RF and Microwave Diodes

 

We will describe here most important of these:

Varactor Diodes: A varicap diode or varactor diode is a type of diode which has a variable capacitance that is a function of the reverse voltage impressed on its terminals. This property of varying the diode capacitance is useful in tuning circuits, Automatic Frequency Control (AFC) circuits, Antenna tuning, etc.

PIN Diodes (Positive Intrinsic Negative): PIN diode is a semiconductor device that operates as a variable resistor at RF and Microwave frequencies. It can also be used as a switch and Limiter. The variable resistor property makes it usable as an Attenuator.

Step Recovery Diode (SRD): The term step recovery relates to the form of the reverse recovery characteristic of these devices. After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). SRDs can therefore provide very fast voltage transitions by the very sudden disappearance of the charge carriers.

Gunn Diodes: These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of negative differential resistance. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built. Thus GUNN diodes can be used as oscillators.

Parametric Amplifier Diodes: Parametric amplifier diodes are similar to varactor diodes. Here, the parametric variation (reactance variation with the voltage) is made use of to amplify RF signals. A rectangular wave called ‘pumping signal’ is applied to the diode to vary the reactance. This signal frequency is selected such that it is twice the frequency of the signal to be amplified.

Tunnel Diodes: These have a region of operation showing negative resistance caused by quantum tunneling, allowing amplification of signals and very simple bistable circuits. Due to the high carrier concentration, tunnel diodes are very fast, may be used at low (mK) temperatures, high magnetic fields, and in high radiation environments. Because of these properties, they are often used in spacecraft.

For Details:
http://en.wikipedia.org
RF and Microwave Diodes - An Introduction by Anoop N. K. (http://www.avtechpulse.com/faq.html/IV.28/uwdiode.pdf)