I'm examining the uniformity of the distribution of an ADC's binary digital output code when it digitizes a triangle wave that spans its input range. This DNL histrogram graph is done by digitizing many cycles of a triangle wave. NI's references to DNL mention normalizing the histrogram. A graph of the raw histrogram shows periodic spikes in the distribution. A PCI-MIO-16E-4 has high spikes every 16 binary code channels. Most are followed by a negative spike, perhaps indicating that the particular adc bit that should be changing state is instead changing on a lower voltage than it should be. Data acquired at 10 kHz on a 27 Hz trianle wave. Similar results at other acquisition and waveform rates. Spikes also observed on two NI6070E cards (one ISA and one PCI). The 6070 results spiked high every 128 channels and low every 64 channels. Spikes observed digitizing the triangle wave as wellas a random noise source.
Is this a typical characteristic representing DNL but now observed in DNL results due to their being presented in some normalized fashion ? Are there other adc's that do not exhibit this ?
