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AND gate output

Discussion in 'Electronic Basics' started by novice, Jul 6, 2006.

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  1. novice

    novice Guest

    If suppose the inputs of amplitude X and 2X are applied to the
    2-input AND gate then what would be the amplitude of output ?

    Thanks a lot in advance
  2. Simoc

    Simoc Guest

    And-gates are digital gates, so you can't input analog signal to them.
    In digital system, there are just a low-level, which is usually 0V, and
    a high-level, which is some voltage depending on the system. So you
    must know what is the high level voltage in your and-gate. If it's a
    basic TTL-chip, it's 5V. So you can't input any other amplitudes than
    0V or 5V.

    If both of its inputs are low (=have 0V on them), the output will be
    low (0V)

    If one of its inputs is low (0V) and the other is high (5V), the output
    will be low (0V)

    If both of its inputs are high (5V) then the output will be high (5V).

    That's why is it AND-gate, as the input 1 AND input 2 must both be high
    to get the output going high.
  3. novice

    novice Guest

    Thanks a lot simoc for your valuable response.But if 4.8V and 5V are
    given as inputs then what would be the output? 4.8V is also considered
    as High.Right?
  4. Ralph Mowery

    Ralph Mowery Guest

    While the voltage may vary by a few tenths of a volt or so, digital logic
    only has two states (well if you concider an undefined state 3 ) high and
    low. Anything from about 0 to .8 is a low and from 2 to 5 is a high. The
    area between about .8 and 2 is undefined and should not be in a digital
    circuit . All the above should be for a 5 volt TTL circuit. Other voltages
    and types of ICs will be similar in the way they work.

    After all that, if you have an input gate with many inputs and they are all
    high or low, the output will still be almost the same voltage, either the
    normal high or low.
  5. Bob

    Bob Guest

    You need to look at the specs for a particular logic standard. Are you
    asking about:

    4000 family CMOS
    LVCMOS 3.3V
    LVCMOS 2.5V
    SSTL 2.5V
    SSTL 1.8V
    HSTL 1.8V
    HSTL 1.5V
    which one???

    Each standard will state, for inputs and outputs (a separate set of values
    for each) --
    max voltage for a '0'
    min voltage for a '1'
    along with many other characteristics.

    Since you mentioned 4.8V and 5V, I'm assuming you're talking about TTL. For
    TTL (commercial grade), an input sees a '0' if the voltage is less than
    0.8V, and sees a '1' if the voltage is higher than 2.0V. Outputs (for a
    given max load) will put out max of 0.4V for a '0', and minimum of 2.4V for
    a '1'.

    Don't be afraid to open some datasheets. There is really no other way to
    learn the specifics

  6. novice

    novice Guest

    If suppose I take TTL AND gate.Then both 4.8V and 5V are considered as
    high.Obviously the AND output would be High.Now please tell me whether
    the output will be 4.8V or 5V.
    Thanks a lot in advance
  7. John Fields

    John Fields Guest

    Please bottom post.

    Bob already gave you the answer, (shown below) and it's that the
    output voltage for a TTL "high" can be anywhere between 2.4V and 5V
    for a supply voltage of 5V.

  8. Simoc

    Simoc Guest

    Please bottom-post, like mentioned, meaning that put your reply _below_
    the quote, NOT ABOVE.

    But then the answer :) It's usually nearly the operating voltage which
    you input to the Vcc-pin of the chip. And it should be something about
    5V, within the limits of its tolerance (I don't remember, see the
    datasheet, although the 4.8V will be within the tolerance).

    But actually it doesn't probably matter anyhow, as probably nothing
    that will be fed by its output will "care" about such low (0.2V)
  9. Alan B

    Alan B Guest

    You are trying to drink whiskey from a bottle of wine. Analog circuits
    deal with magnitudes, digital circuits deal with states. The magnitude of
    the output of an analog circuit is dependent upon the magnitudes of the
    inputs. The state of the output of a digital circuit is dependent upon the
    states of the inputs. There is no direct relationship between the
    magnitudes of the inputs of a digital circuit and the magnitude of its
  10. Guest

    i am a novice in this area.just reply me if i am wrong
    in digital ics the output voltage if in corresponding to the
    even if dont give any inputs the output will be high unless u dont
    ground any of the pins in the case of AND gate. as ralph replied the
    voltages 2v to 5v will be considered high,
    then output will not be corresponding to the inputs but with the vcc
    which may be +5v.
    reply me if i am wrong
  11. John Fields

    John Fields Guest

  12. nitin

    nitin Guest


    thanks , i was wrong . i checked it out.
    then what about the question
    If suppose I take TTL AND gate.Then both 4.8V and 5V are
    considered as
    high.Obviously the AND output would be High.Now please tell me whether
    the output will be 4.8V or 5V.
    that novice asked. pls tell me abt
    that.thans a lot
  13. Bob

    Bob Guest

    If you cannot read and understand the previous posts then the answer is that
    you need to select a different career path. You will not be successful in
    electronics. I promise you that this is true.

  14. nitin

    nitin Guest


    hey hey hey
    i am sorry abt my mistake . u cant advice like that .
    ive introduced myself as beginner. and if the questions or answers are
    wrong, just justify urself.we are here to discuss and if u think u are
    a an expert in electronics prove urself rather than talk more.
    reply me . no thanks for ur assumption of my career in electronics.
  15. John Fields

    John Fields Guest

  16. jasen

    jasen Guest

    They already said the output will be somewhere between 2.4 an 5V.
    This is assuming it's a TTL chip, and it's being used correctly.

  17. Please try to use something resembling normal English - do not use "u"
    when you mean "you". As a native English speaker, I find that very
    distracting - I can't imagine the trouble "u" and "urself" will cause
    those for whom English is a second language.

    For bipolar TTL logic circuits, anything above 2.4 volts will be
    considered a high. I think most parts will produce 3 - 3.5 volts for
    a high, and around 0.4 volts as a low. (I've been working with this
    stuff for so long that just looking at signal levels or waveforms, I
    "know" what is "high" without having to really measure the voltage.)

    CMOS logic will produce something over 4.5 volts for a high (assuming
    5 volts power supply, and depending on the load the output is driving)

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
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    Vancouver Power Squadron:
  18. Alan B

    Alan B Guest

    Hello. There is no answer to this question:

    "Now please tell me whether the output will be 4.8V or 5V."

    You must ask a different question.
  19. nitin

    nitin Guest

    hello to everybody
    I am sorry for those who got hurt there.
    Now I am known to quite number of members.
    anyhow thanks for your replies.
    I am now clear about the TTL devices.
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