How to square a signal?

Hi,
are there any ideas how to square / squareroot a signal in the analog world? This should not be done with a DSP!

Ideally, I'd like to build up a circuit with the following transfer function: OUTPUT=√(x²+y²)
-> Square signal x, square signal y, sum them up, squareroot the result

I've already found multipliers such as the Analog Devices AD835, but they don't seem to be able to square a signal.

The reason is, I'm having the outputs of an IQ-demodulator which have to be squared to get rid of phase/frequency differences.

As I can understand you need to extract the amplitude of the modulation.

you can find useful to use an approximation to the amplitude extraction that do not use square and square root.

Yes, I need to get the amplitude of the signal.

There is no other way round though for demodulating an AM-signal which is mixed down to baseband/very low intermediate frequency (at least I don't know any other way). In an IQ-demodulator both outputs are 90° phase shifted, so with squaring both outputs (sin²+cos²=1) I get a constant amplitude.

So I have to square the signal somehow...but don't know how to do this the best/easiest way.

arefeidi,
You can use an analog multiplier to perform the squaring function. Just connect the X, Y inputs together. To perform the square root function, connect the multiplier as a squarer, as described in the previous sentence. Then connect the squarer in the feedback loop of an op-amp. Connect the squarer from the output of the op-amp through a feedback resistor (R) to the inverting input. Connect the input to the inverting input of the op-amp through another resistor equal in value to the feedback resistor. The input must be a negative voltage. The output will now be the negative of the square square root of the input magnitude. You must be careful not to provide a positive input voltage, otherwise, the op-amp will always be saturated at its maximum negative value.
Regards,
Kral

Connect X and Y, that's it...I was thinking to complicated again, thanks!
Also thanks a lot for the idea on how to implement the square root function, I'm sure this wil help me a lot.

I remember some books talking about using
logarithmic amplifiers to multiply two signals,
but I do not have the references with me right
now.

FET can act as squarer ..based on this it used in modulation technique

at first y can use the AD8313 to get the amplitude and then use a MCU to do this function, this is more easy

Micro or some timeing circuit, such as 555 can be used.