I recently got an Agilent 5488A Scope, it has 1134A probes and I'm using E2678A differential heads.
The scope is goig to be used for work on computor memory. To verify everything was working okay I wired up CLK / CLK# on a standard DDR2 UDIMM module. When I look at both signals on seperate probes everything looks fine but when I hook both up to the one differential head it still looks like I'm looking at just one of the signals (i.e. signal is still fairly jagged, duty cycle etc isn't as even as it should).
I've calibrated the probes and checked the differential box etc.
I feel I may be doing something goofy here but I can't work out what it is.
Hope someone can help.
Thanks
The scope is goig to be used for work on computor memory. To verify everything was working okay I wired up CLK / CLK# on a standard DDR2 UDIMM module. When I look at both signals on seperate probes everything looks fine but when I hook both up to the one differential head it still looks like I'm looking at just one of the signals (i.e. signal is still fairly jagged, duty cycle etc isn't as even as it should).
I've calibrated the probes and checked the differential box etc.
I feel I may be doing something goofy here but I can't work out what it is.
Hope someone can help.
Thanks
It sounds like you are having signal integritiy issue like maybe probing mid bus? Below are a few suggestions.
JDEC spec is defined at the DRAM *****. You must probe as close as possible to the DRAM or you may see phase shift between clock and data.
Clock, DQ, and DQS all phase aligned that is why it is important to probe on the DRAM *****. The further from the DRAM ***** you connect the probe, the greater the possibility of phase shift and measurement errors.
Make sure you connect the probe ground to the closest ground point on the PC board. Ideally, the ground point should be right next to the pin you are measuring. The longer the ground path, the greater you will not get correct measurements or signal display.
DDR bus is parallel, but the bus speeds are faster than most serial busses. Because the bus is parallel, measurements are also single ended. You can use single ended probes for your measurements, but differential probes will give you better ground and better measurements results.
You might also try the resources at this web site.
http://www.home.agilent.com/agilent/app ... geMode=OVW
I will ask around to see if there are any additional suggestions.