Frequency spectrum correction method for the ADC testing

The main issue of high resolution ADC testing in the frequency range from hundreds of KHz to several MHz is the spectral purity of a testing signal. Commercial low distortion generators can operate only up to the frequency of one or two hundreds of KHz; generators operating in higher frequency range have generally the spectral purity worse than the one corresponding to the ADC resolution. Some improvements can be brought by filtering of the testing signal. Most of the LC filters for the frequency range up to several MHz contain coils with ferromagnetic cores. This causes the rise of higher harmonic components. If those components are known or determined by measurement, they can be subtracted from the frequency spectrum measured by the tested ADC. In the ideal case, only a frequency spectrum corresponding to the ADC non-linearity remains. The measurement system designed for frequency spectrum correction and the first results achieved by applying this method are introduced in the paper.