Impatt vs. Trapatt vs. Baritt Diode: A Comparison

This article breaks down the key differences between Impatt, Trapatt, and Baritt diodes, which are all semiconductor devices capable of generating negative resistance at microwave frequencies. These diodes leverage carrier impact ionization and drift within a high-intensity electric field when reverse-biased.

In 1958, W.T. Read introduced the concept of the avalanche diode, which paved the way for these technologies.

Impatt Diode

Overview

• Full Name: Impact Ionization Avalanche Transit Time
• Developed By: R.L. Johnston (1965)
• Operating Frequency: 4 GHz to 200 GHz
• Principle of Operation: Avalanche multiplication
• Output Power: 1 Watt (CW), > 400 Watt (Pulsed)
• Efficiency: 3% (CW), 60% (Pulsed below 1 GHz)
• Noise Figure: 30dB (higher than Gunn diode)

Advantages:

• High power capability compared to other diodes.
• Reliable output.

Disadvantages:

• High noise figure.
• High operating current.
• High spurious AM/FM noise.

Applications:

• Voltage-controlled Impatt oscillators.
• Low-power radar systems.
• Injection-locked amplifiers.
• Cavity-stabilized Impatt diode oscillators.

Trapatt Diode

Overview

• Full Name: Trapped Plasma Avalanche Triggered Transit
• Developed By: H.J. Prager (1967)
• Operating Frequency: 1 to 3 GHz
• Principle of Operation: Plasma avalanche
• Output Power: 250 Watt at 3 GHz, 550 Watt at 1 GHz
• Efficiency: 35% at 3 GHz, 60% pulsed at 1 GHz
• Noise Figure: ~60dB (Very high)

Advantages:

• Higher efficiency than Impatt diodes.
• Very low power dissipation.

Disadvantages:

• Not suitable for CW (continuous wave) operation due to high power densities.
• High noise figure (~60dB).
• Upper frequency limit is below the millimeter band.

Applications:

• Microwave beacons.
• Instrument landing systems.
• Local oscillators (LO) in radar.

Baritt Diode

Overview

• Full Name: Barrier Injection Transit Time
• Developed By: D.J. Coleman (1971)
• Operating Frequency: 4 GHz to 8 GHz
• Principle of Operation: Thermionic emission
• Output Power: Few milliwatts
• Efficiency: 5% (low frequency), 20% (high frequency)
• Noise Figure: ~15dB (low)

Advantages:

• Less noisy than Impatt diodes.
• Low noise figure of 15dB at C-band when used in a Baritt amplifier.

Disadvantages:

• Narrow bandwidth.
• Limited power output (few milliwatts).

Applications:

• Mixers
• Oscillators
• Small-signal amplifiers

Key Differences

The major functional difference lies in the mechanism for carrier drift:

• Baritt Diodes: Rely on “Thermionic emission” for minority carrier drift.
• Impatt Diodes: Utilize the “Avalanche effect” for minority carrier drift.

This difference makes Baritt diodes significantly less noisy than Impatt diodes.

Summary Table