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5.2.4. Decoupling

The influence of digital circuits on analog circuits is widely known. Therefore, an appropriate separation of the power supply and an appropriate running of the ground tracks will avoid serious problems in mixed analog-digital circuits. It is required that both analog and digital signals have different return paths as can be seen in figure 29. To this end, some of our products have 5 V outputs for digital circuits and ±15 V for analog circuits, with galvanic isolation. The analog and digital grounds should be joined at one single point, which should normally be closer to the devices common to the analog and digital circuits such as A/D or D/A converters. If several earthing points are required, these should be as close as possible to one another building a large common ground point. Another good strategy is to decouple the devices using ceramics and electrolytic or tantalum capacitors in parallel and placed as close as possible to the integrated circuit, causing the signal loop to have the shortest path possible, thus preventing cross-talk problems between multiple loads.