PETER PAZMANY CATHOLIC UNIVERSITY...Types of diodes: Tunnel diode • The characteristics of the tunnel diode indicate the negative resistance region. Note that this is only a small

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Development of Complex Curricula for Molecular Bionics and Infobionics Programs within a consortial* framework**

Consortium leader

PETER PAZMANY CATHOLIC UNIVERSITYConsortium members

SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER

The Project has been realised with the support of the European Union and has been co-financed by the European Social Fund ***

**Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben

***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg.

PETER PAZMANY

CATHOLIC UNIVERSITY

SEMMELWEIS

UNIVERSITY

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Peter Pazmany Catholic University

Faculty of Information Technology

ELECTRICAL MEASUREMENTS

Semiconductors basics: diodes and transistors

www.itk.ppke.hu

(Elektronikai alapmérések)

Félvezető alapismeretek: a dióda és a tranzisztor

Dr. Oláh András

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Electrical measurements: Semiconductors basics: diodes and transistors

Lecture 6 review• Introduction to Circuit Theory• Defnitions of corresponding quantities• History of Circuit Theory• Definition of elements• The Kirchhoff laws• Classificition of elements• Linear resistive circuits• Thevenin and Norton equivalent circuits• System and Networks• Linear dynamic circuits

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Outline• Nonlinear resitive components• Diode: p-n junction• Actuel diode characterestics and used models• Nonlinear element in linear resistive network• Load-line analysis (graphical method)• Types and applications of diodes• Field Effect Transistor (FET)• JFET and MOSFET operating characteristics


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Nonlinear components


i=Φiu=Fi(u)u=Φui=Fu(i)

Question:How can it be implemented?

Answer:Semiconductive devices

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• The electrical characteristics ofsilicon and germanium are improvedby adding materials in a processcalled doping.

• There are just two types of dopedsemiconductor materials:– n-type materials contain an excess of

conduction band electrons. (eg:Phosphor)

– p-type materials contain an excess ofvalence band holes.(eg.: Boron)


Diode: Si crystal and doping

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Diode: p-n junction• One end of a silicon crystal can be doped as a p-type material

and the other end as an n-type material. The result is a p-njunction.


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Diode production: planar structure


200μm

p

SiO2

n

Metal bearing

Next slides

Materials commonly used in the development of semiconductor devices:

Silicon (Si)Germanium (Ge)Gallium Arsenide (GaAs)

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• The excess conduction-band electronson the n-type side are attracted to thevalence-band holes on the p-type side.

• The electrons in the n-type materialmigrate across the junction to the p-type material (electron flow).

• The electron migration results in anegative charge on the p-type side ofthe junction and a positive charge onthe n-type side of the junction.

• The result is the formation of adepletion region around the junction.


Diode: p-n junction (cont’)

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• External voltage is applied, a diodehas three operating conditions:– No bias: uD = 0V → iD = 0 A– Reverse bias: external voltage across the

p-n junction in the opposite polarity of thep- and n-type materials. uD<0V → iD=0A

– Forward bias: external voltage across thep-n junction in the same polarity as the p-and n-type materials. uD>0V → iD>0A


Diode: p-n junction (cont’)

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Actuel diode characterestics

T0 1

uU

ii u I e⎛ ⎞

= Φ = −⎜ ⎟⎜ ⎟⎝ ⎠

0T ln 1

iI

uu i U e⎛ ⎞

= Φ = +⎜ ⎟⎜ ⎟⎝ ⎠

BT 26mVk TU

q= ≈

I0 is the reverse bias saturation current, UT is the thermal voltage.

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• The Zener region is in the diode’sreverse-bias region. At some point thereverse bias voltage is so large thediode breaks down and the reversecurrent increases dramatically.

• The maximum reverse voltage thatwon’t take a diode into the zenerregion is called the peak inversevoltage or peak reverse voltage.

• The voltage that causes a diode toenter the zener region of operation iscalled the zener voltage (uZ).


Zener range (or breakdown range)

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Basic linear elements:– Resistor, R, [Ω] (Ohms)– Nonlinear resistor (eg. diodes)


Nonlinear resistive networks (circuits)

Thevenin equivalent

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Nonlinear resistive circuits (or networks)


KVL and KVC:

s 00

D R

R D

u u ui i− + + =

− =

Charateristics of elements:

The system function:Nonlinear equation

0 1 .D

T

R R

uU

D

u Ri

i i e

=

⎛ ⎞= −⎜ ⎟⎜ ⎟

⎝ ⎠

0 1 0D

T

uU

s Du Ri e u⎛ ⎞

− + − + =⎜ ⎟⎜ ⎟⎝ ⎠Question: How can it be solved?

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• The load line plots all possible combinations of diode current (iD) and voltage(uD) for a given circuit. The maximum iD equals us/R, and the maximum uDequals us.

• The point where the load line and the characteristic curve intersect is the Q-point (equlibrium, or operation point set by the linear networks), whichidentifies iD and uD for a particular diode in a given circuit.


Load-line analysis (graphical method)

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Newton-Raphson iterative method

( )( )1

nn n

n

f xx x

f x+ = −′

( ) ( )( )( )( )( )

D1D D

D

nn n

n

f uu u

f u+ = −

′

( )D

TD s 0 D1

uUf u u R I e u

⎛ ⎞= − + ⋅ − +⎜ ⎟⎜ ⎟

⎝ ⎠

( ) 0f x =

( )D

T0D

T

1uUR If u e

U⋅′ = +

xnxn+1x

f(x)

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Some useful models of diode characteristics1. Piecewise linear model:

2. Series loss resistor model:

0T lossln 1

iI

uu i U e R i⎛ ⎞

= Φ = + + ⋅⎜ ⎟⎜ ⎟⎝ ⎠

( )D 0

DD 0 D 0

0 u ui

G u u u u≤⎧

= ⎨ − ≥⎩

G = ∞

u0 = 0

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• Semiconductors react differently toDC and AC currents.

• There are two types of resistance:– DC (static) resistance– AC (dynamic) resistance

For a specific applied DC voltageuD, the diode has a specific currentiD, and a specific resistance RD.


Resistance levels: static resistance

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• Semiconductors react differently toDC and AC currents.

• There are two types of resistance:– DC (static) resistance– AC (dynamic) resistance:

In the forward bias region:

In the reverse bias region:


Resistance levels: dynamic resistance

DD

D ,Q Qu i

durdi

=

D lossD

26mVr Ri

= +

Dr = ∞

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• Zener diode• Light-emitting diode• Diode arrays• Schottky diode• Varactor diode• Power diodes• Tunnel diode• Photodiode• Photoconductive cells• IR emitters• Liquid crystal displays• Solar cells• Thermistors


Types of diodes: Zener diode

A Zener is a diode operated in reverse bias at theZener voltage (uZ). Common Zener voltages arebetween 1.8 V and 200 V.

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Types of diodes: LED

An LED emits photons when it is forwardbiased.These can be in the infrared or visiblespectrum. The forward bias voltage is usually inthe range of 2 V to 3 V.Applications:

–Instrumentation circuits as a sensor–Alarm system sensor–Detection of objects on a conveyor belt

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Types of diodes: Schottky diode

Characteristics:– Lower forward voltage drop (0.2-.63V)– Higher forward current (up to 75A)– Significantly lower voltage drop– Higher reverse current– Faster switching rate

• Applications– High frequency switching applications– Low-voltage high-current applications– AC-to-DC converters– Communication equipment– Instrumentation circuits

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Types of diodes: Tunnel diode

• The characteristics of the tunnel diodeindicate the negative resistance region.Note that this is only a small region ofthe characteristic curve. If the forwardbias voltage is in the negative resistanceregion then the diode can be used as anoscillator.

• Applications:– Oscillators– Switching networks– Pulse generators

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The diode only conducts when it is forward biased, therefore only half of the ACcycle passes through the diode to the output.The DC output voltage is 0.318Up, where Up is the peak AC voltage.


Application of regular diodes: rectification

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Four diodes are connected in a bridge configuration.UDC = 0.636Up


Application of simple diodes: rectification (cont’)

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• There are two types oftransistors:– pnp– npn

• The terminals arelabeled:– E - Emitter– B - Base– C - Collector


Bipolar transistor construction

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Bipolar transistor operation• With the external sources, VEE (or UEE) and VCC (or UCC),

connected as shown:– The emitter-base junction is forward biased– The base-collector junction is reverse biased


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Bipolar transistor configuration: common-base• The base is common to both input (emitter–base) and output (collector–

base) of the transistor.


Operation mode B-E junction B-C junction

Cutoff Close (VBE<0) Close(VCB>0)

Normal active Open(VBE>0) Close

Inverse active Close Open(VCB<0)

Saturation Open Open

IE = IC+IB (Kirchhoff current law)

IC = AIE (transitor equation)

C

B 1I A BI A

= =−

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Bipolar transistor configuration: common-collector• The input is on the base and the output is on the emitter.


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Bipolar transistor configuration: common-emitter• The emitter is common to both input (base-emitter) and

output (collector-emitter).• The input is on the base and the output is on the collector.


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Common-emitter characteristics


Collector CharacteristicsBase Characteristics

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Bipolar transistor Modeling• A model is an equivalent circuit that represents the AC

characteristics of the transistor.• A model uses circuit elements that approximate the behavior of

the transistor.• There are two models commonly used in small signal AC

analysis of a transistor:– re model: the bipolar transistor is basically current-controlled device;

therefore the re model uses a diode and a current source to duplicate thebehavior of the transistor.

– Hybrid equivalent model (→simplified equivalent model)


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Simplified equivalent model: Ideal transistor = current controlled current sources


BEB

D

Uir

=C Bi iβ= ⋅

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Field Effect Transistor (FET)• Similarities:

– Amplifiers– Switching devices– Impedance matching circuits

• Differences:– FETs are voltage controlled devices. Bipolar transistors are current

controlled devices.– FETs have a higher input impedance. Bipolar transistors have higher

gains.– FETs are less sensitive to temperature variations and are more easily

integrated on ICs.– FETs are generally more static sensitive than Bipolar transistors.


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• JFET: Junction FET• MOSFET: Metal–Oxide–

Semiconductor FET– D-MOSFET: Depletion MOSFET– E-MOSFET: Enhancement

MOSFET


FET types

There are three terminals:– Drain (D) and Source (S) are

connected to the n-channel– Gate (G) is connected to the p-

type material

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JFET operating charactericticsThere are three basic operating conditions for a JFET:

VGS = 0, VDSincreasing to some

positive value

Pinch OffVGS < 0, VDS at

some positive value

Voltage-controlled resistor:At the pinch-off point any further increase in UGS does not produce any increase in ID. VGS at pinch-off is denoted as Vpoff.

ID is at saturation or maximum. It is referred to as IDSS.

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JFET transfer characteristics

In a JFET, the relationship of VGS (input) and ID(output) is a little more complicated:

GS

P

2

1D DSSVV

I I⎛ ⎞⎜ ⎟−⎜ ⎟⎝ ⎠

=

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• JFET: Junction FET• MOSFET: Metal–Oxide–

Semiconductor FET– D-MOSFET: Depletion MOSFET– E-MOSFET: Enhancement

MOSFET


FET types

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MOSFET operating charactericticsA depletion-type MOSFET can operate in two modes:•Depletion mode:

–When VGS = 0 V, ID = IDSS

–When VGS < 0 V, ID < IDSS

–The formula used to plot the transfer curve still applies:

•Enhancement mode:

2

GSD DSS

Poff

1 VI IV

⎛ ⎞= −⎜ ⎟

⎝ ⎠

These devices are off at zero gate–source voltage UGS, and can be turned on bypulling the gate voltage in the direction of the drain voltage.

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Summary• Diodes are two-terminal devices that conduct current easily in one

direction, but not in the other.• The ideal diode model is a short circuit for forward currents and an open

circuit for reverse voltages.• Zener diodes are intended to operate in the breakdown region.• Transistors are three-terminal devices.• Circuits containing a nonlinear device can be analyzed using a graphical

technique called a load-line analysis.• The analysis of nonlinear electronic circuits is often accomplished in two

steps: First, the dc operating point is determined, and a linear small-signalequivalent circuit is found; second, the equivalent circuit is analyzed.

Next lecture: Nonlinear resistive networks

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PETER PAZMANY CATHOLIC UNIVERSITY...Types of diodes: Tunnel diode • The characteristics of the tunnel diode indicate the negative resistance region. Note that this is only a small