PIN DIODE

PIN DIODE

A PIN diode is a type of photodiode that finds use in applications that require high switching speeds. It is made of a high resistance (intrinsic) material that is placed between two doped layers (p and n). Since the combination is p material, intrinsic resistivity material and n material, it is called PIN diode.

How it works:

The device functions in forward or reverse biased modes. When forward biased, it injects a charge into the resistivity layer. The amount of voltage that is given decides the amount of charge and its conductivity. When reverse biased, the device shows high resistivity.

For RF signals, if the control current is changed frequently, the device can level and modulate the amplitude. On the other hand it can be used for pulse modulation and shifting when the control current is switched on and off.

PIN Diode Selection:

PIN diodes are classified as per application: RF switches, RF attenuator, RF modulators, RF phase shifters, wireless communication system, HF band industrial applications, and magnetic resonance. They are sold as glass-packaged, GaAs type, microwave, and surface mount PIN diodes.

The following factors are useful in selection:

Capacitance: Measured as the amount of voltage stored for a fixed charge. Measured in Farad.
RF range: The radio frequency range in MHz that the device can switch.
Resistivity: The resistance to the flow of current measured in ohmmeter.
Other parameters are voltage rating, bandwidth, operating temperature, power dissipation and thermal resistance, chip dimension, etc. of the PIN diode.

Applications:

PIN diodes are used for switching of radio frequency signals (RF).
They are also used in broadband reflective SPST switches and attenuators, resonant SPST switches, multiple diode and multi-throw switches and attenuators, constant impedance switches and attenuators, S-band single/double hybrid coupled PIN attenuator.
They are used in a variety of phase shifters like: cascaded hybrid coupled phase shifter, circulator coupled phase shifter and periodically loaded line phase shifter.
Devices like RF duplexers, digital phase shifters and time multiplex filters find them useful.