I have a problem using an A/D converter:
I am connecting a 10-bit A/D input to a voltage from a calibrator and doing a histogram over 10,000 samples. The results I get is two separate lobes, each one is ~4.5K samples high. The lobes are 2 to 3 counts far from each other and for unknown reason the counts in between them are around 200 to 500 samples high.
What can be wrong in the implementation to cause this phenomenon ? Can anybody help? Many thanks, Shlomi
Shlomi wrote in sci.electronics.design:
That's consistent with a DC voltage overlaid with a small square wave.
Anno
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Effects like you are seeing can have many causes.
Take a look at the diff. nonlinearity spec. for the ADC. This would have to be a bad one for it to be this.
If the output is parallel, is the ADC's output driving the previous value as you convert the next? The digital sides currents can be making offsets.
Plot the data and look at it, there may simply be a step in it or a square wave or the like.
If it has an external reference, is the reference to the ADC good and clean?
If the ADC has an external clock, does this clock come from a circuit that puts systematic jitter on it? A divider chip that has bits below the one used as the clock can do this.
Are you reading the ADC before it is really finished?
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Are the lower bits of the output being transposed somehow?
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