Flip Flop Triggering on Rising Edge, Not falling edge as it should

Discussion in 'General Electronics Chat' started by imzack, Feb 5, 2015.

  1. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    I have a flip flop at I have set up so it only cares about falling edges. I have a couple units however that when they get a little bit warmer, they start to trigger on the rising edge of the clock line. Any ideas on what is going on? I have looked at the scope trace, and zoomed in, the clock signal is going from 0 to 5 volts, with little time inbetween (aka 2v, to 3v, to 4v). Somewhere at around 3 volts though, the JK Flip Flop triggers on the rising edge instead of the falling edge as it should be. Why does the flip flop think the rising edge is a falling edge? Also, why does it behave this way when its warm, but if I try to cool the unit down a few degrees the unit acts as excepted?

    Thanks
     
  2. Reloadron

    Active Member

    Jan 15, 2015
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    A drawing would be nice? Can you post a drawing of the circuit?

    Ron
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    A drawing would be awfully nice.

    Where does the clock signal come from?

    My initial guess is that you are deriving your clock from a source that is glitching and the flip flop, when warm, is fast enough to respond to lower energy glitch signals than it can when it is cool.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Which flip-flop? Part number?

    Noise on the clock signal? What is generating the clock signal? What is the rise time and fall time of the clock signal?
     
  5. imzack

    Thread Starter Active Member

    Nov 3, 2010
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    Sorry about the delay on this. But I believe it to be how fast the rising and falling edges are of the clock signal.

    What inside the JK Flip Flop dictates how slow of a rising and falling edge time that is acceptable?
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    It can be any number of things -- it all depends on the details of the design. If it's CMOS, the details of the transistor thresholds plays a big role because they determine the degree of shoot through current you get and also the degree to which nodes have to act as charge-storage nodes during the transition.
     
  7. imzack

    Thread Starter Active Member

    Nov 3, 2010
    50
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    Thank you for your reply!

    That sounds above my head; If I was interested in reading more about this, do you have any suggested sites or links?

    Thanks
     
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