BEE1213 Digital Electronics INTEGRATED CIRCUIT LOGIC FAMILY

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BEE1213 Digital ElectronicsINTEGRATED CIRCUIT
LOGIC FAMILY

• CHAPTER 7

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Introduction

• 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.

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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

• Stray electric and magnetic fields can induce
  voltages on the connecting wires between logic
  circuits this unwanted signal called noise
• These cause the input signal to a logic circuit
  drop below VIH (min) or rise above VIL (max)
• Noise immunity refers to the circuits ability to
  tolerate noise without causing spurious changes
  in the output voltage

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Noise Immunity (cont.)

• Figure 8-4(a) is a diagram showing the range of
  voltages that can occur at a logic circuit
  output.
• Any voltage greater than VOH(min) considered a
  logic 1
• Voltages lower than VOL (max) logic 0

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Noise Immunity (cont.)
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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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Example 8-1

• The I/O voltage specification for the standard
  TTL family are listed in the following table. Use
  these values to determine the following
• The maximum amplitude noise spike that can be
  tolerated when a HIGH output is driving an input
• The maximum amplitude noise spike that can be
  tolerated when a LOW output is driving an input

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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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Supply Voltage and Temperature 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 use
• b. Schottky TTL, 74S series
• c. Low-power Schottky TTL, 74LS Series
• d. 74AS
• e. 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

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Advanced Low Power Schottky TTL, 74ALS Series

• Improved on both speed and power dissipation

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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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Example 2

• Use table 8-6 to calculate the dc noise margin
  for all types of 74

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TTL Loading and Fan Out
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Determining the Fan Out

• How many inputs an IC output can drive
• We need to know capability of the output
• Example How many 74ALS00 NAND gate inputs can
  be driven by a 74ALS00 NAND gate output

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Example 8-6

• Refer to the data sheet on the TI CD ROM and
  determine how many 74AS20 NAND gates can be
  driven by the output of another 74AS20