A ground-loop in an electrical system, is an unwanted current that flows
in a conductor connecting two points that are nominally at the same
potential, i.e., ground, but are actually at different potentials. For
example, the electrical potential at different points on the surface of
the Earth can vary by hundreds of volts, primarily from the influence of
the solar wind. Such an occurrence can be hazardous, e.g., to personnel
working on long grounded conductors such as metallic telecommunications
cable pairs.
A ground loop can also exist in a floating ground system, i.e., one not
connected to an Earth ground, if the conductors that constitute the
ground system have a relatively high resistance, or have, flowing through
them, high currents that produce a significant voltage (IxR) drop. Ground
loops can be detrimental to the operation of the electrical system.
Contrast with ground current.
There are three fundamental grounding techniques;
1. Floating Ground System: The ground plane is not returned to
earth.
2. Single-Point Grounding System: A single
physical point in the circuitry is designated as a ground reference
point.
3. Multipoint Grounding System: The ground plane is taken to
earth, effectively taking each point connected to the ground plane to
earth.
Refer to MIL-HDBK-1857, Grounding, Bonding and Shielding Design Practices
Minimizing
RF PCB electromagnetic emissions
{Sean Mercer, Ph.D., C.Eng: www.rfdesign.com}
ANTENNAS,
Frequently Asked Questions
{Virtual Technologies, Ltd. }
A power plane at RF will act like a patch antenna, spreading spurious signals all over the Printed wiring board. An unintended antenna connection.
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Design Rules: 1: Stack power planes next to ground planes so they capacitively couple. Coupling the power plane to the ground plane reduces the number of by-pass capacitors required in the circuit. 2: When possible use wide traces for power and ground. Thicker traces reduce the trace impedance and allow the line to carry higher current loads. 3: Avoid placing slots in ground planes. Slots in ground planes force the current to flow around the slot, separating the return current from it signal trace. Slots may be placed at the edges of the board where signal trace aren't run. 4: Avoid Ground Loops when possible, and avoid ground loops in low-level, low-frequency circuits. A ground loop is an unwanted current loop. The current flowing in the loop generates additional noise and provides no benefit to the circuits operation. 5: Board Stack-up; |
Chart of
PWB External Etched Copper Current Capacity: current rating based on
trace cross section in square mils, temperature rise and current in
amperes.
Chart of
PWB Internal Etched Copper Current Capacity: current rating based on
trace cross section in square mils, temperature rise and current in
amperes.
Graphic of Minimum
Annular Ring, What is a Minimum Annular Ring.
Graph of PWB
Ground Potential, moving away from a single point ground connection
[example].
Electronic Chassis
Grounding
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