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