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Review of Grant, Wurcer: AN348 Avoiding Passive Component Pitfalls

Download AN348 Avoiding Passive Component Pitfalls (1983, Analog Devices, 6 pages, 931KB pdf file)

This is a famous and often quoted app note that clearly explains why even such "humble" components as resistors, capacitors and even the printed circuit board have to be carefully selected and analysed if one wishes to design a high precision circuit.

For the capacitor, the equivalent circuit is shown and the parasitic elements explained, also temperature effects. Dielectric absorption is discussed in detail, some special problems with different kinds of capacitors are also mentioned. For the resistor, temperature coefficients and thermoelectric effects are discussed. A rarely mentioned resistor phenomenon is temperature retrace (p. 4, 3rd paragraph): A 10ppm effect is certainly easy to overlook, but if highest precision is demanded, it is good to know about it. Parasitic effects, aging and noise are also discussed.

The discussion of problems with printed circuit boards mentions absorbtion of atmospheric moisture, surface leakage through residues and how you can avoid them by proper washing procedures. By the way, in Troubleshooting Analog Circuits Bob Pease reports how he cleaned some printed circuit boards in a dishwasher with calgonite (p. 54, the book contains some more good information about printed circuit boards and also about resistors and capacitors). The app note also discusses the important technique of guarding sensitive nodes and the effects of dielectric absorption on printed circuit boards.

If you know the Analog Devices Seminar Notes, you will probably have seen parts of AN348 in some of them - there is a lot of overlap between the various Analog Devices publications (and as long as you get them for free there is nothing wrong with this). Very interesting is Chapter 7 Hardware and Housekeeping Techniques of Op Amp Applications. Section 7-1 Passive Components and Section 7-2 PCB Design Issues are partly based on AN348 but contain much more information, a good list of references and also some links.

You may also be interested in some other recommendations for Resistor Resources and Capacitor Resources.

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