Effective Number of Bits (ENOB): The Best Digitizer Performance Metric

While the nominal vertical resolution of a high-speed waveform digitizer (specified in bits) is often promoted, its true performance is provided by its measured Dynamic Parameters and in particular by its Effective Number of Bits (ENOB). This article describes the measurement of the Dynamic Parameters and presents measurements for a leading-edge GaGe 12-bit Digitizer.

A widely used digitizer-like device, the Digital Storage Oscilloscope (DSO), is optimized for the visualization of unknown signals. The relatively low 8-bit vertical resolution of most DSOs is sufficient for signal visualization and is offered at the highest sampling rates (~200 Giga Samples/second). Furthermore, high-end DSOs are often optimized for the determination of signal edge positions in the time domain, such as in eye-diagram measurements. Accordingly, product marketing typically promotes DSO’s high input bandwidth and vertical performance parameters are not emphasized.