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Difference between TTL and CMOS

Discussion in 'Electronic Basics' started by Nick, Jan 13, 2006.

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  1. Nick

    Nick Guest

    Hi,

    What is the difference between TTL and CMos

    Thanks and Rgards,

    Nick
     
  2. Bill Bowden

    Bill Bowden Guest

    What is the difference between TTL and CMos


    Advantages of CMOS over TTL:

    1. Operates on a wider supply voltage (2 to 15 volts).
    Exception is 74HC CMOS limited to (2 to 7 volts).

    2. Uses much less power, can operate on a small battery for a year or
    so.

    3. Output swings the full supply voltage range.

    4. Input switches at half the supply voltage for better noise immunity.

    5. Input impedance is much higher so it doesn't load the driving
    circuit.

    6. 74HC CMOS can supply 25mA of output current, both source and sink.

    -Bill
     
  3. Noway2

    Noway2 Guest

    The two families utilize different types of transistors in their
    construction, Bipolar Junction transistors for TTL and Field Effect
    Transistors are used for the CMOS. There are various types of both
    transistors, but one common way to categorize them is wether they are N
    or P devices, NPN and PNP for bipolar and NMOS and PMOS for the CMOS,
    where the N and P refers to the element used to dope the silicon. The
    MOS stands for Metalic Oxide Semiconductor, which is a very thin high
    valued insulator that is used to create the the very low input current
    of CMOS devices. The C in CMOS stands for complementary, which means
    that both N and P transistors have been fabricated together to
    implement the logic. This allows the rail to rail 0 - 5 volt output
    swings achievable with CMOS.

    A bipolar transistor can be considered as a current driven switch where
    the FET can be viewed as a voltage controlled switch. This factor
    comes into play in that it is responsible for the different HIGH and
    LOW logic voltages and influences how and when TTL and CMOS devices can
    be connected together.

    While Bill's post indicated a number of advantages of CMOS, mostly with
    regards to digital logic, when it comes to analog performce, such as an
    amplifier or ADC circuit, bipolar (TTL) has some advantages. Most
    notibly, bipolar based amplifiers and transistors can often times
    achieve a higher gain and operate at a much lower noise level.
     
  4. Nick

    Nick Guest

    Hi,

    Thanks for the info. thats a lots of stuff to read.. I hope i can
    understand the above.

    Thanks again..

    Nick.
     
  5. If you're going to construct a mixed TTL/CMOS-circuit, this page might be
    of help:

    http://www.interfacebus.com/voltage_threshold.html
     
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