# Magnitude function analog circuit (square root of sum of two squares)

1. ## Magnitude function analog circuit (square root of sum of two squares)

I have output of quadrature mixer and I need it's magnitude for current application. I want to build a circuit that does A = sqrt(I^2+Q^2), and it should also have duty cycle of 10%, so it should be triggered by that function.

Can someone point me to a resource (website, book, journal, etc.) that explains how to build it?

•

2. ## Re: Magnitude function analog circuit (square root of sum of two squares)

Not enough to multiply the I branch with the Q branch signal? The multiplied output's DC level should be rational with the I and Q magnitudes. RSSI operates this way usually.
Tell us more about the application, the operating frequency, and explain this please: "have duty cycle of 10%, so it should be triggered by that function" I don't get it what you mean on.

•

3. ## Re: Magnitude function analog circuit (square root of sum of two squares)

Originally Posted by frankrose
Not enough to multiply the I branch with the Q branch signal? The multiplied output's DC level should be rational with the I and Q magnitudes. RSSI operates this way usually.
Tell us more about the application, the operating frequency, and explain this please: "have duty cycle of 10%, so it should be triggered by that function" I don't get it what you mean on.
By 10% duty cycle I mean that the my I&Q signals are on for 10% of the time. I'll see what happens when I multiply I by Q.

•

4. ## Re: Magnitude function analog circuit (square root of sum of two squares)

In case of doubt, you'll implement the analog function blocks according to the given formula: squarer, sum, square root. In case you use single quadrant multiplier, absolute value will precede the squarer.

--[[ ]]--