bk tp.hcm 2009 dce integrated circuit logic family ©2009, ce department
TRANSCRIPT
BKTP.HCM
2009dce
INTEGRATED CIRCUIT LOGIC FAMILY
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• ICs have made digital systems more reliable by reducing the number of external interconnection from one device to another.
• ICs have reduced the amount of electrical power needed to perform a given function.
• IC cannot handle very large currents or voltages because the heat generated in such small spaces would cause temperature to rise beyond acceptable limits
• ICs are principally used to perform low-power circuit operations that are commonly called information processing.
Introduction
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Introduction
• Rapidly growth from SSI, with fewer than 12 gates per chip; through MSI, with 12 to 99 equivalent gates per chip
• Others – LSI, VLSI, ULSI and GSI
• There are some things IC cannot do – when deal with very large current
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Digital IC Terminology
• VIH (min) – High level input voltage. The minimum level required for a logical 1 at an input. Any voltage below this level will not be accepted as a HIGH by the logic circuit
• VIL (max) – The maximum input voltage for logic zero
• VOH (min) – The minimum voltage level at a logic circuit output in the logic 1 state under defined load conditions
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Digital IC Terminology (cont.)
• VOL (max) – Low level output voltage. The maximum voltage level at a logic circuit output in the logical 0 state under defined load conditions
• IIH – High level input current. The current that flows into an input when a specified high level voltage is applied to that input
• IIL – Low level input current. The current that flows into an input when a specified low level voltage is applied to that input
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Digital IC Terminology (cont.)
• IOH – High level output current
• IOL – Low level output current
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Exercise
• Describe the input and output logic for IC 7442
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Fan out
• Also known as loading factor
• Defined as the maximum number of logic inputs that an output can drive reliably
• A logic circuit that specify to have 10 fan out can drive 10 logic inputs
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Propagation delay
• Two types of propagation delay – tPLH , delay time in going from logical 0 to 1; tPHL delay from 1 to 0
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Noise Immunity
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Noise Immunity (cont.)
• The high state noise margin VNH is defined as
VNH = VOH (min) – VIH (min)
• The low state noise margin VNL is defined as
VNL = VIL (max) – VOL (max)
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Power Requirements
• Every IC need a certain power requirement to operate
• This power supply is come from the voltage supply that connected to the pin on the chip labeled VCC(TTL) or VDD(MOS)
• The amount of power require by ICs is determined by the current that it draws from the VCC
• The actual power is ICCxVCC
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Cont.
• ICC(avg) = (ICCH + ICCL)/2
• PD(avg) = ICC(avg)Xvcc
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The TTL Logic Family
FIGURE 8-7 (a) Basic TTL NAND gate; (b) diode equivalent for Q1.
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TTL NOR gate
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TTL Data sheet• In 1964, Texas Instruments corporation introduced the first line of
standard TTL ICs
• The 54/74 series, most widely used IC logic families
• The difference between 54 and 74 series is a range of temperatures
• IC number is the same with all series produce by different manufactures
• Each manufacturer however usually used the prefix that represent the special words – Texas Instrument uses the prefix SN, National semiconductor uses DM etc
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Range• 74ALS series and the 54ALS series use nominal
supply voltage (VCC) of 5V, but can tolerate a supply variation of 4.5 to 5.5V.
• 74ALS series can operate properly in ambient temperatures ranging from 0 to 70 degrees C, while the 54ALS series can handle -55 to +124 degree C.
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Voltage Levels
• Input and output voltage levels can be found on the data sheet.
• The min and max values shown are for worst case conditions of power supply, temperature and loading conditions
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TTL Series Characteristics
• We have found the type of ICs – 74, 74LS, 74ALS before
• LS – low power Schottky, ALS – advance low power Schottky
• The function is same, but the difference is on the characteristic
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TTL Data Sheet
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TTL Series Characteristics• 74 series of TTL – offers a wide variety of gates and
flip flops• Consist of:
a. Standard TTL, 74 series – no longer be useb. Schottky TTL, 74S seriesc. Low-power Schottky TTL, 74LS Seriesd. 74ASe. 74ALS and 74F
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Schottky TTL, 74S Series
• 7400 series operates using saturated switching in which many of the transistors, when conducting will be in saturated condition
• This can causes a storage time delay ts when the transistors switch from ON to OFF and effect the speed
• 74S series come to solve the speed problem• It accomplishes this by using a Schottky barrier
diode (SBD)
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Schottky TTL, 74S Series (cont.)
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Advances Schottky TTL, 74AS series
• 74AS give more advance on speed switching of TTL ICs at much lower consumption
• The comparison is shown in the following table for a NAND gate in each series
74S 74AS
Propagation delay
Power dissipation
Speed-power product
3ns
20 mW
60 pJ
1.7ns
8 mW
13.6 pJ
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74ALS Series• Improved on both speed
and power dissipation
74S 74AS
Propagation delay
Power dissipation
Speed-power product
9.5 ns
2 mW
19 pJ
4 ns
1.2 mW
4.8 pJ
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Example
• Use table 8-6 to calculate the dc noise margins for a typical 74LS IC. How does this compare with the standard TTL noise margins ?
Solution
• 74LS
VNH = VOH(min) – VIH(min)
= 2.7 – 2.0
= 0.7 V
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TTL Loading and Fan Out
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