The digital 'sop' gate is an n-input, single-output gate which provide
common logic functions by OR gating the outputs of two AND functions. 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.