Need Pulse-Triggered Switch

Discussion in 'General Electronics Chat' started by johnyradio, Nov 9, 2012.

  1. johnyradio

    Thread Starter Member

    Oct 26, 2012
    39
    1
    hello

    i am seeking a pulse-triggered switch. It should change states on a pulse, but not require continuous high-state to stay switched.

    i am trying to route an analog voltage to two different outputs.

    a trigger pulse to one pin should route the input to output A.

    then, a trigger pulse to a different pin should route the input to output B.

    as always, seeking simplest possible approach.

    there should be no leakage in open position, and no voltage drop or gain in closed position (or easy to compensate).

    again, should not require continuous high-state on trigger pins to maintain switch state.

    should be able to switch at least 1 MHz.

    thanks!
     
  2. timescope

    Member

    Dec 14, 2011
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  3. johnyradio

    Thread Starter Member

    Oct 26, 2012
    39
    1
    Thanks, I considered that, but its Operate time is 2 ms and its
    Minimum operate pulse is 6 ms, which I believe limits its switch freq to about 100 Hz. I need 1 MHz.

    I think I could use a flip flop to turn a pulse into a steady high, and use that high to enable a standard solid state switch. Would that work?

    Cheers?
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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  5. johnyradio

    Thread Starter Member

    Oct 26, 2012
    39
    1
    Nice!

    Can anyone recommend a logic controlled analog switch which provides essentially 100% throughput when closed and 0% when open?

    Talking low-current application.
     
  6. ScottWang

    Moderator

    Aug 23, 2012
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  7. johnyradio

    Thread Starter Member

    Oct 26, 2012
    39
    1
    Fantastic.

    Thanks!
     
  8. timescope

    Member

    Dec 14, 2011
    298
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    The 4051 and 4066 CMOS analog switches have leakage currents Is (off) in the off state and ON resistance Ron (max) specified in the datasheets.

    Timescope
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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    The messages of CD4051 and CD4066 on the 1st page.

    CD4051 : High "OFF'' resistance: channel leakage of ±10 pA
    (typ.) at VDD-VEE=10V

    CD4066 has Extremely Low Off-State Switch Leakage Resulting in
    Very Low Offset Current and High Effective Off-State
    Resistance: 10pA Typ. at VDD - VSS = 10V, TA = +25℃
     
  10. timescope

    Member

    Dec 14, 2011
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    These are typical values. The datasheet section " DC electrical characteristics " shows a maximum leakage of +/- 200nA @ 25 deg C for CD4051. Worst case values are usually used in good designs.
    We should also consider the effects of clock feedthrough, which is some of the control signal appearing at the output, because the switch is required to change state at 1 MHz.

    Timescope
     
    Last edited: Nov 10, 2012
  11. ScottWang

    Moderator

    Aug 23, 2012
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    767
    That is very tiny for the most used which not request the low leakage current, if the system request a very low leakage, then at that kind of situation we can't use this IC.

    The CD4051 used very often in the industrial, so if request very low leakage current, maybe it needs a relay to do it.
     
    timescope likes this.
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