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Avoiding Noise


General tips for avoiding noise

avoiding noise in a wire-wrap circuit
(yes, we know no one wire wraps anymore, but the lessons learned under those less than ideal conditions are worth remembering)

avoiding noise in a PCB

one solid unsplit ground plane

ground loops

other ways of avoiding noise

General tips for avoiding noise

Given a choice between your chips not agreeing on where ground is and on not agreeing on the supply voltage, its better that they agree on ground. That can help a bit with noise problems. <GRIN>

Avoiding noise in wire-wrap circuits

Follow these steps to eliminate noise.

Avoiding noise in a PCB

one solid unsplit ground plane

There seems to be a bit of controversy between " power isolation " vs others who say "Don't split the ground plane. Don't split the power plane either, unless it actually needs to be different voltages. PCBs@"

Bryan in 1998 made some good recommendations, including "Make sure that you have a good ground plane under anything that uses RF frequencies especially the micro controller and I/O lines. ... Some people use a split ground plane but I have had disastrous results using a split ground plane." -- "RF Noise" thread http://massmind.org/techref/postbot.asp?by=thread&id=RF+Noise

"Do not split the ground plane. Use one solid plane under both analog and digital sections of the board." -- Ott, in article "partitioning and layout of a mixed signal pcb" article by Henry W. Ott (EMI consultant) in _printed circuit design_ magazine (june 2001) http://www.hottconsultants.com/techtips/split-gnd-plane.html http://www.hottconsultants.com/pdf_files/june2001pcd_mixedsignal.pdf /* was http://www.pcdmag.com/db_area/archives/2001/06/0106_1.html */

in it he basically makes the case that split planes are generally a bad thing

their best use he says is to correct a badly laid out board after the fact and also in some cases they are needed for safety isolation

but as to localizing noise (preventing polution of low level signals) and minimizing EMI nothing beats a *properly laid out* (i.e. 'routed/placed') board with a single ground plane possessing a single net

-- recc. Dennis Saputelli 2001-06-09

"Nothing is more important to the system design of a circuit than having a solid and complete power system. ... Design the ground system to include as many parallel pathways to ground as possible. ... ground planes are optimal ..." -- Mark Glenewinkel. "Motorola Semiconductor application note AN1259: System design and layout techniques for noise reduction in MCU-base systems". 1995.

US Patent 6023202 "Ground return for high speed digital signals that are capacitively coupled across a DC-isolated interface" by Hill, Gregory A. (02/13/1998) describes the best way to capacitively couple high-speed digital signals (in general) across a galvanic isolation, and (specifically) how it applies to FireWire. "... application of the invention produces improved signal integrity, reduced generation of electromagnetic emissions, and reduced susceptibility to electromagnetic interference."

"Analog-to-Digital Converter Grounding Practices Affect System Performance" http://www.ti.com/litv/pdf/sbaa052 describes how "a single ground plane" works best. Attempting to make a "split grounds connected together at the ADC" gave worse DLE.

ground loop

"Ground loops" are a badly misunderstood part of electronics.

Many op-amp data sheets recommend guard rings, such as

other ways of avoiding noise in a PCB

Books:

See also:


file: /Techref/noises.htm, 14KB, , updated: 2014/4/30 10:47, local time: 2014/11/23 17:21,
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