CS301ES: ANALOG AND DIGITAL ELECTRONICS

UNIT - I
Diodes and Applications: Junction diode characteristics: Open circuited p-n junction, p-n junction as a rectifier, V-I characteristics, effect of temperature, diode resistance, diffusion capacitance, diode switching times, breakdown diodes, Tunnel diodes, photo diode, LED.
Diode Applications - clipping circuits, comparators, Half wave rectifier, Full wave rectifier, rectifier with capacitor filter.

1. DEPARTMENT OF
ELECTRONICS AND COMMUNICATION
ENGINEERING
Instructor
Mr. D V S RAMANJANEYULU
Assistant Professor
Accredited by NBA & NAAC with “A” Grade
CS301ES : ANALOG & DIGITAL ELECTRONICS

2. P.KIRAN KUMAR,ECE DEPARTMENT 2
UNIT -I : Diodes and Applications
UNIT –II : BJTs
UNIT –III : FETs and Digital Circuits
UNIT –IV : Combinational Logic Circuits
UNIT –V : Sequential Logic Circuits

3. P.KIRAN KUMAR,ECE DEPARTMENT 3
•IntegratedElectronics:AnalogandDigital
CircuitsandSystems,2/e,JaccobMillman,
ChristosHalkiasandChethanD.Parikh,Tata
McGraw-HillEducation,India,2010.
•DigitalDesign,5/e,MorrisManoandMichael
D.Cilette,Pearson,2011
TEXTBOOKS:

4. P.KIRAN KUMAR,ECE DEPARTMENT 4
UNIT -I : DIODES AND APPLICATIONS
DiodesandApplications:
Junctiondiodecharacteristics:Opencircuitedp-n
junction,p-njunctionasarectifier,V-Icharacteristics,
effectoftemperature,dioderesistance,diffusion
capacitance,diodeswitchingtimes,breakdowndiodes,
Tunneldiodes,photodiode,LED.
DiodeApplications:
Clippingcircuits,
Comparators,
Halfwaverectifier,
Fullwaverectifier,Rectifierwithcapacitorfilter.

5. P.KIRAN KUMAR,ECE DEPARTMENT 5
ADiodeisthesimplesttwo-terminalelectronic
device.Itallowscurrenttoflowonlyinonedirectionand
blocksthecurrentthatflowsintheoppositedirection.
Thetwoterminalsofthediodearecalledasanode
(+)andcathode(-).
DIODE
A
K
Symbol of a Diode

6. P.KIRAN KUMAR,ECE DEPARTMENT 6
The name diode is derived from “Di–Ode”
which means a device that has two electrodes.
Di –means Two (2)
Ode –means Electrodes
Diode: “Di –Ode”

7. P.KIRAN KUMAR,ECE DEPARTMENT 7
Formation of a Diode
IfaP-typeandanN-typematerialarebroughtclosetoeach
other,bothofthemjointoformajunction.
Asshowninthefigurebelow.

8. P.KIRAN KUMAR,ECE DEPARTMENT 8
P-typematerialhasholesasthemajoritycarriersand
anN-typematerialhaselectronsasthemajoritycarriers.
Asoppositechargesattract,fewholesinP-typetendtogo
toN-side,whereasfewelectronsinN-typetendtogotoP-
side.
Asbothofthemtraveltowardsthejunction,holesand
electronsrecombinewitheachothertoneutralizeandforms
ions.
Now,inthisjunction,thereexistsaregionwherethe
positiveandnegativeionsareformed,calledasPNjunction
orjunctionbarrier

9. P.KIRAN KUMAR,ECE DEPARTMENT 99
Diode’s Three Operation Regions
•In order to understand the operation of a diode,
it is necessary to study its three operation
regions: equilibrium, reverse bias, and forward
bias.

10. P.KIRAN KUMAR,ECE DEPARTMENT 10
TheformationofnegativeionsonP-sideand
positiveionsonN-sideresultsintheformationofa
narrowchargedregiononeithersideofthePN
junction.Thisregionisnowfreefrommovable
chargecarriers.

11. P.KIRAN KUMAR,ECE DEPARTMENT 11
Theionspresentherehavebeenstationaryand
maintainaregionofspacebetweenthem
withoutanychargecarriers.Asthisregionacts
asabarrierbetweenPandNtypematerials,this
isalsocalledasBarrierjunction.Thishas
anothernamecalledasDepletion
regionmeaningitdepletesboththeregions.

12. P.KIRAN KUMAR,ECE DEPARTMENT 12
Types of Diode

13. P.KIRAN KUMAR,ECE DEPARTMENT 13
ThePNjunctiondiodeisatwoterminaldevice,whichis
formedwhenonesideofthePNjunctiondiodeismade
withp-typeanddopedwiththeN-typematerial.
Forward & Reverse Biased

14. P.KIRAN KUMAR,ECE DEPARTMENT 14
Current-Voltage Relationship
Forward Bias:current exponentially
increases.
Reverse Bias:low leakage current equal
to ~I
o
Ability of pn junction to pass current in
only one direction is known as
“rectifying”behavior.
PN Junction: I-V Characteristics

15. P.KIRAN KUMAR,ECE DEPARTMENT 15
Effects of Temperature on V-I Characteristics
In the forward bias , it's shifts to 2.5mV per °C
In the reverse biased condition because the reverse
saturation current of a silicon diode doubles for every
10°C rose in temperature

16. P.KIRAN KUMAR,ECE DEPARTMENT 16
Diode resistance
Static Resistance or (DC resistance)
Forward Resistance R
f
Reverse Resistance R
r
Dynamic Resistance or (AC resistance)
Forward Resistance r
f
Reverse Resistance r
r

17. P.KIRAN KUMAR,ECE DEPARTMENT 17
Diode resistance
•ΔV/ΔI is called ac (dynamic) resistance of the diode because we
consider small change in voltage
•We would not want to calculate ac resistance between V=0.55V and
V=0.65V
•rd=ΔV/ΔI ohms
•The dc resistance of a diode is found by dividing the dc voltage
across it by dc current through it. DC resistance also called the static
resistance.
Rd=V/I ohms
•Diode is nonlinear in both the dc & the ac sense, that is, both its dc
& ac resistance change over a wide range.

18. P.KIRAN KUMAR,ECE DEPARTMENT 18
AC & DC Resistance
V (V)
I (mA)
00.1 0.60.50.40.30.2
0
40
10
20
30
ΔI
ΔV
r
D= ΔV / ΔI
R
D= V / I
AC ResistanceDC Resistance
r
D= V
T/ I

19. P.KIRAN KUMAR,ECE DEPARTMENT 19
Diode capacitance
•Transition capacitance (C
T)
The change of capacitance at the depletion
region can be defined as the change in
electric charge per change in voltage.
CT= dQ / dV
C=εA / W
Where,
CT= Transition capacitance
dQ = Change in electric charge
dV = Change in voltage
The transition capacitance can be
mathematically written as,

20. P.KIRAN KUMAR,ECE DEPARTMENT 20
•Diffusion capacitance or Storage capacitance (C
D)
,
•CD is due to the storage of minority
carriers in a forward biased diode
•It will dominate in the device only during
high frequency operation
•CD>CT

21. P.KIRAN KUMAR,ECE DEPARTMENT 21
switching characteristics of pn junction diode
The sudden change from forward to reverse and from reverse to forward bias, affects
the circuit. The time taken to respond to such sudden changes is the important criterion
to define the effectiveness of an electrical switch.
•The time taken before the diode recovers its steady state is called asRecovery
Time.(trr)
•The time interval taken by the diode to switch from reverse biased state to forward
biased state is called asForward Recovery Time.
•The time interval taken by the diode to switch from forward biased state to reverse
biased state is called asReverse Recovery Time.
Storage time− The time period for which the diode remains in the conduction
state even in the reverse biased state, is called asStorage time.
Transition time− The time elapsed in returning back to the state of non-
conduction, i.e. steady state reverse bias, is calledTransition time.

22. P.KIRAN KUMAR,ECE DEPARTMENT 22
Reverse recovery time (trr)= Storage time(Ts)+Transition time (Tt)

23. P.KIRAN KUMAR,ECE DEPARTMENT 23
Ideal vs practical diode

24. P.KIRAN KUMAR,ECE DEPARTMENT 24
Block diagram of a Power Supply

25. P.KIRAN KUMAR,ECE DEPARTMENT 25
Rectifiers
•Rectifier is a device which convert AC
voltage in to pulsating DC
•A rectifier utilizes unidirectional
conducting device Ex : P-N junction
diodes

26. P.KIRAN KUMAR,ECE DEPARTMENT 26
Types
•Depending up on the period of conduction
Half wave rectifier
Full wave rectifier
•Depending up on the connection procedure
Bridge rectifier

27. P.KIRAN KUMAR,ECE DEPARTMENT 27
HalfwaveRectifier
•Theprocessofremovingone-halftheinputsignalto
establishadcleveliscalledhalf-waverectification.
•InHalfwaverectification,therectifierconductscurrent
duringpositivehalfcycleofinputacsignalonly.
•Negativehalfcycleissuppressed.

28. P.KIRAN KUMAR,ECE DEPARTMENT 28
FullWaveRectifier
CircuithastwodiodesD1,D2andacentretap
transformer.
DuringpositivehalfcycleDiodeD1 conductsandduring
negativehalfcycleDiodeD2 conducts.
ItcanbeseenthatcurrentthroughloadRLisinthe same
directionforbothcycle.

29. P.KIRAN KUMAR,ECE DEPARTMENT 29
FullWaveBridgeRectifier
NeedforcentretappedPTiseliminated.
Consistsof4diodesinsteadof2.

30. P.KIRAN KUMAR,ECE DEPARTMENT 30
FullWaveBridgeRectifier
Duringperiodt=0tot=T/2D2and
D3areconductingwhileD1andD4
areinthe“off”state.

31. P.KIRAN KUMAR,ECE DEPARTMENT 31
Duringperiodt=T/2tot=TD1andD4are
conducting while D2 and D3 are in the “off”
state.

32. P.KIRAN KUMAR,ECE DEPARTMENT 32
Filters
A capacitor is added in parallel with the
load resistor of a half-wave rectifier to
form a simple filter circuit. At first there
is no charge across the capacitor
During the 1
st
quarter positive
cycle, diode is forward biased, and C
charges up.
V
C= V
O= V
S-V.
As V
S falls back towards zero, and
into the negative cycle, the
capacitor discharges through the
resistor R. The diode is reversed
biased ( turned off)
If the RCtime constant is large, the
voltage across the capacitor
discharges exponentially.

33. P.KIRAN KUMAR,ECE DEPARTMENT 33
Filters
During the next positive cycleof the input
voltage, there is a point at which the input
voltage is greater than the capacitor
voltage, diode turns back on.
The diode remains on until the input
reaches its peak value and the
capacitor voltage is completely
recharged.

34. P.KIRAN KUMAR,ECE DEPARTMENT 34
Quarter cycle;
capacitor
charges up
Capacitor discharges
through R since diode
becomes off
Input voltage is greater
than the capacitor
voltage; recharge before
discharging again
V
C= V
me
–t / RC
Since the capacitor filters out a large portion of the sinusoidal signal, it is called a
filter capacitor.
NOTE:V
mis the peak valueof the capacitor voltage = V
P-V
V
p
V
m

35. P.KIRAN KUMAR,ECE DEPARTMENT 35
Figure: Half-wave rectifier with smoothing capacitor.
Ripple Voltage, and Diode Current
V
r= ripple voltage
V
r= V
M–V
Me
-T’/RC
where T’ = time of the
capacitor to discharge to its
lowest value
V
r= V
M( 1 –e
-T’/RC
)
Expand the exponential in
series,
V
r = ( V
MT’) / RC
T’
Tp

36. P.KIRAN KUMAR,ECE DEPARTMENT 36
•If the ripple is very small, we can approximate T’ = T
p
which is the period of the input signal
•Hence for half wave rectifier
V
r = ( V
MT
p) / RC
For full wave rectifier
V
r = ( V
M 0.5T
p) / RC

37. P.KIRAN KUMAR,ECE DEPARTMENT 37
DIODE CLIPPERS
Clippingcircuitsbasicallylimittheamplitudeoftheinputsignaleitherbelowor
abovecertainvoltagelevel.TheyarereferredtoasVoltagelimiters,Amplitude
selectorsorSlicers.Aclippingcircuitisone,inwhichasmallsectionofinput
waveformismissingorcutortruncatedattheoutputsection.
ClippingcircuitsareclassifiedbasedonthepositionofDiode.
1.SeriesDiodeClipper
2.ShuntDiodeClipper

38. P.KIRAN KUMAR,ECE DEPARTMENT 38
SeriesDiodeclippers

39. P.KIRAN KUMAR,ECE DEPARTMENT 39
Shuntdiodeclippers

40. 40
Inelectronics,acomparator isadevicethatcompares
twovoltagesorcurrentsandoutputsadigitalsignalindicatingwhichislarger.
IthastwoanaloginputterminalsV+andV-andonebinarydigitaloutput.
Seriesdiodeclipperwithbias

41. P.KIRAN KUMAR,ECE DEPARTMENT 41

42. P.KIRAN KUMAR,ECE DEPARTMENT 42
Slicer(Clippingattwoindependentlevels)

43. P.KIRAN KUMAR,ECE DEPARTMENT 43P.KIRAN KUMAR,ECE DEPARTMENT 43
Diode equivalent circuits / models:

44. P.KIRAN KUMAR,ECE DEPARTMENT 44P.KIRAN KUMAR,ECE DEPARTMENT 44
Applications
There are many applications in which diode switching circuits are used, such as −

45. P.KIRAN KUMAR,ECE DEPARTMENT 45
Breakdown Mechanisms in a diode
Whenreversevoltageincreasesbeyondcertainvalue,largediode
currentflows,thisiscalledbreakdownofdiode,andcorresponding
voltageiscalledreversebreakdownvoltageofdiode.
Therearetwodistinctmechanismsduetowhichthebreakdown
mayoccurinthediode,theseare:
•Avalanchebreakdown
•Zenerbreakdown

46. P.KIRAN KUMAR,ECE DEPARTMENT 46
Breakdown Mechanisms in a diode
Avalanche Breakdown:
The avalanche breakdown occurs in lightly doped diodes.
The multiplication factor due to the avalanche effect is given by 1
1
M
n
V
V
BD






Where M is carrier multiplication factor
n-type silicon n=4 and For p-type n=2
V is applied reverse voltage
V
BD
is reverse breakdown voltage

47. P.KIRAN KUMAR,ECE DEPARTMENT 47
Breakdown Mechanisms in a diode
ZenerBreakdown
•Thezenerbreakdownoccursinheavilydopeddiodes.
•Forheavilydopeddiodes,thedepletionregionwidthissmall.
•Underreversebiasconditions,theelectricfieldacrossthedepletionlayerisvery
intense.Breakingofcovalentbondsduetointenseelectricfieldacrossthenarrow
depletionregionandgeneratinglargenumberofelectronsiscalledZenereffect.
•Thesegeneratedelectronsconstituteaverylargecurrentandthemechanismis
calledZenerbreakdown.
•Thediodeshavingreversebreakdownvoltagelessthan5vshowstheZener
mechanismofbreakdown.

48. P.KIRAN KUMAR,ECE DEPARTMENT 48
Zener Diode
•Zener diode is a heavily doped diode, and is designed with adequate power
dissipation capabilities to operate in the reverse breakdown region.
•The operation of the zener diode is same as that of ordinary PN diode under
forward biased condition.
•In reverse biased condition, the diode carries reverse saturation current, till the
reverse voltage applied is less than the reverse breakdown voltage.
•When the reverse voltage exceeds the reverse breakdown voltage, the current
through it changes drastically but the voltage across it remains almost constant such
a break down region is a normal operating region for a zener diode.
The symbol of zener diode is

49. P.KIRAN KUMAR,ECE DEPARTMENT 49
Zener Diode
The dynamic resistance of a zener diode is
defined as the reciprocal of the slope of the
reverse characteristics in zener region.V
z
r
z
I
z



=1/slopeofreverse
characteristicsinzenerregion
•The dynamic resistance is very small, it is of he order of few tens of ohms.

50. P.KIRAN KUMAR,ECE DEPARTMENT 50
Equivalent circuit of Zener diode

51. P.KIRAN KUMAR,ECE DEPARTMENT 51
Applications of zener diode
The various applications of zener diode are,
•As a voltage regulating element in voltage regulators.
•In various protecting circuits.
•In zener limiters i.e., clipping circuits which are used to clip off the unwanted
portion of the voltage waveform.

52. P.KIRAN KUMAR,ECE DEPARTMENT 52
Tunnel diode
•Iftheconcentrationofimpurityatomsisgreatlyincreased,say1partin10
3
thedevicecharacteristicsarecompletelychanged.
•Thenewdiodewasannouncedin1958byLeoEsaki.Thisdiodeiscalled
‘Tunneldiode’or‘Esakidiode’.
•ThebarrierpotentialVBisrelatedwiththewidthofthedepletionregionwith
thefollowingequation.
•Fromtheaboveequationthewidthofthebarriervariesinverselyasthe
squarerootofimpurityconcentration.
•Asthedepletionwidthdecreasesthereisalargeprobabilitythatanelectron
willpenetratethroughthebarrier.Thisquantummechanicalbehavioris
referredtoastunnelingandhencethesehighimpuritydensitypn-junction
devicesarecalledTunneldiodes.q N
A
V . ²
B
2

 B
2V
² .
q N
A




53. P.KIRAN KUMAR,ECE DEPARTMENT 53
Tunnel diode
Energybandstructureofheavilydopedpn-junctiondiodeunderopen
circuitedconditions

54. P.KIRAN KUMAR,ECE DEPARTMENT 54
The volt-ampere characteristics
Underappliedreversebias

55. P.KIRAN KUMAR,ECE DEPARTMENT 55
The volt-ampere characteristics
UnderappliedForwardbias

56. P.KIRAN KUMAR,ECE DEPARTMENT 56
The volt-ampere characteristics
Underappliedreversebias

57. P.KIRAN KUMAR,ECE DEPARTMENT 57
Tunnel diode
The tunnel diode symbol and small-signal model are
ApplicationsofTunneldiode:
•Itisusedasaveryhighspeedswitch,sincetunnelingtakesplaceatthespeedof
light.
•Itisusedasahighfrequencyoscillator.

58. P.KIRAN KUMAR,ECE DEPARTMENT 58
Photodiode
•The photodiode is a device that operates in reverse diode.
•The photodiode has a small transparent window that allows light to strike
one surface of the pn-junction, keeping the remaining sides unilluminated.
Thesymbolofphotodiodeis

59. P.KIRAN KUMAR,ECE DEPARTMENT 59
The volt-ampere characteristics of photodiode

60. P.KIRAN KUMAR,ECE DEPARTMENT 60
Photodiode
Advantages of Photo diodes:
•It can be used as variable-resistance device.
•Highly sensitive to the light.
•The speed of operation is very high.
Disadvantages of Photo diodes:
The dark current is temperature dependent.
Applications of photodiode:
Photodiodes are commonly used in alarm systems and counting systems.
Used in demodulators.
Used in encoders.
Used in light detectors.
Used in optical communication systems.

61. P.KIRAN KUMAR,ECE DEPARTMENT 61
Light Emitting Diode (LED)
The LED is an optical diode which emits light when forward biased, by a
phenomenon called electroluminescence.
The LEDs use the materials like Gallium Arsenide (GaAs), Gallium
Arsenide Phospide (GaAsP) or Gallium Phospide (GaP). These are the
mixtures of elements Ga,As,P.
The symbol of LED is

62. P.KIRAN KUMAR,ECE DEPARTMENT 62
LED Working Principle
•WhenanLEDisforwardbiased,theelectronsandholesmovetowardsthe
junctionandrecombinationtakesplace.
•Asaresultofrecombination,theelectronslyingintheconductionbandsof
n-regionfallintotheholeslyinginthevalancebandofp-region.
•Thedifferenceofenergybetweentheconductionbandandthevalance
bandisradiatedintheformoflightenergy.
•Theenergyreleasedintheformoflightdependsontheenergy
correspondingtotheforbiddengap.Thisdeterminesthewavelengthofthe
emittedlight.
•Thewavelengthdeterminesthecolorofthelightandalsodetermines
whetherthelightisvisibleorinvisible(infrared).

63. P.KIRAN KUMAR,ECE DEPARTMENT 63
LED Working Principle
•The color of the emitted light depends on the type of material used.
Gallium Arsenide (GaAs) ---Infrared radiation (invisible)
Gallium Phospide (GaP) ---Red or Green
Gallium Arsenide Phospide (GaAsP) ---Red or Yellow.
•The brightness of the emitted light is directly proportional to the forward
bias current.

64. P.KIRAN KUMAR,ECE DEPARTMENT 64
Output characteristics of LED
Typical output characteristics for LED
Process of electro luminescence

65. P.KIRAN KUMAR,ECE DEPARTMENT 65
Light Emitting Diode (LED)
Advantages of LEDs:
•LEDs are small in size.
•LEDs are fast operating devices.
•LEDs are light in weight.
•LEDs are available in various colors.
•The LEDs have long life.
•The LEDs are cheap and readily available.
•LEDs are easy to interface with various other electronic circuits.
Disadvantages of LEDs:
•Needs large power for the operation.
•The characteristics are affected by the temperature.

66. P.KIRAN KUMAR,ECE DEPARTMENT 66
Light Emitting Diode (LED)
ApplicationsofLEDs:
•TheLEDsareusedinallkindsofvisualdisplaysi.e.,seven
segmentdisplaysandalphanumericdisplays.Suchdisplays
arecommonlyusedinmultimeter,calculator,watchesetc.
•LEDsarealsousedinopticaldevicessuchasoptocouplers.
Theyarealsousedinburglaralarmsystems.