A method of characterizing a circuit comprises the steps of measuring a first delay associated with the circuit when the circuit is substantially unloaded; measuring a second delay associated with the circuit when the circuit is loaded by a predetermined impedance; determining a difference between the second delay and the first delay, the delay difference corresponding to a switching impedance associated with the circuit; and determining a characterization parameter of the circuit, the characterization parameter being a function of at least the switching impedance associated with the circuit. The methodologies of the present invention are directed primarily to individually evaluating pullup and pulldown delays with substantial precision (e.g., sub-picosecond) for a representative set of circuits in the presence of an arbitrary switching history.