TABLE OF CONTENTS A straight isolated 22 AWG wire has an inductance of approximately 20 nH per inch of length. The inductance increases with smaller diameter wire. Grover [3] gives formulas for the inductance of various isolated conductors.
Conductors are generally placed in the vicinity of ground or other conductors, which lowers the effective inductance. For example, the 22 AWG wire has an inductance of approximately 26 nH when placed 1 inch above a ground plane, 19 nH at 0.2 inch spacing, and 12 nH when placed on top of 0.062 inch thick PWB with a ground plane. The effective inductance is more accurately predicted using transmission line concepts discussed later in this chapter. Appropriate transmission line models include a wire over ground, wire in a trough, wire between ground planes and others.
The 20 nH per inch approximation is suitable for estimating the additional inductance of leads on inductors or the parasitic lead inductance of capacitors and other components.
