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measure ddr clock seem strange
noisepic , 01-02-2018, 02:01 AM
When measuring clockp and clockn of DDR3 I expect, clock like this. But measuring clockp and clockn has vary pulse width, including long pulse and short pulse, my board still work fine. I don't know what's wrong here?
robertferanec , 01-02-2018, 11:45 AM
Do you have a special oscilloscope to measure memory clock? You may need special probes and an expensive oscilloscope - what is your DDR3 speed / clock and what kind of oscilloscope and probes you have?
noisepic , 01-02-2018, 09:24 PM
I found myself that I can not evaluate ddr just by oscilloscope, the tektronix system up to 200K$, the probe only has 17K$. That's the reason why I see strange in clk waveform. Suppose that 400MHz DDR clock it mean 2.5ns in period, 1.25ns in pulse width. And we need atleast 125ps rising/falling time oscilloscope (BW>8GHz). So it seem measure DDR3 signal by low performance oscilloscope like a stupid story!
robertferanec , 01-03-2018, 08:19 AM
Do not worry ... we all went through that 
When you mentioned, that memory clock "has vary pulse", I have got immediately suspicious, that there is no enough samples per clock cycle to measure the clock signal properly. That is why I asked about your scope.
When you mentioned, that memory clock "has vary pulse", I have got immediately suspicious, that there is no enough samples per clock cycle to measure the clock signal properly. That is why I asked about your scope.
Luca , 01-03-2018, 01:45 PM
@noisepic do you have a spectrum analyzer? If yes with which setup can you run?
It's still possible to "see" the clock signal, but in frequency domain instead time.
It's still possible to "see" the clock signal, but in frequency domain instead time.
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