By using low-cost microprocessors and a program-controlled numerical-integration technique, you can achieve good noise rejection and take full advantage of the higher speeds offered by recently developed dual-slope A/D converters such as the TC7109. This and similar converters overcome the speed limitations imposed by logic-gate and analog comparator delays in earlier dual-slope devices, and the modern units can operate at rates as high as 30 to 100 samples/sec. Nevertheless, operating them at their maximum conversion rates often makes it difficult or impos- sible to achieve the high normal-mode line-frequency rejection that dual-slope A/D converters inherently offer at slower conversion rates. Thus, noise considerations have often precluded use of these converters at their rated speeds — especially in industrial environments, where line-frequency and other low-frequency noise components can be a particular problem. AN788 Numerical-Integration Techniques Speed Dual-Slope A/D Conversion The integrating A/D converter integrates the signal only in a certain Author: Gary Grandbois and Wes Freeman, time window, as Figure 1b shows. This limited integration period Microchip Technology, Inc. results in normal-mode noise rejection only when the integration ……