 1.13 Chaney and
Rosenberger showed, at the
1979 Caltech Conference on
VLSI, that cross-coupled
nMOS NOR gates would exit
the metastable point via a
simple exponential
divergence
our thinking about system timing, as described in Chuck Seitz's chapter in the Mead-
Conway topic [ 33 ]. In my initial report, I credited Seitz for the done-detection idea:
Note that we do not use the inhibition NOR gate output itself for done-detection, but a
buffered version of it after a high threshold buffer (inverter pair); this is the easiest way to
prevent false done-detection during a metastable condition (Seitz 1980). The buffered signal
is not used for inhibition, since that would make it participate in the metastable condition,
and because the extra delay would cause oscillatory metastable states.
Chaney and Rosenberger had shown that the metastable state of a pair of cross-
coupled nMOS NOR gates, like that of the two-pixel imager of Fig. 1.7 , would be
a simple unstable equilibrium, which would diverge exponentially toward a stable
state, without oscillation [ 8 ]; Fig. 1.13 shows their model and analysis from the 1979
Caltech Conference on VLSI. This was the behavior I needed, and I had reasoned