amplification of 1mv analog signal to 1v

Discussion in 'General Electronics Chat' started by theantpbf, Aug 26, 2016.

  1. theantpbf

    Thread Starter New Member

    Aug 26, 2016
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    Hi guys,
    I am currently trying to amplify 1mV analog signal to 1V.
    What is the best way to do that?
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
    819
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    Design an amplifier string with a combined gain of 1000.
     
  3. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
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    Bandwidth of interest?
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
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    What frequency? For most op amps it may be difficult to get a gain of 1,000 at a high frequency.
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
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    Gain-Bandwidth
    The standard LM741 gets less gain as frequency increases. Under ideal designs you might get a gain of 1,000 at a frequency of 1,000 Hz (1 MHz GBW). If your frequency is greater than 1 KHz you need more than one stage.
    To get an overall gain of 1,000 you need two stages of about 32. You might get that gain of 32 at up to 100 KHz.
    So, what is your frequency?
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,540
    1,251
    AC
    DC
    common mode rejection
    source impedance
    input impedance
    output impedance
    load impedance
    anything

    ak
     
  7. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
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    Design 820 b gain of 1000.PNG Design 820 a gain of 1000.PNG
    Crude and unfinished ideas, but just to give you an idea. Battery powered was assumed. Two 9 V batteries.
    Below 1 KHz only one op amp is necessary. Two op amps gets you up to 100 KHz.
    Better op amps may get you better results. Definitely needed for frequencies above 100 KHz. No filtering is shown, not knowing what your frequency is.
     
  8. theantpbf

    Thread Starter New Member

    Aug 26, 2016
    7
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    Bandwidth is 100Hz- 1KHz.
    Little more details on my project.
    I am designing driver for BLDC motor and I am using IC with build in shut of 3 mOhm.
    The motor is small and the current is 0.42A without load up to 20A with max load at voltage 14VDC
     
  9. theantpbf

    Thread Starter New Member

    Aug 26, 2016
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    Thank you hp1729,
    Looks like your ideas are what I am looking for
     
  10. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Note that the bandwidth of the single 741 op amp circuit gives a -3dB rolloff at 1KHz for a gain of 1000, since the op amp has a gain-bandwidth of about 1MHz.
    For less rolloff at 1kHz, you would need a higher gain-bandwidth op amp or the two op amp circuit.
     
  11. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,146
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    Help us out a bit more. What IC are you using?
     
  12. theantpbf

    Thread Starter New Member

    Aug 26, 2016
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    It is STK984-090A-E.
    According to specs, this IC has current sensing resistor with min 2.91 mOhm, typ 3mOhm, and max 3.09 mOhm
     
  13. hp1729

    Well-Known Member

    Nov 23, 2015
    1,954
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    Certainly agreeable on a better op amp (and circuit). Would a single supply op amp be better for him?
     
  14. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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  15. theantpbf

    Thread Starter New Member

    Aug 26, 2016
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    What do you mean by more issues ?
    The current measurement is for speed control and that control does not have to be very precise.
    Also, I can get rotor speed calculating it from current's frequency through windings but that calculation gives me possibility to miss unwanted rotor's slip. I mean that calculation is not enough.
     
  16. panic mode

    Senior Member

    Oct 10, 2011
    1,320
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    that is motor driver... what exactly you wish to accomplish? measure current draw using sense resistor in the IC? this resistor is on high side and you don't want AC coupling.
     
  17. theantpbf

    Thread Starter New Member

    Aug 26, 2016
    7
    0
    I know that is a BLDC driver. I wan to measure the current on the high side and there is no AC coupling.
    Due to high frequency of switching the drawn current is AC not DC. BLDC has AC current trough windings
     
  18. panic mode

    Senior Member

    Oct 10, 2011
    1,320
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    i agree with suggestion in post #14
     
  19. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    There are OP-amp selection issues when the common mode range exceeds the power supply. Standard run of the mill OP-amps won't cut it. The second choice allows the micro to read the values with an EXTRA part.
     
  20. theantpbf

    Thread Starter New Member

    Aug 26, 2016
    7
    0
    I got it now.
    Thank you for clarifying that issues
     
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