We all know the wide range of possibilities at the variety of diodes for the specific applications, the combination of P and N semiconductor is used to build junction diode, from that transistor comes into the picture, which may utilize semiconductor technology.

But the diode-based electronic didn’t limit to the p-n junction, many varieties are now at diodes. In this post, we are discussing a special type of diode called Trapatt diode.

It is a special type of diode the applications of this trapatt diode are particularly at military communication-based applications, due to the widest characteristics of this electronic device, it is a suspicious electronic component for everyone.

trapatt diode full form

TRApped Plasma Avalanche Triggered Transit mode is the full form of this electronic component.

Construction of Trapatt diode

Construction of Trapatt diode
Construction of Trapatt diode


The construction of the Trapatt diode is similar to the pin diode due to the intermediate layer gap, the diode consists of three-layer P+, N, and N+, but for higher power an N+, P, and P+.

In this post, we explain the first type that is P+, N, and N+ trapatt diode, so the N layer is called our depletion layer.

Trapatt diode working

Trapatt diode working
Trapatt diode working

The above circuit shows the trapatt diode working diagram, at the circuit we can see a square wave generator, so a square pulse is used to trigger the diode.

After the diode start operation, a large amount of charge accumulation has happened at the depletion region at the junction of the trapatt diode.

Then an electrical field at the junction will increase linearly and after some time charge become sufficient, the voltage starts falling.

In that situation, a plasma formation is happened at the diode, at the same time voltage and current decrease continually and the plasma extraction has taken place from at junction region.

Then after charge carriers are completely removed, there will be a voltage increase at the trapatt diode for further diode charging.

At a particular point, the diode becomes fully charged, and then it maintains a constant voltage limit.

Drift current

As like PN junction here at trapatt diode, there will be a drift current formation at the time, when a heavy electrical field is formed at the drift space that is the depletion region, and the electrons and holes are drift out the layer.


Trapatt diode waveform

Trapatt diode waveform
Trapatt diode waveform


The trapatt diode waveform tells us about the working process of the diode at each stage and results.

  • AB – Charging of the trapatt diode junction capacitance
  • BC – Electrons and hole plasma formation by depressed field
  • DE – An plasma extraction happened
  • EF – charger carrier removed
  • FG – Diode again chargers
  • GA – voltage increases again

Trapatt diode avalanche zone velocity formula

    vZ = J/ q. NA

         J = Current density

         q = charge on electron

         NA = Doping concentration

Features of Trapatt diode

  • Operating frequency range = 1 to 3 GHz
  • Working operation = plasma avalanche
  • Output power = 250w at 3GHz

                          550w at 1GHz

  • Efficiency = 35% at 3GHz and 60% at 1GHz
  • Noise figure = very high 60db


Difference between impatt and trapatt diode

When we consider the difference between impatt and trapatt diode, impatt diode utilizes ionization multiplication and at the same time, trapatt works with plasma extraction.

The trapatt diode is also called an upgraded version of the impatt diode, this is because the trapatt diode has a clear upper hand at almost all technical specifications.

Advantage of trapatt diode

  • They had large efficiency at DC to RF signals
  • The operating range frequency starts from MHz to GHz
  • High efficiency than impatt diode
  • Very low power dissipation
  • Suitable for pulsed operation

Disadvantages of trapatt diode

  • High noise figure
  • Upper frequency is limited to below millimeter band
  • They are very sensitive to harmonics

Applications of trapatt diode

  • At pulsed radar as local oscillator
  • At radio altimeters
  • Airborne
  • Microwave oscillator
  • Used in microwave beacons
  • Instrument landing system
  • LO in radar

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