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Tunnel Diode and Back Diode Tutorial

A tunnel diode is a semiconductor diode with a negative resistance region that allows very fast switching speeds, up to 5 GHz. The operation of the tunnel diode depends upon a quantum mechanic principle known as “tunneling” wherein the intrinsic voltage barrier (0.3 Volt for Germanium tunnel diodes and 0.7 Volt for Silicon tunnel diodes junctions) is surmounted due to high doping levels which enhance tunneling. Referring to the curves below: superimposing the tunneling characteristic of the tunnel diode upon a conventional germanium P-N junction, we have:

6A.jpg (13541 bytes)

Resulting in a composite characteristic which is the tunnel diode characteristic curve shown below

6B.jpg (18060 bytes)

The negative resistance region of the tunnel diode (between points A and B) is an important characteristic for the tunnel diode. In this region, as the voltage is increased, the current decreases (the negative resistance region); just the opposite of a standard diode where the forward resistance characteristic is always positive. Other important specifications for the tunnel diode are the Peak Voltage (Vp), Peak Current (Ip), Valley Voltage (Vv), and Valley Current (Iv).

BACK DIODE

A back or backward diode is a tunnel diode with a suppressed Ip and so more closely approximates a conventional diode characteristic. See the comparison below:

6C.jpg (11065 bytes)

The reverse breakdown for the tunnel diodes is very low, typically 200mV, and the tunnel diode conducts very heavily at the reverse breakdown voltage. Now referring to the Back Diode curve, the back diode conducts to a lesser degree in a forward direction. It is the operation between these two points that makes the back diode important. Forward conduction begins at 300mV (for germanium) and a voltage swing of only 500mV is needed for full range operation. In a Back Diode, the negative characteristic is used as the forward direction and the positive characteristic is used as the negative diode direction.

Typical tunnel diodes supplied by American Microsemiconductor

Part Number Ip
Peak Point Curr
(mA)
IV
Valley Point Curr Max.
(mA)
C
Cap.
Max.
(pF)
VP

Peak Point Volt Typ.
(mV)
VV
Valley Volt Typ.
(mV)
Vfp
Forward Peak Volt Typ.
(mV)
RS
Series Resist. Max.
(ohms)
-G
Negative Conduct.
(mhosx10-3)
fRO
Resist. Cutoff Freq. Typ.
(GHz)
1N3712 1.0 + 10% 0.18 10 65 350 500 4.0 8 Typ. 2.3
1N3713 1.0 + 2.5% 0.14 5 65 350 510 4.0 8.5 + 1 3.2
1N3714 2.2 + 10% 0.48 25 65 350 500 3.0 18 Typ 2.2
1N3715 2.2 + 2.5% 0.31 10 65 350 510 3.0 19 + 3 3.0
1N3716 4.7 + 10% 1.04 50 65 350 500 2.0 40 Typ. 1.8
1N3717 4.7 + 2.5% 0.60 25 65 350 510 2.0 41 + 5 3.4
1N3718 10.0 + 10% 2.20 90 65 350 500 1.5 80 Typ. 1.6
1N3719 10.0 + 2.5% 1.40 50 65 350 510 1.5 85 + 10 2.8
1N3720 22.0 + 10% 4.80 150 65 350 500 1.0 180 Typ. 1.6
1N3721 22.0 + 2.5% 3.10 100 65 350 510 1.0 190 + 30 2.6

TYPICAL ULTRA HIGH-SPEED SWITCHING TUNNEL DIODES

SUPPLIED BY AMERICAN MICROSEMICONDUCTOR

Part Num.

IP

Peak point curr.
(mA)

IV


Max.
(mA)

C

Cap.
Max.
(pF)

VP

Peak Point Volt.
Typ.
(mV)

VV


Typ.
(mV)

Vfp

For.
Volt.
Typ
(mV)

RS

Typ
ohms

T

Rise Time Typ
psec

TD-261

2.2 + 10%

0.31

3.0

70

390

500-700

5.0

430

TD-261A

2.2 + 10%

0.31

1.0

80

390

500-700

7.0

160

TD-262

4.7 + 10%

0.60

6.0

80

390

500-700

3.5

320

TD-262A

4.7 + 10%

0.60

1.0

90

400

500-700

1.7

350

TD-263

10.0 + 10%

1.40

9.0

75

400

500-700

1.7

350

TD-263A

10.0 + 10%

1.40

5.0

80

410

520-700

2.0

190

TD-263B

10.0 + 10%

1.40

2.0

90

420

550-700

2.5

68

TD-264

22.0 + 10%

3.80

18.0

90

425

600 Typ.

1.8

185

TD-264A

22.0 + 10%

3.80

4.0

100

425

550-700

2.0

64

TD-265

50.0 + 10%

8.50

25.0

110

425

625 Typ.

1.4

100

TD-265A

50.0 + 10%

8.50

5.0

130

425

640 Typ.

1.5

35

TD-266

100 + 10%

17.50

35.0

150

450

650 Typ.

1.1

57

TD-266A 100 + 10% 17.50

6.0

180

450

650 Typ.

1.2

22

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