Introduction
Discrete, low-cost, surface mount semiconductor diodes are attractive choices for UHF and microwave applications where package parasitic may have a significant impact on performance. The most common package styles are the SOT-23 and the SOD-323 (Figure 1) which were neither designed nor intended for RF service. A primary limitation to their high-frequency performance, particularly in PIN diode shunt connected switches, is parasitic package inductance, which limits high-frequency isolation. The model information available from vendors of these devices has been generally limited to estimates of inductance, typically 1.5 nH, for single junction SOT-23 diodes. Establishing a better model will enable circuit designers to better predict performance and possibly give the manufacturer alternative designs to reduce package parasitic effects.