Determining the Constant PIN Diode Impedance Point for Broadband Reconfigurability

Broadband, high power, fast switching RF control and reconfigurable circuits frequently use PIN diodes as the controlling element. An assumption often made by circuit designers is that the PIN diode resistance is constant over frequency (not considering parasitics). PIN diode impedance is influenced by the junctions and the I-region carrier lifetime (τ) at frequencies as high as several hundred MHz, and so a means to define the onset of the high frequency resistance will provide these designers a guideline for that constant-resistance assumption. This paper provides such a guideline and shows how measurements of PIN diode impedance as a function of frequency can provide this metric, which analysis shows to be approximately 10/πτ. The procedure is validated with measurements on packaged PIN diodes.