Multiplexer Characterization for mV amplitude Signals

Discussion in 'The Projects Forum' started by aj pik, Oct 29, 2014.

  1. aj pik

    Thread Starter New Member

    Oct 29, 2014
    3
    0
    I am looking for multiplexer to use for high speed data sampling for low amplitude time varying signals. Unfortunately, there is not a lot of documentation about multiplexers and I have observed behaviors of the few I've tried that were not mentioned on the datasheet.

    How can I model a multiplexer? I understand there is some R_on and Capacitance, how can I begin drawing that?

    Does anyone know of good simulation files for LTSpice (or something) for multiplexers?

    Does anyone know of a very accurate and high speed muxer good for mV analog signals?


    The ones I've tried seem to have a transient response that squashes the signal if it is under 200 mV, but I'm trying to avoid amping it pre-mux.

    Thanks!

    AJ
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,145
    1,791
    The model is a series R and a shunt C.

    You can build a mux out of JFETs. A negative voltage on the gate will turn it off, and GND will let the signals pass through.
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,018
    3,235
    The problem is the switching signal feedthrough from the CMOS transistors gate-channel capacitance. To minimize that you want a multiplexer with low charge injection from switching (usually given in the data sheet). Maxim or Analog Devices, among others, should have such devices. The old 4000 series CMOS muxes, such as the CD4051 have high capacitance so are not suitable. The multiplexer will carry the millivolt signal accurately after the transient has settled so you need some settling time before you measure the signal level. Settling time can also be shorted by having a low signal input impedance on the multiplexer input.

    Edit: Here's a paper that may help.
     
  4. DickCappels

    Moderator

    Aug 21, 2008
    2,656
    632
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