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AD9255 evaluation board output jumps (or missing codes?)

Question asked by GregB-Portland on Jul 22, 2014
Latest reply on Jul 26, 2014 by GregB-Portland

I have an AD9255/105 (running with a 100 MHz onboard clock) evaluation board with the HSC-ADC-EVALC board that I am using to capture exponential decays, which have low frequency components. Since the standard 9255 evaluation board is designed for MHz frequencies, I have modified the optional input path (which has a AD5562 amplifier) to take a DC Coupled, single-ended differential input per the circuit in Figure 36 of the AD5562 datasheet (without the AC coupling capacitor). The path between the AD5562 and the AD9255 I modified per Table 10 and figure 69 of the AD9255 datasheet, again without the AC coupling capacitors.I do get a response at lower frequencies, but I am seeing discrete jumps in the output of the AD, as seen on the VisualAnalog software. I have attached a screenshot of the VisualAnalog output screen showing a typical signal. I also see the same effect in sine wave inputs. If I turn on dithering, it masks the effect somewhat, but it is still visible (also attached).


I would appreciate any help.




ExponentialDecay-No Dithering-22July2014.PNG

ExponentialDecay-With Dithering-22July2014.PNG