The white paper “ENOB: The Best Digitizer Performance Metric” by Andrew Dawson from Vitrek emphasizes the importance of Effective Number of Bits (ENOB) as a key performance metric for high-speed digitizers. Unlike Digital Storage Oscilloscopes (DSOs), which are optimized for visualizing unknown signals, digitizers are designed for high-fidelity signal acquisition and analysis of small changes in familiar signals. The paper explains that while nominal vertical resolution (in bits) is often highlighted, the true performance of a digitizer is better represented by its Dynamic Parameters, particularly ENOB, which accounts for signal distortion and noise. The paper also discusses the distinction between absolute and relative accuracy, and how factors like random noise, signal distortion, and clocking imperfections can affect signal fidelity.
The paper further details the methods for measuring digitizer performance, including time-domain and frequency-domain techniques. It highlights that ENOB combines both noise and distortion into a single metric, making it a comprehensive indicator of performance. The paper presents measurements from a 12-bit GaGe digitizer, showing how design choices impact performance at different frequencies. For instance, the digitizer achieves excellent performance at near 200 MHz but has slightly compromised performance at 10 MHz. The conclusion underscores the importance of considering both ENOB and frequency response when selecting a digitizer, ensuring it meets the specific signal frequency requirements of the application.
