Hi again
Today I stumbled on a problem with my Hantek DSO5072p that has the DSO5202p firmware and has the two capacitors removed at the AD converters.
When measuring on a differential DDR memory clock signal i noticed that the channels are not in phase even if i measure from the same pin.
It looks like one channel is filtering the signal little more and at the same a small phase shift can be seen.
The picture below is measured from clk_p and clk_n so they should be inverted without the phase shift. (Unfortunately the picture when measured from same point was not saved)
I opened up the DSO5072p to see the input stage.
The RX1_1, RX1_2, RX1_3, RX1_4 seem to be 499ohm on my device (marking 68A). I have read in the forum that the 200MHz model should have 280ohm 0,1% so I will give that a try for to correct the phase shift.
The following picture shows the input stage on my DSO5072p (Bought 2014)
The differential amplifier seems to have the numbers scratched of. It is probably still a LMH6552 as on the other boards.
Maybe the phase shift could be corrected from the trimmer capacitor on the input. Has anyone got any idea about the trimmer?
I will keep you updated how the resistor change at the differential amplifier affects the signals.