Signal multiplier

Discussion in 'The Projects Forum' started by Closedloop, Jun 27, 2014.

  1. Closedloop

    Thread Starter New Member

    Jun 27, 2014
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    Hello guys, I'm working on a closed loop control. I need to take a signal and multiply it by itself as many times as I want (exponentiation) using an analog circuit.
    Do you know if anything like this exists?
    Thank you very much for your support
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    wouldnt that be called an amplifier?
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,145
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    Do you mean you want to increase a DC voltage? That's called a variable gain amplifier. Depending on the specs you need, it could be as simple as a basic op-amp circuit. Note that your power supply has to provide the voltage you need at the output.

    Oh, I missed the exponentiation part.
     
  4. Closedloop

    Thread Starter New Member

    Jun 27, 2014
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    No guys I need more than a simple amplifier. I don't want to multiply the signal by a constant value but I want to multiply it by itself.
    I'm sorry if the explanation wasn't clear
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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  6. Closedloop

    Thread Starter New Member

    Jun 27, 2014
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    Thank you for your answer alfacliff, i can probably use it for my purpose. Anyway what I was interested in knowing is if I could do something like this.

    Take as input the signal X and generate as output X^33
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,028
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    You do realize that with such a huge exponentiation factor you will rapidly reach near zero volts or saturate the output for any voltage that isn't very near 1V(?). Why on earth do you want such a huge factor? :confused:
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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  9. Brownout

    Well-Known Member

    Jan 10, 2012
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    log-1(logx*A) = x^A, right? So you need log/anti-log and an amplifier.
     
    Last edited: Jun 27, 2014
  10. Closedloop

    Thread Starter New Member

    Jun 27, 2014
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    @crutschow I need an algoritm that amplifies alot values far from 0 and less values near 0. Analysing my signal I realized that I need high factors to do that. Probably there are other ways to do it like e^(n*x) where x is my signal and n is a constant anyway i want to compare them.

    @DickCappels I need to do a very fast closed loop control (microseconds), so A to D is not the best choice in my case

    @Brownout that's very clever, exactly what I was looking for

    Thank you all for your support guys
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    You need an anti-log circuit:

    [​IMG]
     
  12. crutschow

    Expert

    Mar 14, 2008
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    3,236
    Below is a simulation of MrChips' circuit. Note that the gain change is logarithmic with a large change is gain (bottom plot has a logarithmic scale). It takes about .34V In to give 10mV Out but .65V In gives 7.9V Out. I added an inverter stage so both input and output are positive.

    Note that this only works for input positive signals.

    If you want a little more gain at lower input signals you could add a resistor in parallel with the diode.

    Is that sort of what you are thinking of?

    Antilog.gif
     
  13. Brownout

    Well-Known Member

    Jan 10, 2012
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    I think we decided we needed a chain: log amplifier - constant gain amplifier - anti-log amplifier to acheive the OP's required function.

    However, be aware that these simple log/anti-log amps suffer sever temperature instability. Better to use intgegrated solutions, but they appear to be very expensive.
     
  14. Closedloop

    Thread Starter New Member

    Jun 27, 2014
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    Exactly what I needed crutschow.
    I'll build a test circuit and I will let you know the results.
    Thank you everyone
     
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