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Review of Jim Williams: AN120 1ppm Settling Time Measurement for a Monolithic 18-Bit DAC

Download AN120 1ppm Settling Time Measurement for a Monolithic 18-Bit DAC (2010, Linear Technology, 36 pages, 2.03 MB pdf file)

The title of the application note is an understatement: As Williams explains in a footnote on page 1, he actually developed a settling time measurement technique for 20 bit (1ppm) resolution ! The app note contains a lot of interesting details how this goal was achieved, but the most widely applicable parts are the appendices. Especially interesting are Appendix B (Evaluating Oscilloscope Overdrive Performance p.14-16 ), Appendix G (Breadboarding, Layout and Connection Techniques p.24-29) and Appendix H (How do you know it works, p.30-33). Williams returns to settling time measurements in AN128 2 Nanosecond 0.1 Percent Resolution Settling Time Measurement for Wideband Amplifiers.

Appendix B contains a short discussion of the effects of overdrive on analog and digital scopes (and also on the more exotic sampling scope). This behavior is normally not specfied by the scopes manufacturer, but Williams shows how you can determine how much your scope is affected by this problem. Appendix G discusses some of the neccessary measures regarding the layout and shielding of the circuit that ensure its performance. 5 photos show every detail of the circuit, together with detailed explanations. Appendix H discusses the extraordinary pulse generator that Williams used to verify the performance of his settling time test circuit.

You may also be interested in some other Application Notes by Jim Williams.

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