Moving an analog signal to a shaky ground

Discussion in 'The Projects Forum' started by kender, Sep 24, 2009.

  1. kender

    Thread Starter Senior Member

    Jan 17, 2007
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    Colleagues,

    Could you provide some ideas, insights or typical solutions for the following problem. I have 2 ground “domains” in my system. They are galvanically connected, but due to currents and resistances in my system, a potential up to 150mV can appear between the grounds. I would like to bring an analog DC signal which is generated on one ground to the other ground. E.g. 1V with respect to GND1 it will always be 1V with respect to GND2, provided that GND1 and GND2 are no further than 150mV apart.

    At the moment I can see 2 ways of doing this: a differential amplifier or a current mirror. What could the other options be? How is it typically done?

    Cheers,
    - Nick
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    Is the analog signal going to be fed in an IC?
     
  3. kender

    Thread Starter Senior Member

    Jan 17, 2007
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    Yes, it will be fed into an OpAmp (which is a part of a constant-current driver for an LED).
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    Disconnect the ground of the op amp from GND2 and connect it to GND1.
     
  5. kender

    Thread Starter Senior Member

    Jan 17, 2007
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    If it were that easy, I would not have started this thread. ;) The OpAmp has to take other signals which are referenced to GND2 (they "live on" GND2 entirely). Later today I'll post a schematic snippet.
     
  6. retireme

    New Member

    Aug 28, 2009
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    HI, I had a similar problem with a printed circuit for a distribution amplifier that had a difference in ground voltage between ground pathes. I cut a strip of tin from a tin can ( washed it well of course) that contained peaches. I formed the tin strip to match the ground pathes, tinned it and soldered it to the board so the 2 grounds were connected together. This made both grounds to have the same voltage . I sometimes, on some boards I had to connect a large gauge wire from the tin strip to the main ground at the power supply to get 0 volts . I hope this can help you. Best Regards :)
     
  7. mik3

    Senior Member

    Feb 4, 2008
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    You can provide a separate ground wire (track) for those devices which require high current and use another one to reference your signals.
     
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    +1. That's how it is done. You need a clean analog ground for analog circuitry, a power ground for high current returns, and if necessary: aswitching ground for the returns of switching transistors or switch current from filter caps. It's all about ground management.
     
  9. kender

    Thread Starter Senior Member

    Jan 17, 2007
    263
    0
    Basically, you're proposing to decrease the resistance of the ground paths, which will result in a smaller and acceptable I*R drop. I'll use this approach as much as I can. But given the constraints, I'm not sure that this approach alone will solve the problem.

    There already are separate ground tracks for power and signals: GND1 and GND2 (see above). The problem affects the chips that need have both types of analog signals: the ones referenced to GND1 and the ones referenced to GND2. Hope this helps to understand the problem.
     
    Last edited: Sep 24, 2009
  10. mik3

    Senior Member

    Feb 4, 2008
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    A circuit diagram will give much more information.
     
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