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Analog switch configuration?

Discussion in 'Electronic Design' started by MRW, Oct 27, 2006.

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  1. MRW

    MRW Guest

    Good day, group!

    My friend has this rough drawing of two analog switch configuration:
    http://img175.imageshack.us/img175/9612/analogswitchesbf9.jpg

    I say that the two SPST configuration would be better suited since it
    would provide better isolation than the SPDT configuration. She says
    otherwise. Am I wrong?

    I also told her that another switch would be required at the output of
    DeviceA so its output will be isolated from the other signal path. She
    thinks it's okay. Is there truth to her claim?

    Thanks!
     
  2. MooseFET

    MooseFET Guest

    It depends on the details of the switches. If you use to SPST switches
    in two packages, your are likely to get better isolation.

    This depends on what exactly DeviceA is. The switch on the output side
    may be all that is needed in some cases.
     
  3. MRW

    MRW Guest

    Thanks, MooseFET!

    I was assuming that DeviceA was just an opamp configuration. However,
    if it is an opamp with some kind of feedback configuration, then the
    signal from the other path would be fedback, right? I think she needs
    some sort of opamp with a shutdown feature or something. That way it
    can be disabled when the other signal path is used.



    This depends on what exactly DeviceA is. The switch on the output side
     
  4. TuT

    TuT Guest

    Since the circuit connects the two switches together, isolation is going to
    be a function of the switches' OFF resistance, rather than crosstalk between
    the two switches, so there's nothing to choose between the two
    configurations.
    No, you're right, you need to disconnect the output of device A when
    connecting 'Signal in' to Signal out', otherwise you will end up with two
    outputs trying to drive one another. (I'm assuming that 'Signal in' is low
    impedance and comes from some type of amplifier and that Device A is itself
    some form of amplifier.

    A simpler arrangement would be to connect 'Signal in' permanently to the
    input of Device A and use the switch, (either arrangement shown in the
    link), to select between the signals on Device A's input and output.
     
  5. jasen

    jasen Guest

    the puropse of these switches is unclear,
    both look equally bad.
    you may need to disconnect the output of "device a".

    Bye.
    Jasen
     
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