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

 

wouldnt that be called an amplifier?

 

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.

 

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

 

here is one of what a search on "exponential amplifier" came up with.
http://www.cirvirlab.com/index.php/tutorials/80-op-amp-exponential-amplifier.html
there is a lot more too.
here is another.
http://www.cirvirlab.com/index.php/tutorials/80-op-amp-exponential-amplifier.html

 

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

 

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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

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?

 

You are probably looking for an analog multiplier such as:
http://www.analog.com/en/special-li...ltipliersdividers/ad633/products/product.html

Or you may want to read about pulse height-width calculators in this thread:
http://forum.allaboutcircuits.com/showthread.php?t=96068

Consistent with Crutschow's caution, errors accumulate rapidly with multiple analog multiplications. You might find a more satisfying result by using an A-to-D converter followed my a microcontroller to do the math.

 

log-1(logx*A) = x^A, right? So you need log/anti-log and an amplifier.

 

@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

 

You need an anti-log circuit:

 

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?

 

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.

 

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