DNL ADC testing by the exponential shaped voltage

Testing of ADC differential nonlinearity DNL(k) by histogram method requires a signal generator with extremely low distortion and high stability of parameters. A new type of stimulus signal has been proposed, which achieves this requirement. The studied testing signal has exponential form and is generated by discharging of a capacitor across a known resistance. Also, the generating circuit could be ideally connected at the input of the ADC under test without any interfering coupling with other instruments. The acquired digital samples from the output of the ADC under test allow to determine the best fitted exponential signal by a three parameter method. The histogram from registered samples and that for the best fitted exponential shape allows to determine the differential nonlinearity DNL(k) for any code level k. In order to test each code level with a similar number of samples the exponential shape was split into subparts. The acquired DNL(k) for each subrange are fan-folded over the whole ADC input range. The proposed method has been experimentally verified for the ADC embedded on microcontroller ADuC812 where the testing results were compared by standardized methods. The achieved results are in agreement.