Tunnel Diode and Back Diode

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:

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

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:

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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