2-bit domino counter without static latches

Discussion in 'Homework Help' started by Sarengo, Apr 5, 2013.

  1. Sarengo

    Thread Starter New Member

    Apr 5, 2013
    3
    0
    Hello,

    I'm trying to build a 2-bit domino counter without static latches. A 2-bit counter can be implemented with 2 J-K flip flops but that wouldn't meet the requirement. Is it possible to make a dynamic J-K flip flop?

    Assume the JKFF logic is the one with two AND3 gates fed into two NOR2 gates. If I were to make these into dynamic gates, and then into domino logic by feeding them into static inverters, would this work to make a "dynamic JKFF," hence a dynamic latch?

    Would the precharge/evaluate phases of the dynamic logic be rendered incorrect through the feedback of the Q and Qnot signals required for the JKFF?

    Else: Any other ideas on how to solve the original problem of a 2-bit domino counter without static latches?

    Thanks in advance!

    ~Sarengo
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    I know next to nothing about domino logic, but isn't it intended for combinatorial logic and not sequential logic?

    I have absolutely no idea what you are talking about here.
     
  3. Sarengo

    Thread Starter New Member

    Apr 5, 2013
    3
    0
    The JKFF circuit I am referring to is:
    http://sub.allaboutcircuits.com/images/04196.png

    I was attempting to build the below linked 2-bit counter with the JKFF by turning all CMOS gates to domino gates - hence avoiding the restriction of static latches (as I was thinking it would be a dynamic latch):
    http://dev.epubbud.com/uploads/4/0/3/4032781/images/04347.png

    Upon further thought to my question, a dynamic latch is a paradox anyway, as a latch is supposed to hold values and dynamic logic is transcient (ie. a logic 1 will eventually fall to logic 0 as the capacitances in the circuit discharge). So this probably isn't the way to go for a solution.

    Domino logic can be thought of as a dynamic gate followed by a static inverting stage.
    http://en.wikipedia.org/wiki/Domino_logic

    So a 2-bit domino counter would imply using dynamic gates/stages followed by inverters to obtain my function. However, a counter relies on the previous output value so I would need a feedback loop. But the restriction is that I cannot use static latches to hold values so I'm at a loss as to what options I have...

    Using feedback loops with dynamic gates completely throws the logic out the window...anyone have suggestions or thoughts?

    ~Sarengo
     
  4. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    In the future, if you are going to make reference to a paritcular circuit, please post the circuit you are refering to. We are not mind readers.

    The notion of a dynamic latch is not a contradiction. Just as dynamic memory isn't. It just means that the stored value has to be refreshed periodically or it will be lost.

    But I think you are going to need to use a latch, be it dynamic or static, to hold your value so that you can control what signal is fed back and ensure that you don't end up with a race condition.

    Also, I think you might well find that, in general, dynamic circuits do not lend themselves well to anything other than on-chip designs. I could be wrong, but my guess is that you need pretty well characterized parasitics and propagation delays in order to get them to work reliably.
     
  5. Sarengo

    Thread Starter New Member

    Apr 5, 2013
    3
    0
    Yes, I apologize in hindsight. I had been staring at this for too long it seems.

    Yes, this is why I am asking for ideas on how to achieve this. I cannot use a static latch by requirement, so it must be a dynamic latch. However, by the time the Q and Qnot are fed back to the inputs as per a flip flop, I've already lost my stored value, which was why I was thinking it was a no-go. Is there another way to dynamically latch this that I'm not seeing...

    If the whole circuit precharges in 1 phase, what is saving my state until the next charge...the domino effect from the inverters?

    ~Sarengo
     
Loading...