MOS circuit

Discussion in 'Homework Help' started by u-will-neva-no, Apr 30, 2011.

  1. u-will-neva-no

    Thread Starter Member

    Mar 22, 2011
    230
    2
    Attached is my Picasso drawing of the MOS circuit :) I want to be able to understand the answer for the truth table of this circuit.

    The N-substrate also goes to 0V

    The truth table is as follows:

    Va Vb Vo
    0V 0V +5V
    0V +5V 0V
    +5V 0V +5V
    +5V +5V 5V



    More specifically, I do not understand when the first N-gate to the right is getting 5V or 0V, due to the input of the connecting being some kind of function of the voltage just below the resistor. Thankyou!
     
  2. u-will-neva-no

    Thread Starter Member

    Mar 22, 2011
    230
    2
    woops, the circuit attached is a TTL circuit, I have converted the question from a mos to TTL and am happy to draw the MOS configuration if necessary!
     
  3. designnut

    Member

    Apr 21, 2011
    33
    1
    The second dual gate conducts only if botth inputs are +. This happeens when a is 0, B is plus. the output V0 is then 0.
     
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  4. u-will-neva-no

    Thread Starter Member

    Mar 22, 2011
    230
    2
    Would you be able to explain to me what happens at each instance? For example...i picture that when vA=0V and vB=0V, the gate on the left stays open and the bottom right gate is also open..Im not sure how the top right gate is affected in all input cases..
     
  5. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    I redrawn your diagram.
    And lets try analysis the circuit for
    VA = 0V and VB = 0 V.
    Since VA is equal 0V so T1 is OFF and T3 is also off.
    T2 will be "ON" but there is no path to GND for T2 current to flow (because T3 is "OFF").
    So Vo = Vdd = 5V
     
    Last edited: May 1, 2011
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  6. u-will-neva-no

    Thread Starter Member

    Mar 22, 2011
    230
    2
    Ahh thankyou. Would you also be able to explain the last three combinations...more in particular when vA = 5V and vB =0V and also when Va=5v and vb = 5v?...I am still struggling with these two situations.
     
  7. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Well i give you a hint.
    When MOSFET's are "ON" treat them as short circuit.
    And when MOS are "OFF" treat them as a open circuit.
     
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  8. u-will-neva-no

    Thread Starter Member

    Mar 22, 2011
    230
    2
    oh I see! Thankyou very much!!
     
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