IMPATT,TRAPATT& BARITT DIODE

1. AVALANCHE TRANSIT TIME
DEVICES
KUNAL KANT SINGH
RAJYA KHATOON
ECE (7th sem.)
CIST, BHOPAL 1

2.  It is possible to make a microwave diode exhibit
negative resistance by having a delay between
voltage and current in an avalanche together with
transit time through the material.
Such devices are called
avalanche transit time devices.
 There are three distinct modes of Avalanche
Devices:-
1) IMPATT (Impact Ionization Avalanche Transit Time
Device)
2) TRAPATT (Trapped Plasma Avalanche Triggered
Transit Device)
3) BARITT (Barrier Injected Transit Time Device)
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3. 3
 It is a form of high power diode used in high
frequency electronics and microwave devices.
 Typically made from silicon carbides due to their
high breakdown fields.
 Frequency- 3 to 100 GHz
 High power capability
 Generate high level of phase noise – avalanche
process.
IMPATT DIODE :-

4. 4
WORKING:-
 An extremely high voltage is applied.
 A normal diode will breakdown, but IMPATT is
constructed such that it withstand these conditions
easily.
 Such a high potential causes flow of minority
charge carriers across junction.

5.  Increased velocity of electrons and holes results
additional electrons & holes by knocking out of
crystal structure, called Impact ionization.
 These additional C.C. Continue at junction &
snowball into avalanche, but since it’s a
multiplication process avalanche is not instant.
 This process takes time and results in 90˚ phase
shift b/w voltage and current.
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6. PERFORMANCE CHARACTERISTICS:-
 Efficiency- 30% (theoretical) ,<30% (practical)
 Frequency- 1 to 300 GHz
 Maximum output power for single diode – 4W
 Several diodes combined- 40W
 Pulse powers - 4W
ADVANTAGES:-
 High power capability
 High levels of performance
 Highly stable frequency
DISADVANTAGES:-
 Very noisy (avalanche is noisy process)
 Poor tuning range than Gunn diodes
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7. APPLICATIONS:-
 Microwave oscillators (e.g. MW Generators)
 Negative resistance amplification
 Intrusion alarm network, police radar
 FM( frequency modulation)
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TRAPATT DIODE
 It is derived from the IMPATT diode and is closely related to
it.
 It is a p-n junction diode characterized by the formation of a
trapped space charge plasma within the junction region.
 It was first reported by Prager in 1967.
 It is a high efficiency microwave generator capable of
operating from hundred MHz to several GHz.
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8.  The TRAPATT diode is typically represented by a current pulse
generator and the diode’s depletion-layer capacitance.
WORKING:-
 Depletion region filled with dense plasma of electrons and holes
that become trapped in low field region behind the zone. 8

9. 9
 At A, charge carriers due to thermal generation results in
charging of diode.
 When sufficient number of carrier is generated, the particle
current exceeds the external current and the electric field is
depressed throughout the depletion region, causing the voltage
to decrease. This portion of the cycle is known by “plasma
formation”.
 During this time interval ,a dense plasma of electrons and
holes is created. The voltage decrease to D.

10.  A large time is required to remove the plasma because total
plasma charge is large ,At point E plasma is removed.
 As the residual charge is removed, the voltage increases
from point E to point F . At point F all the charge generated
internally has been removed.
 At point G the diode current goes 0 for half period and the
voltage remains constant.
PERFORMANCE CHARACTERISTICS:-
 Efficiency- 15 to 40%
 Frequency- 3 to 50 GHz
 CW power -1-3 W
 Pulse powers = 1.2KW
 Noise figure - >30 dB
 Operating voltage- 60-150V
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11. ADVANTAGES:-
 High power capability
 High levels of performance
 Highly stable frequency
DISADVANTAGES:-
 Very noisy (avalanche is noisy process)
 Poor tuning range than Gunn diodes
APPLICATIONS:-
 In low power doppler radar
 Local oscillator for radar
 Radio altimeter
 Phased array radar
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12. BARITT
 It is the latest addition to the family of active
microwave diodes.
 It has long drift region similar to IMPATT.
 BARITT devices are improved version of IMPATT
devices.
 BARITT diode uses thermionic emission rather than
avalanche multiplication.
 The BARITT diode uses Injection and Transit-time
properties of minority carriers to produce a negative
resistance at microwave frequencies.
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13. 13
 BARITT consists of an emitter, base intermediate
drift or depletion region and collector.
 An essential requirement of BARITT is the
intermediate drift region by entirely depleted to
cause punch through to emitter base junction.

14.  A rapid increase in current with applied voltage is
due to the thermionic hole injection into
semiconductor.
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15. PERFORMANCE CHARACTERISTICS:-
 Efficiency- 1.8%
 Frequency- 4 to 10 GHz
 Power – 50mW
 Noise figure - 9dB
ADVANTAGES:-
 Less noisy than impatt diodes
 NF of 15dB at C band using Baritt amplifier
DISADVANTAGES:-
 Narrow bandwidth
 Limited few mW of power output
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16. APPLICATIONS
 Mixer
 Oscillator
 Small signal amplifier
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