Determination of coherence errors in ADC spectral domain testing

Coherence of the input and clock frequencies input to an analog-to-digital converter (ADC) during the spectral domain based effective number of bits (ENOB) test is desirable in order to achieve reproducible results without resorting to windowing functions. Impact of these errors on the ENOB test of an ADC is first discussed. A simple model of an ADC used to test the effect of coherence is given. Then this paper presents a method to detect and measure these coherence errors. The ADC model is used to demonstrate this method. Experimental results applied to a 10-bit 40 MSPS converter with a 10 MHz input sinewave are also presented.