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    DSD LogicFamilies

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    ibiiuouj
    TTL (Transistor-Transistor Logic) is a logic family of integrated circuits that uses transistors to perform logic functions. There are several TTL subfamilies with different characteristics. Standard TTL gates were constructed with varying resistor values to achieve lower power dissipation or higher speeds. Later subfamilies like Schottky TTL and low-power Schottky TTL further optimized these tradeoffs between power and speed. TTL gates can have different output configurations like totem-pole, open-collector, or three-state outputs.

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    DSD LogicFamilies

    Uploaded by

    ibiiuouj
    17 views32 pages
    TTL (Transistor-Transistor Logic) is a logic family of integrated circuits that uses transistors to perform logic functions. There are several TTL subfamilies with different characteristics. Standard TTL gates were constructed with varying resistor values to achieve lower power dissipation or higher speeds. Later subfamilies like Schottky TTL and low-power Schottky TTL further optimized these tradeoffs between power and speed. TTL gates can have different output configurations like totem-pole, open-collector, or three-state outputs.

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    DSD-LogicFamilies

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    TTL (Transistor-Transistor Logic) is a logic family of integrated circuits that uses transistors to perform logic functions. There are several TTL subfamilies with different characteristics. Standard TTL gates were constructed with varying resistor values to achieve lower power dissipation or higher speeds. Later subfamilies like Schottky TTL and low-power Schottky TTL further optimized these tradeoffs between power and speed. TTL gates can have different output configurations like totem-pole, open-collector, or three-state outputs.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    17 views32 pages

    DSD LogicFamilies

    Uploaded by

    ibiiuouj
    TTL (Transistor-Transistor Logic) is a logic family of integrated circuits that uses transistors to perform logic functions. There are several TTL subfamilies with different characteristics. Standard TTL gates were constructed with varying resistor values to achieve lower power dissipation or higher speeds. Later subfamilies like Schottky TTL and low-power Schottky TTL further optimized these tradeoffs between power and speed. TTL gates can have different output configurations like totem-pole, open-collector, or three-state outputs.

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    of 32

    TTL Logic Family

    Introduction — Logic IC
     Logic Family : A collection of different IC’s that have similar
    circuit characteristics
     A circuit configuration or approach used to produce a type of
    digital integrated circuit.
     Consequence: different logic functions, when fabricated in the
    form of an IC with the same approach, or in other words
    belonging to the same logic family, will have identical electrical
    characteristics.
     the set of digital ICs belonging to the same logic family are
    electrically compatible with each other
    Common Characteristics of the Same
    Logic Family

     Supply voltage range, speed of response, power dissipation,


    input and output logic levels, current sourcing and sinking
    capability, fan-out, noise margin, etc.
     Consequence: choosing digital ICs from the same logic
    family guarantees that these ICs are compatible with
    respect to each other and that the system as a whole
    performs the intended logic function.

    3
    Integration Levels

    • Gate/transistor ratio is roughly 1/10


    – SSI < 12 gates/chip
    – MSI < 100 gates/chip
    – LSI …1K gates/chip
    – VLSI …10K gates/chip
    – ULSI …100K gates/chip
    – GSI …1Meg gates/chip

    4
    Moore’s Law

     In 1965, Gordon Moore predicted that the number of


    transistors that can be integrated on a die would double
    every 18 to 14 months
     i.e., grow exponentially with time
     Considered a visionary – million transistor/chip barrier
    was crossed in the 1980’s
     2300 transistors, 1 MHz clock (Intel 4004/4040) - 1971
     42 Million transistors, 2 GHz clock (Intel P4) - 2001
     140 Million transistors, (HP PA-8500)
    IC digital logic families
     RTL （Resistor-transistor logic）
     DTL （Diode-transistor logic）
     TTL （Transistor -transistor logic）
     ECL （Emitter-coupled logic）
     MOS （Metal-oxide semiconductor）
     CMOS （Complementary Metal-oxide semiconductor）
    Fan-In
     Number of input signals to a gate
     Not an electrical property
     Function of the manufacturing process

    NAND gate with a


    Fan-in of 8
    Fan-Out
     A measure of the ability of the output of one gate to drive the
    input(s) of subsequent gates
     Usually specified as standard loads within a single family
     e.g., an input to an inverter in the same family
     The maximum number of logic inputs (of the same logic
    family) that an output can drive reliably is called the fan-
    out.
    Logic Level and Voltage Range
     Typical acceptable voltage ranges for positive logic 1 and logic 0 are
    shown below
     A logic gate with an input at a voltage level within the
    ‘indeterminate’ range will produce an unpredictable output level.

    5.0V
    Logic 1

    2.5V
    Indeterminate
    0.8V
    Logic 0
    0V
    TTL
    Noise Margin
    Noise margin:The unwanted signals are referred to as noise
     It is the limit of a noise voltage which may be present without impairing the
    proper operation of the circuit.
     Manufacturers 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.
     Noise margin is the maximum noise added to an input signal of a digital circuit
    that does not cause an undesirable change in the circuit output
    Speed: Rise & Fall Times
     Rise Time
     Time from 10% to 90% of signal, Low to High
     Fall Time
     Time from 90% to 10% of signal, High to Low

    rise time fall time

    10% 90% 90% 10%


     The average transition-delay time for the signal to propagate from
    input to output when the binary signal changes in value
     It is the time delay between the specified voltage points
    on the input and output waveforms.
     Propagation delays are separately defined for LOW-to-
    HIGH and HIGH-to-LOW transitions at the output. In
    addition, we also define enable and disable time delays
    that occur during transition between the high-impedance
    state and defined logic LOW or HIGH states.

    12
    TPD,HL TPD,LH

    TPD,HL – input-to-output propagation delay from HI to LO output


    TPD,LH – input-to-output propagation delay from LO to HI output

    13
     The power dissipation parameter for a logic family is
    specified in terms of power consumption per gate and is
    the product of supply voltage VCC and supply current
    ICC
     The power needed by the gate, Expressed in mW
    Power Dissipation
     Static
     I2R losses due to passive components, no input signal
     Dynamic
     I2R losses due to charging and discharging capacitances through
    resistances, due to input signal
    Power dissipation
    I CCH + I CCL
    I CC (avg ) =
    2
    PD (avg ) = I CC (avg ) × VCC
    Feature of BJT
     BJT
     npn or pnp
     Si or Ge
     Si is used mainly
     npn is most popular
    Typical npn Transistor Parameters

    Region VBE (V) VCE (V) Current


    Relation
    Cutoff < 0.6 Open IB=IC=0
    circuit
    Active 0.6-0.7 > 0.8 IC =hFEIB

    Saturation 0.7-0.8 0.2 IB ≥IC/hFE


    Transistor-Transistor Logic (TTL)
     The original basic TTL gate was a slight improvement over the
    DTL gate.
     There are several TTL subfamilies or series of the TTL technology.
     Has a number start with 74 and follows with a suffix that
    identifies the series type, e.g 7404, 74S86, 74ALS161.
     There are many versions or families of TTL

     Standard TTL.

     High Speed TTL

     Low Power TTL.

     Schhottky TTL.
     As such all the families of TTL have three configuration for outputs.

     Totem - Pole output.

     Open Collector Output.

     Tristate Output.
     TTL is slight improvement over the DTL.
     The standard TTL gate was constructed with different resistor
    values to produce gates with lower dissipation or higher speed.
     The propagation delay of a saturated logic family depends on
    largely two factors: Storage Time and RC time constants.
     Reducing the ST decreases the PD.
     Reducing resistor values in the circuit reduces the RC time
    constants and decreases PD.
     The trade off is a higher power dissipation because lower
    resistances draw more current from the power supply.
     Speed of gate is inversely proportional to PD.
     In the low power TTL gate the resistor values are higher than in
    the standard gate to reduce the Power dissipation, but PD is
    increased.
     In the high-speed TTL gate, resistor values are lowered to reduce
    the PD, but the power dissipation is increased.
     The Schottky TTL removes the storage time of transistor by
    preventing them from going into saturation, which increases the
    speed without increasing the power dissipation .
     The low-power Schottky TTL scarifies some speed for reduced
    power dissipation.
     It is about equal to standard TTL in PD but has only one-fifth
    the power dissipation.
     It has the best speed-power product.
    Open-collector TTL Gate
     Modified circuit of DTL gate.
     Multiple emitters in transistor Q1 are connected to the
    inputs.
     The voltage levels for the circuit are 0.2 V for the low
    level and from 2.4 to 5 V for the high level.
     The basic circuit is a NAND gate.
    Wired-AND of Two Open-Collector
    TTL Gate with Totem-Pole Output
    Schottky TTL Gate
    Three-state TTL Gate
    Transistor-Transistor Logic Families
     Transistor-Transistor Logic Families:
     74L Low power
     74H High speed
     74S Schottky
     74LS Low power Schottky
     74AS Advanced Schottky
     74ALS Advance Low power Schottky
    TTL Subfamilies

    31
    Comparison of Logic Families

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