The digital and gate is an n-input, single-output and gate which produces an
active 1 value if, and only if, all of its inputs are also 1 values. If any
of the inputs is a 0; the output will also he a 0; if neither of these
conditions holds, the output will be unknown. The delays associated with an
output rise and those associated with an output fall may be specified
independently. The model also posts an input load value (in farads) based on
the parameter input_load. The output of this model does NOT, however,
respond to the total loading it sees on its output; it will always drive the
output strongly with the specified delays.