Coisas especiais

Question 1

Diodo de Zener

Answer 1

-A Zener diode is a type of diode that
permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage

Question 2

Varactor

Answer 2

-A varactor diode is a P-N junction diode that changes its capacitance and the series resistance as the bias applied to the diode is varied

-The absolute capacitance of the varactor diode contributes to the total capacitance of the LC circuit in which it operates, and thus determines the frequency of operation

• The change of capacitance of a varactor diode with the change of applied reverse bias voltage is what governs the change of the frequency or the phase of the signal.
• The property of capacitance change is utilized to achieve a change in the frequency and/or the phase of an electrical circuit.

-The capacitance and the capacitance change characteristic are both functions of the doping structure

Question 3

Q factor

Answer 3

– The Q factor, also known as the figure of merit and the quality factor, is an important
parameter for a varactor diode since it determines the frequency limit applicability
for the diode.
– In the case of a high Q tuning diode, the better physical model is the series
equivalent circuit since the depleted region is an almost perfectly pure capacitance

Question 4

Tunneling diode

Answer 4

– Tunnel diode is the p-n junction device that exhibits negative resistance. That means when the voltage is increased the current through it decreases

• Heavily-doped p-n junction
  – Tunneling goes exponentially with tunneling distance (Requires junction to be abrupt)

Question 5

Tunneling diode STEPS

Answer 5

1: at zero bias there is no current flow
2: Electrons in the conduction band of the n region will tunnel to
the empty states of the valence band in p region. This will create a forward
bias tunnel current.
3: With a larger voltage the energy of the majority of electrons in the n-region is equal to that of the empty states (holes) in the valence band of p-region; this will produce maximum tunneling current
4: As the forward bias continues to increase, the number of electrons in the n side that are directly opposite to the empty states in the valence band (in terms of their energy) decrease. Therefore, a decrease in the
tunneling current will start
5: As more forward voltage is applied, the tunneling current drops to zero. But the regular diode forward current due to electron – hole injection increases due to lower potential barrier
6: With further voltage increase, the tunnel diode I-V characteristic is
similar to that of a regular p-n diode.
(VER DESENHO)
7: Under reverse bias, electrons in the valence band of the p side tunnel directly towards the empty states present in the conduction band of the n side creating large tunneling current which increases with the application of reverse voltage.