W. Stephen Woodward, independent consultant, holds a BS (with honors) in engineering from Caltech, Pasadena, Calif., and an MS in computer science from the University of North Carolina, Chapel Hill. Email address: eecon@email.unc.edu
70 results found for W. Stephen Woodward, displaying items 1 - 20
July 23, 2009[Ideas For Design] Sample 64 Temperature Points For Pennies Per Channel With Multiplexed Delta VBE Thermometry
Delta VBE ( VBE)-based thermometry is based on the “PTAT VBE effect,” which says that for an ideal transistor, the VBE corresponding to changes in collector current is exactly proportional to absolute temperature. Cheap small-signal transistors conform closely enough to the ideal model that VBE circuits can implement accurate and cost-effective thermometers needing no calibration. An earlier Idea for Design...
June 25, 2009[Ideas For Design] Triple-Current-Modulation Delta VBE Thermometry Cancels Ohmic Error Sources
Delta VBE-based ( VBE) thermometry1,2,3,4 is based on this classic bipolar junction I/V/T relationship: For an ideal transistor, the VBE corresponding to ratiometric change in collector current (I2 / I1) is exactly proportional to absolute temperature: VBE = 198.4 µV * °K * LOG10(I2 / I1). Because cheap, common, and robust small-signal transistors conform closely to the ideal model, circuits that exploit the “PTAT (Proportional...
February 26, 2009[Ideas For Design] Isolated Receiver/Converter Uses Multichannel Opto-Isolator
The accurate transmission of analog signals over long distances in noisy industrial environments is a difficult design problem. One of the oldest solutions isolated current loops is still one of the best. This Idea For Design presents a simple optically isolated linear current loop receiver that uses generic parts. The receiver operates from a single non-isolated power rail (12 V) to generate a convenient analog 5-V voltage-mode output that’s ready for further...
October 2, 2008[Ideas For Design] Use IFDs To Develop And Showcase Your Design Concepts
Electronic Design published my first Idea for Design, “AC-DC Converter Runs Off One Power Supply” (April 16, 1992, p. 93), more than 16 years ago (Fig. 1). It set a theme that I have continued to employ ever since—using the nifty venue of IFDs to present and develop new circuit design ideas and themes to the engineering community. Over the years, examples of some of those basic concepts and ...
October 2, 2008[Ideas For Design] Bidirectional H-Bridge DC-Motor Motion Controller: Backstory
IN APPLICATIONS REQUIRING ABSOLUTE accuracy in the speed control of dc servo motors, there’s no substitute for the traditional tachometerbased feedback loop. But for somewhat less demanding situations, adequate accuracy often can be achieved without the complication and expense of a tach. This can be done by taking advantage of the built-in electromechanical constants of the motor itself. For example,...
October 2, 2008[Ideas For Design] "Take-Back-Half" Convergence Algorithm Stabilizes Microhydro Turbine Controller
THE SOARING COSTS OF fossil fuels, combined with environmental concerns like climate change, are driving the increased interest in renewable (“green”) energy. No energy source is “greener” than hydroelectric power, particularly small (“microhydro”) installations that involve minimal artificial water impoundment and associated environmental impact. Even with an adequate water source, however, efficient and cost-effective implementation of appropriate...
September 25, 2008[Ideas For Design] Optically Isolated 4- To 20-mA Current-Loop Transmitter Is Accurate, Inexpensive
Galvanically (that is, optically or electromagnetically) isolated 4- to 20-mA current loops offer robust noise immunity and tolerate long cable runs. These advantages, combined with simple unshielded two-wire cabling, make this mature signaling standard popular for transmitting analog data in noisy industrial and process control environments. Unfortunately, the conversion of an analog voltage output to an isolated current-loop signal is relatively complicated. In...
October 28, 2002[Ideas For Design] Hyperbaric Fall-Time Viscometer Is PC-Based
The measurement of the viscosity of solutions is an integral element in analytical chemistry and chemical manufacturing. It has particular value in designing and controlling the processes of polymerization, an essential step in the production of...
August 20, 2001[Ideas For Design] 16-Bit PWM Optoisolated DAC Is PC-Controlled
There was a time when an "honest" (e.g., DNL < 1/2 LSB) 16-bit digital-to-analog converter (DAC) was an expensive, premium component. Nowadays they're almost jellybeans—almost. Some applications, however, can still benefit from multichip...
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