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Review of Jim Williams: AN43 Bridge Circuits

Download AN43 Bridge Circuits (1990, Linear Technology, 48 pages, 3.63 MB pdf file)

AN43 starts with a discussion of signal conditioning techniques for bridge circuits. Figure 4 (p.3 - 4) gives a good overview of several configurations and their advantages and disadvantages. On the next pages several applications are shown, e.g. for the precision measurement of temperature and strain. Very interesting is the discussion of Wien bridge based oscillators (p. 29 - 33). Williams presents several variants of these circuits, aiming for the lowest possible distortion. On page 33 he finally shows a circuit (figure 49) with 3ppm distortion, "below the noise floor of most analyzers". You can find some more details about this circuit (and its history) in Analog Circuit Design, chapter 7, p.43. You might notice that in the book the LT1028 is used instead of the LT1115 - don't worry too much, the specs of both parts are quite similar. Appendix D, p.44 - 46 of AN43 discusses distortion measurements in general. In his last app note AN132 Fidelity Testing for A-D Converters Williams returned to the Wien bridge.

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

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