Applications of PIN Diodes - App Note

The most important property of the PIN diode is the fact that it can, under certain circumstances, behave as an almost pure resistance at RF frequencies, with a resistance value that can be varied over a range of approximately 1 O to 10 KO through the use of a DC or low frequency control current. When the control current is varied continuously, the PIN diode is useful for leveling and amplitude modulating an RF signal. When the control current is switched "on" and "off" or in discrete steps, the device is useful for switching, pulse modulating, attenuating, and phase shifting of an RF signal. In addition, the PlN's small size, weight, high switching speed, and minimized parasitic elements make it ideally suited for use in miniature, broadband RF signal control components. A PIN diode is a silicon semiconductor consisting of a layer of intrinsic (high resistivity) material of finite area and thickness which is contained between highly doped p and n type material. When the diode is forward biased, charge is injected into the intrinsic or "I" region. This charge consists of holes and electrons which have a finite lifetime before recombination. The density of charge in the intrinsic region and its geometry determines the conductance of the device, while the lifetime [denoted by t (tau)] determines the approximate low frequency limit of useful application.