Level-Crossing ADC Performance Evaluation Toward Ultrasound Application

A performance evaluation of a level-crossing analog-to-digital converter (ADC) is presented. It is shown that its signal-to-noise ratio (SNR) does not depend on the input-signal amplitude, which results in an almost-flat SNR for amplitudes that fall into the Nyquist criteria for irregular sampling. The influence of the reconstruction procedure on SNR is discussed, and possible limitations due to the comparator and clock on the performance of the ADC are analyzed. This analysis allows for specification of comparator and clock parameters such that they do not limit the ADC performance yet are not overestimated. In conclusion, a previously known level-crossing ADC design procedure is extended. A level-crossing ADC design example is given for intended use in an ultrasound application with a frequency band from 1 to 10 MHz. MATLAB and Cadence simulations, which utilize the data obtained from a real comparator and clock, are presented, and the performance of such a level-crossing ADC is compared with a conventional ADC.