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MUX506: channel signal glitch influenced by other channel signal

Shuang Feng76
Expert 3310 points
Part Number: MUX506

when used MUX506 transmit signal alternatively, there will be glitch in channel which be influenced by other channel signal.

(different channels are detecting sensors signals.)

you can see the normal signal is well. when there is no signal, the channel will be influenced by other channel signal.

about this could you please give an theory analysis? and is there hardware solving solution? of course, if there is P2P device could solve this problem is better.

hope for your comments.

 

  • 0
    Guru 276530 points

    Crosstalk is specified as no more than −83 dB.

    It's possible that the noise is coupled through the power supply (VDD/GND/VSS), probably due to insufficient decoupling. Please show the schematic and the board layout.

    But those slow edges look as if the signal might be floating. Is that what you mean with "no signal"?

  • 0 in reply to Clemens Ladisch
    TI__Expert 3310 points

    This maybe not crosstalk. it is like the switch open in floating channel, there is a glitch output to end detect system.

    Yes, the glitch in the red circle are appeared in the output when the switch open no signal input channel. this channel input is floating. in this time, there is a glitch in the output. in theory there will be no output. this is the problem point.

    hope for your comments and suggestion.

  • 0 in reply to Shuang Feng76
    Guru 276530 points

    When the input is floating, then the output also is floating. A floating line will easily pick up noise from anywhere, and the mux in the middle does not really change this.

    I suspect that only the 1 MΩ input resistance of the oscilloscope makes the signal float towards GND. If you want the signal to be at GND, add a stronger pull-down resistor.

  • 0 in reply to Clemens Ladisch
    TI__Genius 9132 points

    Hi Shurang,

    I agree with Clemens. The issue is probably due to floating line that should be in a "known" state to avoid any glitches/noise.

    Please let me know if the issue gets resolved when you add the pull down resistor to GND,

    Thanks

    Saminah