However, the following two examples show that, in practice, most of today’s signal processing ICs are really “high-speed,” and must, therefore, be treated as such in order to maintain high performance. With respect to ADCs and DACs, the sampling (or update) frequency has generally been used as the distinguishing speed criterion. In the past, “high-precision, low-speed” circuits have generally been viewed differently than so-called “high-speed” circuits. Maintaining a wide dynamic range with low noise in a hostile digital environment is dependent upon using good high-speed circuit design techniques, including proper signal routing, decoupling, and grounding.
Requirements for processing analog signals that have a wide dynamic range impose the need to use high-performance ADCs and DACs. Today’s signal processing systems generally require mixed-signal devices, such as analog-to-digital converters (ADCs) and digital-to-analog converters (DACs), as well as fast digital signal processors (DSPs). Indeed, the single issue of quality grounding can-and must- influence the entire layout philosophy of a high-performance mixed-signal PCB design. Proper conductor routing and sizing, as well as differential signal handling and ground isolation techniques, enable control of such parasitic voltages.Īn important topic to be discussed is grounding techniques appropriate for a mixed-signal, analog/digital environment. These voltages can be due to external signal coupling, common currents, or, simply, excessive IR drops in ground conductors. Some other aspects of grounding that must be managed include the control of spurious ground and signal return voltages that can degrade performance. Since this factor is one of the more significant advantages to PCB-based analog designs, appreciable discussion here is focused on it. Fortunately, certain principles of quality grounding, especially the use of ground planes, are intrinsic to the PCB environment. Grounding is an issue for all analog designs, and it is a fact that proper implementation is no less essential in PCB-based circuits.
Improper application of grounding strategies can cripple performance in high-accuracy linear systems. Unfortunately, it has also become the return path for the power-supply current in unipolar supply systems.
Unfortunately, there is no “cookbook” approach that will guarantee good results, and there are a few things that, if not done well, will probably cause headaches.įor linear systems, the ground is the reference against which we base our signal. While the basic concepts are relatively simple, implementation is very involved. Grounding is undoubtedly one of the most difficult subjects in system design.
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