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Altera_Forum's avatar
Altera_Forum
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10 years ago

Generating 400MHz external clock (Cyclone V)

Hello, I'm trying to generate a 400MHz clock signal from my Cyclone V in order to drive the clock input for an external ADC, but I'm getting severe attenuation on the clock signal. Details: ...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
10 years ago

Your scope probably does not have enough bandwidth.

The Fourier Transform of a (perfectly symmetric) square wave has odd harmonics

http://mathworld.wolfram.com/fourierseriessquarewave.html

so your 400MHz square wave has a fundamental at 400MHz, and the first harmonic at 1.2GHz. Hence, your 1GHz bandwidth scope attenuates the harmonics, and makes your square wave look like a sinusoid.

Cheers,

Dave