In this article we are explaining about Impatt diode, these kinds of diodes are not like our conventional diode. Compare Impatt diode with normal diodes, they are way much more specific to their applications.

What is Impatt Diode?

The Impatt diode is a very high-power semiconductor device that also can handle microwave frequency, the technical operations and applications of this diode are more different from general-purpose diodes. The Impatt diodes have very specific applications at high power devices such as radars at communication systems.

Impatt diode full form

IMPact ionization Avalanche Transit Time diode is the full form of this semiconductor device.

Impatt diode construction

Impatt diode construction
Impatt diode construction

 

The construction of the Impatt diode is somewhat similar to the pin diode because of the presence of an intrinsic layer at the middle of the device.

The semiconductor layer arrangement of the Impatt diode is shown in the figure, first P, N, Intrinsic layer and N-type layer, the gallium arsenide GaAs is used to build the Impatt diode due to low noise behavior of this material.

The Impatt diode structure is designed to works with the reverse-biased operation, the avalanche multiplications process occurs within the high field region.

At this structure a Schottky barrier format is used as the injection junction, the thin layer is main for the high-frequency operation.

Impatt diode symbol

The symbolic indication of the Impatt diode is always a mystery for everyone, but the fact is that they have the normal p-n junction diode symbol.

Impatt diode diagram

Impatt diode diagram
Impatt diode diagram

 

The Impatt diode diagram put forward more information’s about the device, the purposes such as avalanche breakdown will happen at avalanche region and drift current flow due to the electric field is happened at drift region.

 

Working of Impatt diode

We early mentioned that the Impatt diode operation has happened at the reverse biased condition, also called avalanche breakdown condition.

Before we start to explain the working of this device, this may operate at a high voltage value gradient that is about 400kv/cm

At the reverse biased condition current increases gradually, which results in avalanche breakdown, and at reverse condition width of the depletion region increases that is an intrinsic layer.

And at the junction majority of carriers drift out at the drift region, this is because of the presence of the high electric field.

On the condition that charged carriers move with super-fast velocity, the charged carriers collide with each other with other atoms. And this results in forming electron-hole pairs, this is called the avalanche multiplication process of the Impatt diode.

So the moving charged carriers generate a heavy current inside the diode, which is also called impact ionization condition.

Impatt diode characteristics

Impatt diode characteristics
Impatt diode characteristics

 

These are the characteristics of the Impatt diode, which shows the current pulse actually at the cathode terminal.

The RF voltage is there at a negative peak, and voltage and current in the Impatt diode are 180˚ out of phase.

An RF negative resistance exists at the Impatt diode junction, this particular resistance factor is used at the oscillator and amplifier.

Features of Impatt diode

  1. Operating frequency = 4GHz to 200GHz
  2. Operation principle = avalanche multiplication
  3. Output power = 1w CW and >400watt pulsed
  4. Efficiency = 3% CW and 60% pulsed below 1GHz, more powerful than GUNN diode
  5. Noise figure = 30db

Advantages of Impatt diode

  • The microwave diode has a high power capability compared to other diodes.
  • Output is reliable
  • Less expensive
  • Reliable operation at high temperatures
  • Compact size

Disadvantages of Impatt diode

  • High noise figure
  • They offer a low turning range
  • High operation current
  • High spurious AM/FM noise
  • They offer high sensitivity to different operating conditions

Impatt diode in microwave

The Impatt diode is a microwave diode, which can handle 3GHz to 100GHz frequency range, thus they can the ability to generate microwaves or work with microwaves.

 Impatt diode applications

  • Voltage-controlled oscillator circuit
  • Low power radar systems
  • Telecommunication receivers
  • Injection locked amplifiers
  • Cavity stability Impatt diode oscillators
  • Intrudes alarm
  • General detector using RF technology
  • Microwave oscillator
  • Parametric amplifier
  • Microwave generator
  • Telecommunication transmitters

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