Logic Function with transistors

Discussion in 'Homework Help' started by AD633, Jun 23, 2013.

  1. AD633

    Thread Starter Member

    Jun 22, 2013
    96
    1
    Hi,

    Consider the circuit of Figure 3 where the transistors operate in a regime switching (cut / saturation).

    Complete the table to the side and say what logical function is implemented by the circuit. Justify the values​​, presenting the state of conduction of each transistor.


    When we have V1 = V2 = +5 V and +5 V.

    T1:<br />
        VCE1=Vcc-Rc1*Ic<br />
        VCE1=10-(5*10^3)*Ic

    I don't know Ic and i can not determine Ib because i also dont know the value of the base resistance Rb

    5=(Rb??)*Ib+Vbe

    Is there any other way for determing Ic?

    Thanks
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    But why you need Ib and Ic current? You have been told that BJT work only in two regions of operation. The cut-off region and saturation region. So if for example V1 = +5V, T1 is in saturation region Vce1 = 0V And T3 will be OFF (cut-off) regardless T2 state.
     
  3. AD633

    Thread Starter Member

    Jun 22, 2013
    96
    1
    So its fairly simple to determine what is the logic function implemented by the circuit:

    V1 = V2 = +5 V and +5 V

    VCE1=0 V and VCE2=0 V

    V1 =+5 V and V2= 0 V


    VCE1=0V and VCE2=+VCC

    V1 =0 V and V2=+5 V


    VCE1=+VCC and VCE2=0 V

    V1 =0 V and V2=0 V


    VCE1=+5V and VCE2=+5 V

    So i think that the logic function implemented by the circuit is a NOT.
     
  4. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    Good so far.

    That would be impossible

    Not quite.

    1) Why would a NOT function have two inputs?
    2) Why are you ignoring t3?
     
  5. AD633

    Thread Starter Member

    Jun 22, 2013
    96
    1

    Yes it should be, VCE1=0V and VCE2= 0V

    I did not understand this.Are you saying that it should be

    VCE1=+VCC-(Rc1)*(Ic1sat) and VCE2=0 V

    Yes it would not make much sense :)

    I forgot about the NMOS.In a NMOS transistor we need to have a positive Vgs potential so that we get a high sinal in the output right?

    The logic function is a NAND?
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    Look at the circuit diagram and notice that if T1 is in cut-off And T2 is in saturation, we have two Rc resistors connected in series.
    Vc2 = 0V and Vce1 = ??


    No, the NMOS work just like a inverter. Vgs = 5V---> Vds --->0V
     
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