transmission gate output unstable

Discussion in 'The Projects Forum' started by robby991, Apr 13, 2009.

  1. robby991

    Thread Starter Active Member

    Dec 17, 2007
    79
    0
    Hello everyone. I have a noise issue with my CD4016BE transmission gate I am using. As can be seen in the circuit attached, I have 3 nice and clean pulse train inputs to this IC, and the outputs are connected together to one line. As I activate each gate (C1, C2, C3), I still see the pulse train at the output, however it is not clean and fluctuates. This has something to do with the outputs being connected to each other I think, although I do not know how to clean this up. Does anyone have any suggestions as to what I could do?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    You don't show any control signals. How are you driving the control lines?

    hgmjr
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    As hgmjr has said, signals and a full schematic would be helpful.

    One other thing - the 4016 was declared obsolete 30 years ago. The 4066 is a better alternative.
     
  4. robby991

    Thread Starter Active Member

    Dec 17, 2007
    79
    0
    Ok thank you. I am not sure if we have the 4066 in our lab. I only found the 4016, but I will check.

    I am just pulling the control lines high to vdd and letting the pulse train pass through (about 5k hz). When I use separate ICs for each pulse train the signal is fine. When outputs are connected together there is problems.
     
  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Are you trying to select one of the three pulse trains?

    If so, the current connection will work.

    However, you must fit pull down resistor say a few KΩs on all the control gate pins to 0V so that those control gate(s) not being pulled high to Vdd is pull at 0V level.

    Letting the gate pin float could turns the switch partly on and causes interaction with other pulse trains since you have connected the outputs together.
     
  6. robby991

    Thread Starter Active Member

    Dec 17, 2007
    79
    0
    Seems to be working. Thank you!
     
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