The general diode equation or the non-ideal
diode equation is the foundation of circuit models of active devices for the
past several decades. Apart from the effect of p-n junction, this equation also
accounts for the series bulk resistance of a diode. Despite a reasonable
agreement of the equation with measured IV characteristics, it is shown here that
the equation is incompatible with basic theories of circuits and systems.
Therefore, a modification in the equation is proposed to remove this incompatibility.
This modified equation leads to a compact model of a p-n junction diode that has
an excellent agreement with the measured IV characteristics.