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Wednesday, September 12, 2007

Tunnel Diode and Back Diode

TUNNEL DIODE

A tunnel diode is a semiconductor with a negative resistance region that results in very fast switching speeds , up to 5 GHz. The operation depends upon a quantum mechanic principle known as "tunneling" wherein the intrinsic voltage barrier (0.3 Volt for Germanium junctions) is reduced due to doping levels which enhance tunneling. Refering to the curves below, superimposing the tunneling characteristic upon a conventional P-N junction, we have:

6A.jpg (13541 bytes)

Resulting in a composite characteristic which is the tunnel diode characteristic curve.

6B.jpg (18060 bytes)

The negative resistance region (between points A and B) is the important characteristic for the tunnel diode. In this region, as the voltage is increased, the current decreases; just the opposite of a conventional diode. The most 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 diode is a tunnel diode with a suppressed Ip and so approximates a conventional diode characteristic See the comparison below:

6C.jpg (11065 bytes)

The reverse breakdown for tunnel diodes is very low, typically 200mV, and the TD conducts very heavily at the reverse breakdown voltage. Referring to the BD 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 300 mV (for germanium) and a voltage swing of only 500mV is required for full range operation.

Typical tunnel diodes supplied by American Microsemiconductor

Part Number

Ip

Peak Point Current (mA)

IV

Valley Point Current Max. (mA)

C

Capacitance Max. (pF)

VP

Peak Point Voltage Typ. (mV)

VV

Valley Voltage Typ. (mV)

Vfp

Forward Peak Voltage Typ. (mV)

RS

Series Resist. Max. (ohms)

-G

Negative Conductance (mhosx10-3)

fRO

Resistive Cutoff Frequency 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 Number

IP

Peak point current (mA)

IV

Valley Point Current Max. (mA)

C

Capacitance Max. (pF)

VP

Peak Point Voltage Typical (mV)

VV

Valley Voltage Typical (mV)

Vfp

Forward Voltage Typical (mV)

RS

Series Resist. Typical (ohms)

T

Rise Time Typical (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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