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Sampling above 50MHz

PostPosted: Thu Dec 17, 2015 12:06 pm
by rosin232
So I tried to take a trace of 25Mhz clock from SPI flash and if you sample at 50Mhz it works OK I compared it with Saleae logic analyzer if you go 100MHz and above results start to changes and it shows weird period 20MHz instead of 25MHz at 100/200 and 400MHz sampling results are different for the same signal. Looks like firmware update is needed? Yes I'm using latest v0.95 DSView. See attached samples.

Re: Sampling above 50MHz

PostPosted: Fri Jan 08, 2016 12:52 am
by Andy
Hi rosin232,

Obviously, The clock you measured is not a 25M signal, the real frequency is about 19M.
With higher sample rate, you will get more detail of your signal.
For example, with 400MHz sample rate, per 2.5ns a point will be sampled.
with 50MHz sample rate, per 20ns a point will be sampled.

50MHz.png
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