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Reference Guide

Permachart - Marketing Reference Guide: Semiconductor Device, Precision Rectifier, Envelope Detector

2 pages1010 viewsFall 2015

Department
Electrical Engineering
Course Code
4400:307
Professor
All
Chapter
Permachart

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Electronics I
Laplace transform applies only to time functions that are zero
for t< 0; it implicates complex frequency s= jv+ s
Waveforms
Semiconductor Devices
A Fourier series applies to signal waveforms that are periodic
functions of time
• A periodic signal with a complex waveform has a discrete
spectrum of harmonic (sine/cosine) waveforms of magnitudes
determined by Fourier series
A Fourier transform applies to signal waveforms that are
non-periodic functions of time
• A non-periodic waveform has a continuous spectrum of
harmonic components determined by Fourier transform
Diodes are 2-terminal devices that pass current in 1 direction
When a large enough reverse voltage is applied to any diode,
it will conduct current in the reverse direction (breakdown)
Germanium Diodes
Advantage: Forward voltage drop for silicon diodes is about
0.7 V, compared to 0.3 V for germanium diodes
Disadvantage: Breakdown voltages for germanium diodes are
usually less than 100 V, compared to 50–1000 V for silicon
Ideal diode: Diode is either an open circuit or a short circuit
• Diode designed to operate in the breakdown region;
used to establish a fixed DC voltage or limit a
varying signal to a peak voltage
• Constructed to work in the reverse-bias direction
Zener diode is not in breakdown if reverse-bias current is
insufficient; instead, it will act as an open circuit
• A diode that will emit visible or infrared light
when sufficient forward voltage is applied
• When injected, minority carriers in forward-biased
pn junction recombine to release energy
With Si and Ge, energy is released as heat
• With GaAs, energy is released as photon at red, yellow or
green wavelengths (depending on impurities added)
Diodes
• Any two-terminal linear circuit can be replaced by a single
voltage source in series with single resistance (Thevenin
circuit) or current source in parallel with resistor (Norton circuit)
Semiconductor Junctions
N-type: Semiconductor doped with donors (phosphorus, arsenic,
antimony) which have loosely bound electrons
P-type: Semiconductor doped with acceptors (boron, gallium,
indium) which have atoms that leave an electron vacancy (hole)
Hole: The mobile positive charge in semiconductor materials
Doping: The process of adding a controlled amount of a specific
impurity to control a material’s conductivity
Forward bias: Voltage required to turn on a pn junction
Reverse bias: Voltage applied to a pn junction that prevents the
junction from conducting
• In the presence of an electric field,
a hole takes an electron from an
atom of silicon (usual
semiconductor material)
• This event is repeated in a
consistent direction,
resulting in conduction by hole
P-N JUNCTIONS
• An npn transistor consisting of two junctions; a p-type material
is placed between two n-type materials
• Almost all of the electrons injected from the emitter into the
thin base region are collected by the collector
• A doped semiconductor provides a channel for flow of current
from drain D to source S; p-type at the center controls current
• Positive voltage applied to Dcauses IDto flow downwards
(i.e., electrons upwards)
• When negative voltage is applied to G, junction is reverse-biased;
depletion region eliminates conduction electrons from channel
• FET has very small gate current and low voltage gain
BIPOLAR SEMICONDUCTOR
FIELD-EFFECT TRANSISTOR (FET)
iI v
V
gdi
dv
I
V
v
V
gIIV
DDSS GS
P
mD
GS
DSS
P
GS
P
mDDSSP
=−
≡=
=−
()
1
21
2
2
• Biasing the FET means
to select a point on
the curve around
which it will
operate
ZENER DIODE
• Metal semiconductor junction diode
• Has low 0.3 V forward voltage drop
Al or Pt may act as acceptor when in contact with n-type Si
SCHOTTKY DIODE
LIGHT-EMITTING DIODE (LED)
• A diode that produces a current or a voltage in
response to light
• Reverse saturation current depends on generation
of hole-electron pairs by average thermal energy of the crystal
• Current can be increased further by light illumination
PHOTODIODE (LIGHT-SENSITIVE DIODE)
• A diode that acts as a capacitance controlled
by the reverse-bias voltage
• No forward bias due to high shunt conductance
VARACTOR (VARICAP DIODE)
A peak detector is a circuit that hold the peak value of the input
• The capacitor in a peak detector most hold its charge for the duration of
the signal measurement
• If RCproduct is very large, v3equals the highest peaks in v2
• If RCproduct is small enough, v3will be able to follow the envelope of v2
• Peak detector is used in radio receiver as automatic gain control
• Convert to DC power supply by
putting capacitor parallel with RL
Diode bridge: Four diodes connected
as a bridge
circuit to
provide for
full-wave
rectification
FULL-WAVE BRIDGE RECTIFIER
LAPLACE TRANSFORM
• Envelope detector used in AM radio circuits to
recover low frequency audio envelope modulated on
a high frequency carrier
• Rate of change of v
emust satisfy
dv dt
vRC
e
e
1
Clipper: A circuit that
regulates voltage by
eliminating any part of a
signal that is greater in
magnitude than set voltage
Rectification:
Elimination of
positive or
negative portion
of signal
Half-wave rectifier: Uses only one-half of input cycle; negative half of sine wave is lost
Full-wave rectifier: Uses all of input cycle; efficiency increases as all incoming ac is used
Diodes in Circuits
PEAK DETECTOR ENVELOPE DETECTOR
Equivalent Circuits
FOURIER SERIES & FOURIER TRANSFORM
Diode or
metallic rectifier Zener diode Bipolar voltage limiter
(symmetrical zener diode)
AK
Tunnel diode
Pin diode Photodiode
(photosensitive type)
Light emitting
diode (LED)
Temperature
sensitive diode
Trigger diac
(npn)
KA
Trigger diac
(pnp)
AK
Bidirectional
trigger diac (npn)
TT
Bidirectional
trigger diac (pnp)
TT
Phototransistor (npn)
EC
or EC
B
n-type gate
Transistor
(pnp)
EC
B
Transistor
(npn)
EC
B
G
AK
p-type gate
G
AK
Semiconductor controlled rectifiers (SCRs)
Thyristor
bidirectional triode
G
TT
pnp transverse-biased base transistor
or
Darlington-type transistor
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