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I have to study biomedical electronic, but there is a problem. I searched but could not find things I want.

How can I design squaring circuit with op-amp, if input is a 50 mV and I have to get output value = X^2. = 2500 mV for example?

Mehmet
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    As always, AN-31. – Ignacio Vazquez-Abrams Oct 12 '16 at 07:54
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    \$50^2 \neq 250 \$ ;) You need a multiplier circuit. This paper will help you: http://nopr.niscair.res.in/bitstream/123456789/6896/1/IJPAP%2048(1)%2067-70.pdf Also, as @IgnacioVazquez-Abrams stated, "Opamp Circuit Collection" will help you as well: http://www.ti.com/lit/an/snla140b/snla140b.pdf – Rohat Kılıç Oct 12 '16 at 07:56
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    @Mehmet Do you mean a circuit that converts a sine wave to a square wave? Is your input going from 0V to 50mV, or is it -25mV to +25mV? – Steve G Oct 12 '16 at 07:59
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    Your question is unclear, are you looking for a circuit that takes \$ V_{in}\$ as input and produces \$ \frac{V_{in}^2}{10}\$ as output? – Warren Hill Oct 12 '16 at 11:13
  • why only 250mV square wave. what frequency , source impedance, and Vmin input will determine gain and hysteresis required with full scale clipping and R divider to reduce to 250mV.. details please. – Tony Stewart EE75 Oct 12 '16 at 11:18
  • @Rohat Kılıç: nobody claimed that \$50^2=250\$. By saying that the squaring circuit should output 250mV for an input of 50mV the OP just defined the otherwise arbitrary nomalization constant to be 10mV because \$(\frac{50mv}{10mV})^2=\frac{250mV}{10mV}\$. – Curd Oct 12 '16 at 15:44
  • @SteveG ı mean that think about an input has a X value and output have to give me X^2 . – Mehmet Oct 12 '16 at 17:56
  • @TonyStewart.EEsince'75 ı study on biomedical signal therefore signals have small value and ı have to take a signal that input value is X and output value is X^2. Other components are not important for now – Mehmet Oct 12 '16 at 18:04
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    _Why_ do you need to square the signal? – Bruce Abbott Oct 12 '16 at 18:40
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    @Mehmet: Wait, why do you need to square it then? It sounds like all you're after is an amplifier. Squaring the result is a nonlinearity... what's the purpose of squaring it rather than linear gain? – Synchrondyne Oct 12 '16 at 19:07
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    @BruceAbbott, i'll bet it's because he wants a power signal. if the OP wants r.m.s., he'll need to square root also. it will seem silly if this squared biomed signal gets sampled and inputted into an embedded processor or DSP, in which the squaring can be done with a single instruction. – robert bristow-johnson Oct 12 '16 at 19:39
  • @PeterK This is an experimental circut and professor wanted from me that I answer it but ı could not – Mehmet Oct 12 '16 at 20:00

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Because of the difficulty in calibration of a true Analog multiplier, it is best to consider the use of a suitable chip with factory laser trimmed offset and gain IC, such as ;

www.analog.com/media/en/technical-documentation/data-sheets/AD534.pdf

enter image description here

There is a wide selection range and many suppliers, AD835 AD633 AD734 AD834 AD538 AD539 AD632 AD534 AD532

http://www.analog.com/en/parametricsearch/11106?doc=AD534.pdf&p0=1&lsrc=pst&doc=AD534.pdf&p0=1&lsrc=pst#/ps5=select%20all

Lowest cost is the AD633 < $5 (1k) enter image description here

Tony Stewart EE75
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  • If you only need 1, there is an EVAL board http://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/eval-ad633.html#eb-buy – Tony Stewart EE75 Oct 12 '16 at 18:28