Ripple counter transition filter & Comparator

Discussion in 'Homework Help' started by allhuber, Jan 24, 2012.

  1. allhuber

    Thread Starter New Member

    Nov 5, 2011
    12
    0
    Hi AAc,

    Hope someone can help me with this problem. I have a "a=b" comparator. "a" is the feedback of the mod10 counter while "b" is a dip switch for me choose. I tested out the circuit and had some problems. "a" & "b" are 4 bits.

    For the comparator, I did some research and came across this circuit: http://engineersworld.files.wordpress.com/2011/01/21.jpg

    The problem is when I toggle to count numbers ,2(0010), 4(0100), 6(0110), 8(1000), I get some spike. I suspect it is the propagation delay I tested same comparator with an up/down(74193) counter but the problems were different. Is there a way I can filter feedback of the counter "a" without using any IC cos. I guess it can be done with components like diodes, capacitor, resistor.

    Waveform:
    [​IMG]

    Hope some can guide me with this. Thanks ALOT!!
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    The problem with "race" would be worse with a ripple counter than with a synchronous counter. I would switch to a synchronous counter to reduce the width of the glitches.
    You can try different logic types such as CMOS or 74C, 74HC, 74HCT series in order to slow down the transitions.
    In any case, you may still end up with glitches. Try an RC filter at the output of the AND gate.
     
  3. allhuber

    Thread Starter New Member

    Nov 5, 2011
    12
    0
    Thanks for the reply. I did HPF and it works.
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    You mean LPF.
     
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