logic families
TRANSCRIPT
Logic FamiliesLogic FamiliesIntroduction & OverviewIntroduction & Overview
CSET 4650 Field Programmable Logic Devices
Dan SolarekDan SolarekDan Solarek
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Logic FamiliesLogic FamiliesLogic Family : A collection of different ICLogic Family : A collection of different IC’’s that s that have similar circuit characteristicshave similar circuit characteristicsThe circuit design of the basic gate of each logic The circuit design of the basic gate of each logic family is the samefamily is the sameThe most important parameters for evaluating and The most important parameters for evaluating and comparing logic families include :comparing logic families include :
Logic Levels Logic Levels Power Dissipation Power Dissipation Propagation delayPropagation delayNoise margin Noise margin FanFan--out ( loading )out ( loading )
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Example Logic FamiliesExample Logic FamiliesGeneral comparison or three commonly available logic General comparison or three commonly available logic families.families.
the most important to understand
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Implementing Logic CircuitsImplementing Logic CircuitsThere are several varieties of transistors There are several varieties of transistors –– the the building blocks of logic gates building blocks of logic gates –– the most important the most important are:are:
BJT (bipolar junction transistors)BJT (bipolar junction transistors)one of the first to be inventedone of the first to be invented
FET (field effect transistors)FET (field effect transistors)especially Metalespecially Metal--Oxide Semiconductor types (Oxide Semiconductor types (MOSFETMOSFET’’ss))MOSFETMOSFET’’ss are of two types: NMOS and PMOSare of two types: NMOS and PMOS
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Transistor Size ScalingTransistor Size ScalingPerformance improves as size is decreased: shorter switching time, lower power consumption.
2 orders of magnitude reduction in transistor size in 30 years.
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MooreMoore’’s Laws LawIn 1965, Gordon Moore predicted that the number of In 1965, Gordon Moore predicted that the number of transistors that can be integrated on a die would transistors that can be integrated on a die would double every 18 to 14 monthsdouble every 18 to 14 months
i.e., grow exponentially with timei.e., grow exponentially with time
Considered a visionary Considered a visionary –– million transistor/chip million transistor/chip barrier was crossed in the 1980barrier was crossed in the 1980’’ss
2300 transistors, 1 MHz clock (Intel 4004/4040) 2300 transistors, 1 MHz clock (Intel 4004/4040) -- 1971197142 Million transistors, 2 GHz clock (Intel P4) 42 Million transistors, 2 GHz clock (Intel P4) -- 20012001140 Million transistors, (HP PA140 Million transistors, (HP PA--8500)8500)
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MooreMoore’’s Law and Intels Law and Intel
From Intel’s 4040 (2300 transistors) to Pentium II (7,500,000 transistors) and beyond
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TTL and CMOSTTL and CMOSConnecting Connecting BJTBJT’’ss together gives rise to a family of logic gates together gives rise to a family of logic gates known as TTLknown as TTLConnecting NMOS and PMOS transistors together gives rise Connecting NMOS and PMOS transistors together gives rise to the CMOS family of logic gatesto the CMOS family of logic gates
BJT MOSFET(NMOS, PMOS)transistor types
TTL CMOSlogic gate families
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Electrical Parameters And Electrical Parameters And Interpretation Of Data SheetsInterpretation Of Data Sheets
Voltages and CurrentsVoltages and CurrentsNoise MarginNoise MarginPower DissipationPower DissipationPropagation DelayPropagation DelaySpeedSpeed--Power ProductPower ProductFanFan--In, FanIn, Fan--OutOutComparison of Logic FamiliesComparison of Logic FamiliesInterpretation of Data SheetsInterpretation of Data Sheets
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Electrical CharacteristicsElectrical Characteristics
CMOSCMOSlower power consumptionlower power consumptionsimpler to makesimpler to makegreater packing densitygreater packing densitybetter noise immunity
TTL TTL faster (some versions)faster (some versions)strong drive capabilitystrong drive capabilityruggedrugged
better noise immunity
• Complex IC’s contain many millions of transistors• If constructed entirely from TTL type gates would melt• A combination of technologies (families) may be used• CMOS has become most popular and has had greatest development
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Voltage & CurrentVoltage & CurrentFor a HighFor a High--state gate driving a second gate, we define:state gate driving a second gate, we define:
VVOHOH (min), high(min), high--level output voltage, the minimum voltage level that a logic level output voltage, the minimum voltage level that a logic gate will gate will produce as a logic 1 outputproduce as a logic 1 output..VVIHIH (min), high(min), high--level input voltage, the minimum voltage level that a logic level input voltage, the minimum voltage level that a logic gate will gate will recognize as a logic 1 inputrecognize as a logic 1 input. Voltage below this level will not be . Voltage below this level will not be accepted as high.accepted as high.IIOHOH, high, high--level output current, current that flows from an output in the llevel output current, current that flows from an output in the logic ogic 1 state under specified load conditions.1 state under specified load conditions.IIIHIH, high, high--level input current, current that flows into an input when a loglevel input current, current that flows into an input when a logic 1 ic 1 voltage is applied to that input.voltage is applied to that input.
Ground
VIHVOH
I OH I IHTest setup for measuring values
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Voltage & CurrentVoltage & CurrentFor a LowFor a Low--state gate driving a second gate, we state gate driving a second gate, we define:define:
VVOLOL (max), low(max), low--level output voltage, the maximum voltage level level output voltage, the maximum voltage level that a logic gate will that a logic gate will produce as a logic 0 outputproduce as a logic 0 output..VVILIL (max), low(max), low--level input voltage, the maximum voltage level level input voltage, the maximum voltage level that a logic gate will that a logic gate will recognize as a logic 0 inputrecognize as a logic 0 input. Voltage above . Voltage above this value will not be accepted as low.this value will not be accepted as low.IIOL OL , low, low--level output current, current that flows from an output level output current, current that flows from an output in the logic 0 state under specified load conditions.in the logic 0 state under specified load conditions.IIIL IL , low, low--level input current, current that flows into an input when level input current, current that flows into an input when a logic 0 voltage is applied to that input.a logic 0 voltage is applied to that input.
Inputs are connected to Vccinstead of Ground
Ground
V ILV OL
I OL I IL
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Electrical CharacteristicsElectrical Characteristics
Important characteristics are:Important characteristics are:
VVOHminOHmin min value of output recognized as a min value of output recognized as a ‘‘11’’VVIHminIHmin min value input recognized as a min value input recognized as a ‘‘11’’
VVILmaxILmax max value of input recognized as a max value of input recognized as a ‘‘00’’VVOLmaxOLmax max value of output recognized as a max value of output recognized as a ‘‘00’’
Values outside the given range are not allowed.Values outside the given range are not allowed.logic 0logic 0
logic 1logic 1
indeterminateindeterminateinput voltageinput voltage
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Typical acceptable voltage ranges for positive logic 1 and Typical acceptable voltage ranges for positive logic 1 and logic 0 are shown belowlogic 0 are shown belowA logic gate with an input at a voltage level within the A logic gate with an input at a voltage level within the ‘‘indeterminateindeterminate’’ range will produce an unpredictable output range will produce an unpredictable output level.level.
Logic Level & Voltage RangeLogic Level & Voltage Range
Logic 1
Logic 0
5.0V
0V
2.5VIndeterminate
0.8V
TTL
Logic 1
Logic 0
5.0V
Indeterminate
0V
1.5V
CMOS
3.5V
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Noise MarginNoise MarginManufacturers specify voltage limits to represent the logical 0 or 1. These limits are not the same at the input and output sides.
For example, a particular Gate A may output a voltage of 4.8V when it is supposed to output a HIGH but, at its input side, it can take a voltage of 3V as HIGH.
In this way, if any noise should corrupt the signal, there is some margin for error.
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Noise MarginNoise MarginIf noise in the circuit is high enough If noise in the circuit is high enough it can push a logic 0 up or drop a it can push a logic 0 up or drop a logic 1 down into the indeterminate logic 1 down into the indeterminate or or ““illegalillegal”” regionregionThe magnitude of the voltage The magnitude of the voltage required to reach this level is the required to reach this level is the noise marginnoise marginNoise margin for logic high is:Noise margin for logic high is:
NNMHMH = = VVOHminOHmin –– VVIHminIHmin
VOHmin
VIHmin
VILmax
VOLmaxlogic 0logic 0
logic 1logic 1
indeterminateindeterminateinput voltageinput voltage
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Noise MarginNoise MarginDifference between the worst case output voltage of Difference between the worst case output voltage of one stage and worst case input voltage of next stage one stage and worst case input voltage of next stage Greater the difference, the more unwanted signal that Greater the difference, the more unwanted signal that can be added without causing incorrect gate can be added without causing incorrect gate operationoperation
NMNMhighhigh = = VVOHminOHmin -- VVIHminIHmin
NMNMlowlow = = VVILmaxILmax -- VVOLmaxOLmax
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Worked ExampleWorked ExampleGiven the following parameters, calculate the Given the following parameters, calculate the noise margin of 74LS series.noise margin of 74LS series.
Parameter 74LSVIH(min) 2VVIL(max) 0.8VVOH(min) 2.7VVOL(max) 0.4V
Solution:High Level Noise Margin, VNH = VOH (min) - VIH (min)=2.7V-2.0V=0.7VLow Level Noise Margin, VNL = VIL (max) - VOL (max)=0.8V-0.4V=0.4V
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Noise Margin & Noise ImmunityNoise Margin & Noise ImmunityNoise immunity of a logic circuit refers to the circuitNoise immunity of a logic circuit refers to the circuit’’s ability s ability to tolerate noise voltages on its inputs. to tolerate noise voltages on its inputs. A quantitative measure of noise immunity is called A quantitative measure of noise immunity is called noise noise marginmarginHigh Level Noise Margin, VHigh Level Noise Margin, VNHNH = V= VOHOH (min) (min) -- VVIHIH (min)(min)Low Level Noise Margin, VLow Level Noise Margin, VNLNL = V= VILIL (max) (max) -- VVOLOL (max)(max)
Logic 1
Logic 0Logic 0
Logic 1VOH (min)
VOL (max)
VIH (min)
VIL (max)
VNH
VNL
Output Voltage Ranges Input Voltage Ranges
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Further Important CharacteristicsFurther Important CharacteristicsThe The propagation delay propagation delay ((ttpdpd) which is the time ) which is the time taken for a change at the input to appear at the taken for a change at the input to appear at the outputoutputThe The fanfan--outout, which is the maximum number of , which is the maximum number of inputs that can be driven successfully to either inputs that can be driven successfully to either logic level before the output becomes invalidlogic level before the output becomes invalid
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Speed: Rise & Fall TimesSpeed: Rise & Fall TimesRise TimeRise Time
Time from 10% to 90% of signal, Low to HighTime from 10% to 90% of signal, Low to HighFall TimeFall Time
Time from 90% to 10% of signal, High to LowTime from 90% to 10% of signal, High to Low
rise time
10% 90% 90% 10%
fall time
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Speed: Propagation DelaySpeed: Propagation DelayA logic gate always takes some time to change statesA logic gate always takes some time to change statesttPLHPLH is the delay time before output changes from low to high is the delay time before output changes from low to high ttPHLPHL is the delay time before output changes from high to lowis the delay time before output changes from high to lowboth both ttPLHPLH & & ttPHLPHL are measured between the 50% points on the are measured between the 50% points on the input and output transitionsinput and output transitions
50%Input
Output
0
0tPHL tPLH
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Power DissipationPower DissipationStaticStatic
II22R losses due to passive components, no input signalR losses due to passive components, no input signal
DynamicDynamicII22R losses due to charging and discharging capacitances R losses due to charging and discharging capacitances through resistances, due to input signalthrough resistances, due to input signal
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SpeedSpeed--Power ProductPower ProductSpeed (propagation delay) and power consumption Speed (propagation delay) and power consumption are the two most important performance parameters are the two most important performance parameters of a digital IC.of a digital IC.A simple means for measuring and comparing the A simple means for measuring and comparing the overall performance of an IC family is the speedoverall performance of an IC family is the speed--power product (the smaller, the better).power product (the smaller, the better).For example, an IC has For example, an IC has
an average propagation delay of 10 ns an average propagation delay of 10 ns an average power dissipation of 5 an average power dissipation of 5 mWmWthe speedthe speed--power product = (10 ns) x (5 power product = (10 ns) x (5 mWmW))
= 50 = 50 picoJoulespicoJoules ((pJpJ))
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Logic Family TradeoffsLogic Family Tradeoffs
Looking for the best Looking for the best speed/power productspeed/power productttpp and Pd are normally and Pd are normally included in the data included in the data sheet for each devicesheet for each deviceOlder logic families Older logic families are the worstare the worstCMOS is one of the CMOS is one of the bestbestFPGAsFPGAs use CMOSuse CMOS
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Comparison of Logic FamiliesComparison of Logic Families
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TTL TTL -- ExampleExample SN74LS00SN74LS00Recommended operating conditionsRecommended operating conditions
VVcccc supply voltage supply voltage 5V 5V ±± 0.5 V0.5 Vinput voltages input voltages VVIHIH = 2V= 2V
VVILIL = 0.8V= 0.8V
Electrical CharacteristicsElectrical Characteristicsoutput voltage output voltage VVOHOH = 2.7V= 2.7V(worst case) (worst case) VVOLOL = 0.5V = 0.5V
max input currentsmax input currents IIIHIH = 20= 20µµAAIIILIL = = --0.4mA0.4mA
propagation delay propagation delay ttpdpd = 15 = 15 nSnS
noise margins noise margins for a logic 0 = 0.3Vfor a logic 0 = 0.3Vfor a logic 1 = 0.7Vfor a logic 1 = 0.7V
FanFan--outout 20 TTL loads20 TTL loads
5 Volt
0 Volt
0.80.5
2.02.7
InputRangefor 1
InputRangefor 0
OutputRangefor 0
OutputRangefor 1
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FanFan--InInNumber of input signals to a gateNumber of input signals to a gate
Not an electrical propertyNot an electrical propertyFunction of the manufacturing processFunction of the manufacturing process
NAND gate with a Fan-in of 8
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FanFan--OutOutA measure of the ability of the output of one gate to A measure of the ability of the output of one gate to drive the drive the input(sinput(s) of subsequent gates) of subsequent gatesUsually specified as standard loads within a single Usually specified as standard loads within a single familyfamily
e.g., an input to an inverter in the same familye.g., an input to an inverter in the same familyMay have to compute based on current drive May have to compute based on current drive requirements when mixing familiesrequirements when mixing families
Although mixing families is not usually recommendedAlthough mixing families is not usually recommended
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Current Sourcing and SinkingCurrent Sourcing and Sinking
VOH
IIH
Low
VOL
IIL
High
CurrentCurrent--source : the driving gate produces a source : the driving gate produces a outgoing currentoutgoing current
Current-sinking : the driving gate receives an incoming current
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FanFan--OutOutAn illustration of fanAn illustration of fan--out and the associated source out and the associated source and sink currentsand sink currents
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Worked ExampleWorked ExampleHow many 74LS00 NAND gate inputs can be driven How many 74LS00 NAND gate inputs can be driven by a 74LS00 NAND gate outputs ?by a 74LS00 NAND gate outputs ?
Solution:Solution:Refer to data sheet of 74LS00, the maximum values ofRefer to data sheet of 74LS00, the maximum values of
IIOH OH = 0.4mA, = 0.4mA, IIOLOL = 8mA= 8mA, I, IIHIH = 20uA, and = 20uA, and IIILIL = 0.4mA= 0.4mAHence,Hence,
fanfan--out(highout(high) = ) = IIOHOH(max(max) / ) / IIIHIH (max)=0.4mA/20uA=20(max)=0.4mA/20uA=20fanfan--out(lowout(low) = ) = IIOLOL(max(max) / ) / IIILIL(max(max)=8mA/0.4mA=20,)=8mA/0.4mA=20,the overall fanthe overall fan--out = fanout = fan--out(highout(high) or fan) or fan--out(lowout(low) whichever is lower. ) whichever is lower. Hence, overall fanHence, overall fan--out = 20out = 20
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Gate Drive Capability: FanGate Drive Capability: Fan--OutOutA logic gate can supply a maximum A logic gate can supply a maximum outputoutput currentcurrent
IIOHOH(max(max), in the high state or), in the high state orIIOLOL(max(max), in the low state), in the low state
A logic gate requires a maximum A logic gate requires a maximum inputinput currentcurrentIIIHIH(max(max), in the high state or), in the high state orIIILIL(max(max), in the low state), in the low state
Ratio of output and input current decide how many logic Ratio of output and input current decide how many logic gates can be driven by a logic gategates can be driven by a logic gate
fanfan--out(highout(high) = ) = IIOHOH(max(max) / I) / IIH IH (max)(max)fanfan--out(lowout(low) = ) = IIOLOL(max(max) / ) / IIILIL(max(max))overall fanoverall fan--out = fanout = fan--out(highout(high) or fan) or fan--out(lowout(low) whichever is lower) whichever is lower
A typical figure of fanA typical figure of fan--out is ten (10)out is ten (10)
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WiredWired--ANDANDOpen collector outputs connected together to a common pullOpen collector outputs connected together to a common pull--up resistorup resistorAny collector can pull the signal line lowAny collector can pull the signal line lowLogically an AND gateLogically an AND gate
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TriTri--State LogicState LogicBoth output transistors of totemBoth output transistors of totem--pole output are turned off pole output are turned off Usually used to bus multiple signals on the same wireUsually used to bus multiple signals on the same wireGates not enabled present highGates not enabled present high--Z to bus and therefore do Z to bus and therefore do not interfere with other gates putting signals on the busnot interfere with other gates putting signals on the bus
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TriTri--State LogicState LogicTriTri--state logic includes a switch at the outputstate logic includes a switch at the outputIn the figure below, the three states are illustrated:In the figure below, the three states are illustrated:a)a) Logic High outputLogic High outputb)b) Logic Low outputLogic Low outputc)c) High impedance (HiHigh impedance (Hi--Z) outputZ) output
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Electronic Combinational LogicElectronic Combinational LogicWithin each of these families there is a large variety of differWithin each of these families there is a large variety of different devicesent devices
We can break these into groups based on the number gates per devWe can break these into groups based on the number gates per deviceice
AcronymAcronym DescriptionDescription No GatesNo Gates ExampleExampleSSISSI SmallSmall--scale integrationscale integration <12<12 4 NAND gates4 NAND gatesMSIMSI MediumMedium--scale integrationscale integration 12 12 –– 100100 AdderAdderLSILSI LargeLarge--scale integrationscale integration 100 100 –– 10001000 68006800VLSIVLSI Very largeVery large--scale integrationscale integration 1000 1000 –– 1M1M 6800068000ULSIULSI Ultra large scale integrationUltra large scale integration > 1M> 1M 80486/8058680486/80586
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SSI DevicesSSI Devices
Each package contains a code identifying the packageEach package contains a code identifying the package
N74LS00
Manufacturers Code
N = National SemiconductorsSN = Signetics
Specification
FamilyLLSH
Member00 = Quad 2 input NAND02 = Quad 2 input Nor04 = Hex Invertors20 = Dual 4 Input NAND
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7400 Series History7400 Series History
1960s space program drove 1960s space program drove development of 7400 seriesdevelopment of 7400 series
Consumed all available devices for Consumed all available devices for internal flight computerinternal flight computer$1000 / device (1960 dollars)$1000 / device (1960 dollars)10:1 integration improvement over 10:1 integration improvement over discrete transistorsdiscrete transistors
1963 Minuteman missile forced 1963 Minuteman missile forced 7400 into mass production7400 into mass production
Drove pricing down to $25 / circuit Drove pricing down to $25 / circuit (1963 dollars)(1963 dollars)
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7400 Series Evolution7400 Series EvolutionBJT storage time reduction by using a BC Schottky diode.Schottky diode has a Vfw=0.25V. When BC junction becomes forward biased Schottky diode will bypass base current.
B
C
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Too Much of a Good Thing?Too Much of a Good Thing?FamiliesFamiliesPackagesPackagesReliability optionsReliability optionsSpeed gradesSpeed gradesFeaturesFeaturesFunctionsFunctions
An availability nightmare! >> 500K unique devices
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Different Families DonDifferent Families Don’’t all Speak t all Speak the Same Languagethe Same Language
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Sometimes Things Get Lost or Sometimes Things Get Lost or Added in the Translation*Added in the Translation*
Different families aren’t always on speaking terms with one another
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The World of TTLThe World of TTL
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Success Drives ProliferationSuccess Drives Proliferation
19602003
New families introduced based on New families introduced based on Higher performanceHigher performanceLower powerLower powerNew featuresNew featuresNew signaling thresholdNew signaling threshold
Spawned over 32 unique families!Spawned over 32 unique families!
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Success Drives ProliferationSuccess Drives ProliferationProducts introduced in the 1960 Products introduced in the 1960 are near the end of their life are near the end of their life cyclecycle
Decreasing supplier baseDecreasing supplier baseIncreasing pricesIncreasing pricesNot recommended for new Not recommended for new designsdesigns
Products considered to be Products considered to be ““maturemature”” are about 2 decades are about 2 decades into their life cycleinto their life cycle
HighHigh--volume productionvolume productionMultiple suppliersMultiple suppliersLow pricesLow prices
Newer products are only a few Newer products are only a few years into their life cycleyears into their life cycle
High performanceHigh performanceHigh level of vendor and High level of vendor and supplier supportsupplier supportNewest technologiesNewest technologiesHigher pricesHigher prices
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Characteristics: TTL and MOSCharacteristics: TTL and MOS
TTL stands for TransistorTTL stands for Transistor--Transistor LogicTransistor Logicuses uses BJTsBJTs
MOS stands for Metal Oxide SemiconductorMOS stands for Metal Oxide Semiconductoruses uses FETsFETs
MOS can be classified into three subMOS can be classified into three sub--families:families:PMOS (PPMOS (P--channel)channel)NMOS (NNMOS (N--channel)channel)CMOS (Complementary MOS, most common)
Remember:Remember:
CMOS (Complementary MOS, most common)
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TTL Circuit OperationTTL Circuit Operation
AB Y O/P
+Vcc
Q1
Q2
Q3
Q4
4K 1.6K 130R1 R2
R3
R41K
I CQ1
D3
D1 D2
A B ICQ1 Q1 Q2 Q3 Q4 Y O/P
0 0 + ON OFF OFF ON 1
0 1 + ON OFF OFF ON 1
1 0 + ON OFF OFF ON 1
1 1 - OFF ON ON OFF 0
A standard TTL NAND gate circuit
Table explaining the operation of the TTL NAND gate circuit
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TransistorTransistor--Transistor Logic FamiliesTransistor Logic FamiliesTTransistorransistor--TTransistor ransistor LLogic Families:ogic Families:
74L74L LLow powerow power74H74H HHigh speedigh speed74S74S SSchottkychottky74LS74LS LLow power ow power SSchottkychottky74AS74AS AAdvanced dvanced SSchottkychottky74ALS 74ALS AAdvance dvance LLow power ow power SSchottkychottky
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MOS Circuit OperationMOS Circuit Operation+VDD
O/P
I/P
S
D
D
S
Q
Q
1
2
I / P Q1 Q2 O / P
0 O N O F F 1
1 O F F O N 0
Table explaining the operation of the CMOS inverter circuit
A CMOS inverter circuit
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CMOS Logic FamiliesCMOS Logic Families
CMOS Logic FamiliesCMOS Logic Families4040xx/45xxxx/45xx MetalMetal--gate CMOSgate CMOS74C74C TTLTTL--compatible compatible CCMOSMOS74HC74HC HHigh speed igh speed CCMOSMOS74ACT74ACT AAdvanced dvanced CCMOS MOS --TTTL compatibleTL compatible
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CMOS Family EvolutionCMOS Family Evolution
CMOS Logic Trend: Reduction of dynamic losses (cross-conduction, capacitive charge/discharge cycles) by decreasing supply voltages:
12V→5V →3.3V →2.5V → 1.8V → 1.5V …Reduction of IC power dissipation is the key to:
lower cost (packaging)higher integrationimproved reliability
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Comparison of Logic FamiliesComparison of Logic Families
vi
vo
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Comparison Logic FamiliesComparison Logic Families
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Comparison of Logic FamiliesComparison of Logic Families
speed power product = a constant