Video Design Idea: Measure nanoamps to ensure accurate computer clocks
In this EDN Video Design Idea, Jim Williams, staff scientist with Linear Technology, explains why PC clocks are invariably wrong, and how engineers can surmount the extreme measurement challenge involved in solving the problem.
By Staff -- EDN, 5/10/2007
Bonnie Baker, senior applications engineer at Texas Instruments and regular EDN columnist, demonstrates a simple way to add DAC functionality to a microcontroller-based system using only an op amp and two passive components.; Bonnie Baker; DAC; EDN.com; analog design; op amp; video design idea; Mark Thoren, mixed-signal application engineering manager with Linear Technology, demonstrates an amplifier-based circuit design for a relatively inexpensive precision voltage source.; Mark Thoren; amplifier-based circuit design; linear technology; mixed-signal application; precision voltage source; Jim Williams, staff scientist with Linear Technology, explains why PC clocks are invariably wrong, and how engineers can surmount the extreme measurement challenge involved in solving the problem.; cell phones; computer clocks; jim williams; linear technology; nanoamps; quartz crystals; video design idea; EDN Tech Clips deliver technical depth and tutorial design information for engineers involved in analog circuit design, power management, embedded-system design, board-level design, signal integrity, and more. http://link.brightcove.com/services/link/bcpid1125855242http://www.brightcove.com/channel.jsp?channel=959007201
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The extremely low-power quartz crystals that are prevalent in products from cell phones to PCs today work with currents that max out at 1 µA. With such a small full-scale current range, a seemingly tiny error in the current a circuit sends through the crystal can result in terribly inaccurate clocks. Designers can address that problem by accurately measuring the current through a crystal and tuning their circuit design for precision. But as Jim Williams explains, measuring current in the sub-µA range is difficult, and the measuring circuit can induce no more than 1 pF of capacitance.
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