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发表于 2007-7-22 21:43:36
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资料是一流的,我在2004年看过,分四部分.是英文的.请搂住降价到5元以下.否则我会卖 2元.
E.M.C. COUPLINGS
MAR 2004
COMMON IMPEDANCE COUPLING
Basic amplification line
Each amplifier stage
amplifies the voltage difference
between a hot line and the cold line
known as reference or ground
If a high current or fast signal circuit shares this ground it may develop in it some parasitic
voltage which adds to the useful one , and spoils the complete amplification line .
The ground lines must be as low impedance as possible , care must be taken to separate noisy circuits from sensitive circuits at gound level .
Good ground planes are necessary .
CHASSIS TO BOARD CAPACITIVE COUPLING
Capacitive coupling :
Two neibouring conductors build a capacity (electricity reservoir)
The higher the frequency the higher the current in a capacitor
How to make one of the capacitior plate « inactive »
Simply by inserting an intermediate plate (screen) connected
to the plate which becomes inactive (the upper one here),
this creates a secondary capacitor « through » which the current
flows
One can understand that any track on a printed circuit may act as a capacitor with the chassis
Especially when considering high frequency disturbances .
To avoid this « sensitive track to chassis capacitor » a screen connected to the 0v must be
installed . (see micro computeurs)
INDUCTIVE CROSS TALK COUPLING
A variable current flowing in a loop (nearly always the case) generates a magnetic field , when
this field circulates through another open loop , it creates a voltage at the terminals .
This is the transformer principle
This kind of schematic may happen
unintentionally on boards and also
between cables .
use
flat independant loops
(with reduced surface)
One return for each loop
Better situation
if conductors are against
the conductive structure
(with reduced surface)
The conductive structure may surround the conductors
An additional short circuit
(closed loop ,connection at both ends)
will cancell the magnetic field ,
no induction will take place in
the victim loop
Use ground plane and supply plane between uncompatible signals
and paths at right angle crossings |
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