How to ground and power complex circuits

As electronics applications continue to become more compact and has more and more features in same package (think about modern smart phone or tablet), requires system engineers to use multiple power rails and mixed disciplines of circuit design (mix both analogue and digital parts tightly). A typical tablet will consist of items such as a backlight, touch screen, camera, charging system (USB and Wireless), Bluetooth, Wi-Fi, audio outputs (speaker, headphones), and memory for storing data.

Circuits with analog and digital signals tend to cause declaration of several ground references,  often leading to a spaghetti-like result, where ideas are distorted and what appear to be solid solutions turn out to be  chaotic failures. In order to put engineering foundations back into complex systems, it is imperative that power and grounding solutions are proactively engineered in a manner that optimizes performance and heat dissipation while reducing EMI radiation and signal to noise interference.

How to ground and power complex circuits article demonstrates how to optimize complex circuits from the point of view of power delivery, improved signal integrity and properly grounded functional blocks to implement the final system.  The focus is on understanding circuit needs and pre-planning for the final system, because the result of those two steps is a project that effectively moves  from the schematic to the final printed circuit board.  Any signal (or power supply) used to drive any circuit must be given a proper path to return to its source so circuit designers must consider the source and grounding schemes.

Understanding current flow and the concept of minimizing current loops leads to the obvious conclusion that the single GND method is ideal and preferred as a PCB design approach because it significantly reduces component count, layer count, and potential radiation. Every trace and block will be provided the shortest return path possible on the PCB.  By following this guidance, the system designer will only have to control the PCB design from the perspective of proper trace widths as well as smart placement of components and blocks.

The decision regarding single or multiple planes should always be guided by the visualization of return paths.The the single ground plane approach, in most case it is the best one, as it simplify the PCB layout, it lower ground noise and it lower electromagnetic emission.

2 Comments

  1. Tomi Engdahl says:

    Monitor Ground Fault Leakage Currents
    http://ecmweb.com/content/monitor-ground-fault-leakage-currents

    Most power quality problems are due to incorrect connections of an electrical system. Using CTs and leakage current monitors, you can check an electrical system during acceptance testing of the installation and also during maintenance and renovation of the system. Watch out for partial or complete short circuits between neutrals and your grounding network. They’ll often create power quality disturbances

    Most power quality problems are due to incorrect connections of an electrical system. Using CTs and leakage current monitors, you can check an electrical system during acceptance testing of the installation and also during maintenance and renovation of the system.

    Yes, there’s a certain amount of normal leakage current going from the neutral and the phase conductors to ground in all electrical systems. Usually, the level of this leakage current is from about 10mA to some 100mA, depending on the size of electrical system.

    Voltage differences are between different grounding points.

    Because of contact between the neutral and ground at Point A, the return current flowing from the load also flows through the grounding network and the grounding circuits in Devices D1 and D2.

    This current may disrupt their operation because the voltage difference and resulting current are often quite high.

    So, how does ground noise enter a sensitive electronic device? Current flowing in a neutral conductor consists of many kinds of disturbances such as harmonic waves and distortion, high frequency disturbances, transients, etc.

    As you can see, a filter or surge suppressor circuit does not prevent disturbances from entering the device. Often sensitive electronic devices are connected to a reference ground. The problem above results from the devices’ grounding conductor connected to the conduit (which is also serving as a ground) rather than to a dedicated reference grounding system tied to the main grounding point.

    Sometimes the shield of the communication or data cable connects to conductive parts of the building.

    Watch out for magnetic field interference. In a normal electrical system, ground current produces a low frequency (60 Hz) magnetic field. At this frequency, a clean electrical system has a magnetic field between 0.1 mGaus to 45 mGaus. In an industrial working environment the magnetic flux density can be much higher, anywherefrom 20 mGaus to 15 Gaus. Normal sources of stray magnetic fields are transformers, large motors, and various industrial production machines. However, the major significant cause for magnetic stray fields is often a faulty grounding connection or an equipment failure in an electrical system.

    Relatively small magnetic fields cause disturbances to sensitive electronic devices. For example, fields higher than 13 mGaus can disturb a computer monitor.

    In the U.S., definitive standards on electric magnetic fields aren’t yet established. However, in Europe, the Cenelec (European Committee for Electrotechnical Standardization) EMC Standard EN-50082-1 gives limit values for residential, commercial, and light industry environments. The maximum value of magnetic flux density is 38 mGaus for industrial situations and 13 mGaus for computer monitoring locations. In a facility’s electrical system, you may see very high peaks of magnetic flux density during starting current impulse. These peaks can directly effect the circuits of sensitive devices.

    How do you monitor ground leakage current to avoid problems? To prevent electronic noise from disturbing electronic devices, you can use different kinds of noise attenuation circuits, such as filters, isolation transformers, photo-couplers, etc. But one of the most important aspects in preventing electronic noise from disturbing electronic devices is to evaluate the wiring and grounding systems first. This can often be expensive and time consuming. The simplest and most economical method is to continuously monitor leakage current of the whole electrical system or the most critical parts of electrical system.

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  2. Tomi Engdahl says:

    Properly ground your circuits
    http://www.edn.com/design/pc-board/4443239/Properly-ground-your-circuits?_mc=NL_EDN_EDT_pcbdesigncenter_20170109&cid=NL_EDN_EDT_pcbdesigncenter_20170109&elqTrackId=d932d2ce2aad46adbca013bcf5b3cd6f&elq=a88a909087f549c2a4ded0b4dfc1c1e3&elqaid=35442&elqat=1&elqCampaignId=30989

    Engineers use the word “ground” in every electronic circuit to denote some part of a system or structure that is “neutral,” or zero potential. Unfortunately, we often think of circuits and systems, especially those with both analog and digital signals, as having more than one ground. This concept gave rise to a recent discussion on a signal-integrity online community

    The kinds of grounds mentioned in this discussion include:

    Logic ground
    Analog ground
    Chassis ground
    Safety ground
    Earth ground

    Methods proposed for connecting these various “grounds” cover a broad range of options including:

    Connecting them at only one point.
    Cutting the ground plane under a mixed signal component
    Connecting them with capacitors.
    Segmenting the ground plane in a PCB such that there is only a narrow connection at one place between the analog and digital sides of the design.
    Separating the analog and digital grounds.

    Figure 1. Digital logic ground symbol seen in most schematic diagrams.

    These seemingly conflicting methods for dealing with ground can be a bit confusing.

    Digital logic ground is the “reference” terminal of a power supply for your digital logic. For most digital logic systems, it’s the negative terminal of the logic power supply

    Analog ground is the reference terminal of the supply that powers an analog circuit.

    Chassis ground is the name given to the connection of the safety wire from the AC mains to a product’s case. It gets this name because the case of a product is often called the chassis. This wire is usually the green wire in an extension cord

    Sometimes, EMI engineers erroneously refer to this “Chassis ground” (Figure 3) as a place that has some function in the containment of EMI. This statement never has or never will be based on fact because it has no role in this part of an electronic design.

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