PIN DIODE

A 'PIN diode' is a diode with a wide, undoped intrinsic semiconductor region between p-type semiconductor and n-type semiconductor regions.
A PIN diode obeys the standard diode equation only for very slow signals. At higher frequencies, the diode looks like an almost perfect (very linear, even for large signals) resistor. The high-frequency resistance is inversely proportional to the DC bias current through the diode. A PIN diode, suitably biased, therefore acts as a variable resistor. This high-frequency resistance may vary over a wide range (from 0.1 ohm to 10K ohm in some cases[1]; the useful range is smaller, though).
This makes PIN diodes useful as microwave and RF switches and attenuators. By changing the bias current through a PIN diode, it's possible to quickly change the RF resistance.
In a PIN diode, the depletion region exists almost completely within the intrinsic region. This depletion region is much larger than in a PN diode, and almost constant-size, independent of the reverse bias applied to the diode. This increases the area where electron-hole pairs can be generated. For these reasons many photodetector devices include at least one PIN diode in their construction, for example PIN photodiodes and phototransistors (in which the base-collector junction is a PIN diode).

Contents

Examples

Examples

SFH203 or BPW43 are cheap general purpose PIN diodes in 5 mm clear plastic case with bandwidth over
100 MHz. They are used in RONJA telecommunication systems. Other more specialized
PIN diodes are used in fiber optic network cards and switches. In this case, the PIN diodes are used as photodiodes.
Also, PIN diodes are very useful in RF applications, as variable resistors. This is useful in applications including MR instrumentation, to drive the RF coil circuits.