8 bit Pipeline ADC measurement problem

[guanglei]

Hi, I am testing a 8 bit pipeline ADC, each stage is 1.5 bit, input a ramp signal, I am attaching the ADC output, there are some jumping code, like from 0 to 64, 64 to 96, 96 to 112, 160 to 192, 192 to 224 and 224 to 256, the ramp signal is slow enough so it sweep less than 1LSB, what's possible problem with this ADC, is there something wrong with some specific MDAC?thanks for help!

 

[fogandflower]

seems the last 4 LSB always at 0000, only able to see the first MSB changing.