how to use instrumentation amplifier AD620?

Discussion in 'Analog & Mixed-Signal Design' started by ahmedzaidan, Jul 28, 2017.

  1. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    Hi

    i need to amplify a signal from (0-5mv) using AD620 to (0-3V)?
    how can i determine the gain and the reference voltage ?

    thanks in advanced :)
     
  2. bertus

    Administrator

    Apr 5, 2008
    18,220
    3,480
    Hello,

    Did you read the datasheet?
    There is a equation for the gain:

    AD620_gain.png

    Bertus
     
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  3. ericgibbs

    Moderator

    Jan 29, 2010
    5,145
    967
    hi,
    The AD620 datasheet gives all the information.
    E
    A002.gif
     
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  4. ElectroHydraulicEng

    New Member

    Mar 31, 2017
    2
    1
    You need a gain of 600. On the datasheet gain is given by (on page 3):

    G = 1+ (49.4 kohms/Rg)

    Rg = 82.5 ohms
     
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  5. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    thanks a lot guys :)
    and what is the purpose of Vref?
     
  6. crutschow

    Expert

    Mar 14, 2008
    19,349
    5,390
    Vref is an input that determines the output voltage for 0V differential in.
    Normally it is tied to circuit common.
     
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  7. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    thanks a lot ^^
    i have tried RG=82.5,V+=5,V-=0,ref=0, input=1mv
    output=4.57 V ?!
    any thing wrong?
     
  8. bertus

    Administrator

    Apr 5, 2008
    18,220
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    Hello,

    An instrument amplifier usualy needs a dual powersupply.
    V+ = +5 Volts, V- = - 5 Volts, Vref = 0 Volts.

    Bertus
     
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  9. crutschow

    Expert

    Mar 14, 2008
    19,349
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    Yup.
    What are the power supply voltages?
    You need a dual supply for that device.
     
  10. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    so it is impossible to use single power supply !!o_O

    is there other instrumentation amplifiers work with single power supply ?

    i have tried v+=5,V-=-5 ,Vref=0.

    it worked fine.. :)

    i need to use microcontroller to read the the output of ad620 .
    should i need to add other elements?or connect it directly?
     
  11. crutschow

    Expert

    Mar 14, 2008
    19,349
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    Why do you need an instrumentation amp?
    Can you use a standard op amp?
     
  12. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    can i use standard op amp with load cell ?
     
  13. crutschow

    Expert

    Mar 14, 2008
    19,349
    5,390
    Is the load cell in a bridge?
    Post your circuit schematic.
     
    Last edited: Jul 28, 2017
  14. ericgibbs

    Moderator

    Jan 29, 2010
    5,145
    967
    hi a,
    The AD623 will work with a single supply voltage.
    We need to see your circuit diagram.
    E
     
  15. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
  16. ericgibbs

    Moderator

    Jan 29, 2010
    5,145
    967
    hi a,
    That is a half bridge, using passive resistors to make up the other half bridge into a full bridge, it is often configured in that way.

    Do you have a AD623 or any regular OPA's that you could use for the amplifier.?

    E
     
  17. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
     
  18. ericgibbs

    Moderator

    Jan 29, 2010
    5,145
    967
    hi a,
    This is a draft circuit for the AD620, uses +/-5V supply to give 0v thru 3V out.
    Have used 350 Ohms for the simulation.
    E
     
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  19. ericgibbs

    Moderator

    Jan 29, 2010
    5,145
    967
    hi,
    If you have only +V supply available, there is this option, using LM324 after the AD620.
    E
     
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  20. ahmedzaidan

    Thread Starter Member

    Jul 22, 2017
    39
    2
    Hi ericgibbs,
    thanks for your appreciated effort :)

    can i build a dual power supply without using transformer and rectifier circuit ?

    with single power supply it would be better to use ad623 instead of ad620+1m324?

    ^_^
     
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