Module 2.2: Semiconductor Diode
Average AC Resistance
resistance associated with the device when a large signal is used as an input to produce a broad a swing; to determine a value-straight line is drawn between 2 intersections established by the maximum and minimum values of input values
Static Resistance or DC
resistance of the diode at the quiescent point; result in an operating diode on the characteristic curve that will not change in time the higher the current through a diode, the lower is the dc resistance level
simplified diode model
second approximation; the diode in forward biased-has some threshold voltage but with no resistance; reverse biased- it is an open circuit
bias
use o f a dc voltage to establish a certain operating conditions for an electronic device
Breakdown voltage
maximum voltage that can be handled by the junction diode; also known as peak reverse voltage or peak inverse voltage
Ideal diode model
1st approximation; if the turn on voltage is very small compared to other voltages in the circuit and diodes resistance is negligible compare to other; representing it as a switch
400V
PIV of Germanium
1000v
PIV of Si
Barrier Potential
The amount of energy required to produce full conduction across the pn junction in forward bias.
pn junction diode
a microelectronics device composed of adjacent layers of p-type and n-type semiconductors that serves to pass current in one direction while (essentially) blocking current in the opposite direction
Diode Equivalent Model
aka Diode equivalent circuit; combination of circuit element that best represents the actual characteristics of a semi conductor under a specific operating condition
transition region Capacitance
aka depletion region capacitance; capacitance in reverse bias condition
diffusion capacitance
aka storage capacitance; capacitance in forward bias region and always greater in value than depletion region capacitance
Dynamic Resistance or AC
application of an ac voltage will move the instantaneous operating point up and down a particular region since the value of ID and VD will also vary; resistance changes as you move the V-I curve; resistance of a forward bias diode is not constant over the entire curve
diode capacitance
electronic devices are inherently sensitive to a very high frequencies; 2 capacitive effects
PN Junction Diode
formed by doping one-half of intrinsic Si or Ge with a p-type dopants and the other half with an n-type dominant
PN Junction
formed when an n-type and a p-type materials are brought together; formed at the boundary between 2 regions
reverse current will drastically change
if the external reverse bias is increased to a value called breakdown voltage
high reverse bias voltage
imparts energy to free minority electrons; collide with atoms with enough energy to knock valence electrons out of orbit and into the conduction band
avalanche
multiplication of conduction electrons; results in a very high reverse current and can damage the PN Junction structure because of the excessive heat dissipation
biasing pn junction
no electrons move through the PN Junction at equilibrium and since the flow of electrons is electrical current, there is no electrical current through the PN junction
Depletion Region
region near the PN Junction is depleted of change carriers (both electrons and holes) due to diffusion across the junction
true
silicon diodes have higher PIV and current ratings than germanium
100 C
temperature range for Ge
200 C
temperature range for Si
conduction electrons
these newly conducted free electrons are also high in energy and repeat the process
piecewise linear diode model
third approximation; diode in forward bias has some threshold voltage and a bulk resistance; reverse biased- an open circuit
knee voltage
voltage wherein the sudden increase in current starts
forward bias
when the negative terminal of the AC source is connected to the N-end and the positive terminal to the P-end, electrons and holes flow toward each other, reducing the barrier voltage, allowing current to flow across the junction and the external circuit.
reverse bias
when the positive terminal of the AC source is connected to the N-end and the negative terminal to the P-end, electrons and holes move away from each other, increasing the barrier voltage and preventing current across the junction; making the depletion region wider expecting no current flow