Download Anti-interference design principle of the printed circuit board

Anti-interference design principle of the printed circuit board
A cable is fixed up: 1st, try one's best to adjust the wide wire to connect up according to the size of the
electric current. 2nd, the trends of cable , ground wire should keep the same with transmission direction
of the signal . 3, print power input end of plate making should connect electric capacity of decoupling to
have 1000¦ÌF. Two ground wire is fixed up: 1 , figure are separated from simulation. 2nd, the earth
connection should be tried one's best to add thickly, can lack it through permission electric current to
cause in printing plate making of 3 times , should generally reach 2mm . 3, earth connection should is it
form circulation return circuit very much to try one's best, can reduce ground wire electric potential
difference so. The electric capacity is disposed to decouple three times: 1st, print the power input end of
plate making and step the electrolytic electric capacity which connects 1000¦ÌF, can be greater than
100¦ÌF better. 2nd, step the ceramic electric capacity of connecting one 0.01.1¦ÌF between Vcc and GND
of each integrated chip. If the space is not allowed , can dispose the electric capacity of tantalum of one
10¦ÌF for every 40 chips . 3, it is weak to oppose and make an uproar ability, shut off the electric current
and change big device , and ROM , RAM, should be in Vcc and electric capacity that GND decouple
indirectly. 4, restore to the throne end mix with electric capacity of decoupling of 0.01¦ÌF on the " RESET "
in one-chip computer. 5th, decouple the lead wire of the electric capacity can't be too long, can't take the
lead wire in especially high-frequency electric capacity of bypass. Four devices are disposed : 1, clock
generator, brilliant to shake and clock input end of CPU should try one's best close to far away from other
low frequency devices. 2nd, small electric current circuit and big electric current circuit try one's best to
be far away from the logical circuit. 3, print plate making in machine position and direction among the
case , should guarantee above caloric value heavy device in. Five power line , exchange line and signal
line is it leave line power line , exchange line is it assign at the board different from signal line to try one's
best to divide into, otherwise should divide and move the line with the signal line . Whether 6 other
principle. 1st, the bus adds and draws the resistance on about 10K, favorable to anti-interference . 2,
every address line try one's best the same size when connecting up, and try one's best to be short. 3rd,
the line PCB board two sides try one's best to fix up vertically, defend and interfere each other. 4th,
decouple the size of the electric capacity generally fetch C =1 / F, F is the data transmission frequency. 5,
draw resistance (about 10K ) connect Vcc , answer with tube foot that is used on tube foot that does not
need pass. 6th, the components and parts (such as resistance of high-power ) generating heat should
avoid the apt device (such as electrolytic electric capacity ) influenced by temperature . 7th, it have
stronger anti-interference than the line decipher that adopt the whole decipher. In order to control right
little interference of some digital Yuanyuan's circuit of controller of high-power device and digital circuit to
imitating the interference of the circuit, digital ground ' simulation connect to public at connecting placing ,
is it grip the ring of shedding with high frequency to want. This is a kind of cylindrical ferrite magnetisable
material , there are several holes on the axial , get through hole with thicker copper wire , wind and go to
two circles , this kinds of device for low frequency signal can regard as there aren't impedance.. (because
the direct current of the inductance hinders greater, can't use inductance as the high-frequency choke ).
When the signal line beyond the printed circuit board links to each other , usually adopt the shielding
cable. To the high-frequency signal and digital signal, both ends of the shielding cable are grounded, low
frequency shielding cable that analog signal spend, one end earth kind.
And interfere the circuit that
very sensitive circuit or the high-frequency noise is very serious to the noise, should cover the shielding
with the metal and stand up . The high-frequency noise result to 500KHz of ferromagnetic shielding is not
obvious, the thin copper cover shielding result should be better. While using Luo silk and nailing the
regular shielding and covering, the electric capacity has two pieces of function on seven ones that make
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good use of and decouple between the integrated circuit power and ground of electric capacity of
corrosion that the electric potential difference caused when should pay attention to different materials and
is exposed to causes decouple: On one hand an integrated circuit can hold the electric capacity , the
bypass loses the high-frequency noise of this device on the other hand. Electric capacity value is 0.1¦ÌF
that the typical one decouples in the digital circuit. The typical value of the distribution inductance of this
electric capacity is 5¦ÌH. To decouple electric capacity have distribution inductance of 5¦ÌH , to walk
abreast resonance frequency probably in about 7MHz it 0.1¦ÌF, that is to say , as to the thing that the
noise under 10MHz has better result of decoupling , the noise above to 40MHz is nearly inoperative.
Electric capacity of 1¦ÌF , 10¦ÌF, resonance frequency runs side by side in above 20MHz, it is a little better
that the result of getting rid of the high-frequency noise wants.
Electric capacity that every about 10
integrated circuit should add one scene to charge and discharge, or 1 can hold electric capacity , about
10¦ÌF available. You had better not use the electrolytic electric capacity, the electrolytic electric capacity is
that two layers of membrane were rolled, this kind of structure rolled is shown as the inductance in high
frequency. Use the electric capacity of tantalum or gather the electric capacity of carbonic acid ester.
The exertion of the electric capacity is not strict to decouple , can press C =1 / F, namely 10MHz fetches
0.1¦ÌF, 100MHz fetches 0.01¦ÌF.
The pin of the electric capacity should try one's best to be short to
decouple while welding, the long pin will enable decoupling electric capacity will take place and since
resonates. For example porcelain scenes of electric capacity pin length of 1000pF for frequency of
resonance invite 35MHz since at the 6.3mm, pin 32MHz at the long 12.6mm. Decrease 1 of design
principle of anti-interference of the noise and electromagnetic experience printed circuit board that
interfere eight times. Can use bunches of pieces of method of resistance , reduce control circuit from
head to foot along jump speed of turning into.
2. Try one's best to let the electric potential around the
clock signal circuit hasten and is bordering on 0 , enclose the clock district with the ground wire , the clock
thread should try one's best to be short.
3. I/O urges the circuit to try one's best close to printing plate
making. 4. On the shelf door circuit output end unsettled, a on the shelf one is it place correctly input
end take earth to transport, shoulder the input end and connect the output end.
5. Try one's best not to
need the broken line of 90¡ã with the broken line of 45¡ã, connect up it in order to reduce the
high-frequency signal transmission and coupling to the outside.
I/O line smaller than to interfere parallelly on I/O line.
6. The clock thread is perpendicular to
6. The pin of the component should try one's best
to be short. 8. Quartz and sensitive component don't move line very to noise under being brilliant to
shake.
9. The ground wire don't form the electric current cycle around weak signal circuit , low
frequency circuit.
10. While needing , add the high-frequency choke of ferrite in the circuit , separate the
signal , noise , power , ground. Print one on plate making and pass electric capacity that the hole
probably causes 0.6pF; The encapsulation material of an integrated circuit itself causes the distribution
capacity of a 10pF of 2pF; Connecting the plug-in package on a circuit board, there is distribution
inductance of 520¦ÌH; Every one arranges 24 pin integrated circuit sockets inserted directly , introduce
the distribution inductance of a 18¦ÌH of 4¦ÌH. A cable is fixed up: 1st, try one's best to adjust the wide wire
to connect up according to the size of the electric current. 2nd, the trends of cable , ground wire should
keep the same with transmission direction of the materials . 3, print power input end of plate making
should connect electric capacity of decoupling to have 1000¦ÌF. Two ground wire is fixed up: 1 , figure are
separated from simulation. 2nd, the earth connection should be tried one's best to add thickly, can lack it
through permission electric current to cause in printing plate making of 3 times , should generally reach
2mm . 3, earth connection should is it form circulation return circuit very much to try one's best, can
reduce ground wire electric potential difference so. The electric capacity is disposed to decouple three
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times: 1st, print the power input end of plate making and step the electrolytic electric capacity which
connects 1000¦ÌF, can be greater than 100¦ÌF better. 2nd, step the ceramic electric capacity of connecting
one 0.01.1¦ÌF between Vcc and GND of each integrated chip. If the space is not allowed , can dispose the
electric capacity of tantalum of one 10¦ÌF for every 40 chips . 3, it is weak to oppose and make an uproar
ability, shut off the electric current and change big device , and ROM , RAM, should be in Vcc and electric
capacity that GND decouple indirectly. 4, restore to the throne end mix with electric capacity of
decoupling of 0.01¦ÌF on the " RESET " in one-chip computer. 5th, decouple the lead wire of the electric
capacity can't be too long, can't take the lead wire in especially high-frequency electric capacity of bypass.
Four devices are disposed : 1, clock generator, brilliant to shake and clock input end of CPU should try
one's best close to far away from other low frequency devices. 2nd, small electric current circuit and big
electric current circuit try one's best to be far away from the logical circuit. 3, print plate making in
machine position and direction among the case , should guarantee above caloric value heavy device in.
Five power line , exchange line and signal line is it leave line power line , exchange line is it assign at the
board different from signal line to try one's best to divide into, otherwise should divide and move the line
with the signal line . Whether 6 other principle. 1st, the bus adds and draws the resistance on about 10K,
favorable to anti-interference . 2, every address line try one's best the same size when connecting up,
and try one's best to be short. 3rd, the line PCB board two sides try one's best to fix up vertically, defend
and interfere each other. 4th, decouple the size of the electric capacity generally fetch C =1 / F, F is the
data transmission frequency. 5, draw resistance (about 10K ) connect Vcc , answer with tube foot that is
used on tube foot that does not need pass. 6th, the components and parts (such as resistance of
high-power ) generating heat should avoid the apt device (such as electrolytic electric capacity )
influenced by temperature . 7th, it have stronger anti-interference than the line decipher that adopt the
whole decipher. In order to control right little interference of some digital Yuanyuan's circuit of controller of
high-power device and digital circuit to imitating the interference of the circuit, digital ground ' simulation
connect to public at connecting placing , is it grip the ring of shedding with high frequency to want. This is
a kind of cylindrical ferrite magnetisable material , there are several holes on the axial , get through hole
with thicker copper wire , wind and go to two circles , can regard signal this there is for low frequency
kinds of device as there aren't impedance.. (because the direct current of the inductance hinders greater,
can't use inductance as the high-frequency choke ). When the signal line beyond the printed circuit board
links to each other , usually adopt the shielding cable. To the high-frequency signal and digital signal,
both ends of the shielding cable are grounded, low frequency shielding cable that analog signal spend,
one end earth kind. And interfere the circuit that very sensitive circuit or the high-frequency noise is very
serious to the noise, should cover the shielding with the metal and stand up . The high-frequency noise
result to 500KHz of ferromagnetic shielding is not obvious, the thin copper cover shielding result should
be better. While using Luo silk and nailing the regular shielding and covering, the electric capacity has
two pieces of function on seven ones that make good use of and decouple between the integrated circuit
power and ground of electric capacity of corrosion that the electric potential difference caused when
should pay attention to different materials and is exposed to causes decouple: On one hand an
integrated circuit can hold the electric capacity , the bypass loses the high-frequency noise of this device
on the other hand. Electric capacity value is 0.1¦ÌF that the typical one decouples in the digital circuit. The
typical value of the distribution inductance of this electric capacity is 5¦ÌH. To decouple electric capacity
have distribution inductance of 5¦ÌH , to walk abreast resonance frequency probably in about 7MHz it
0.1¦ÌF, that is to say , as to the thing that the noise under 10MHz has better result of decoupling , the
noise above to 40MHz is nearly inoperative. Electric capacity of 1¦ÌF , 10¦ÌF, resonance frequency runs
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side by side in above 20MHz, it is a little better that the result of getting rid of the high-frequency noise
wants. Electric capacity that every about 10 integrated circuit should add one scene to charge and
discharge, or 1 can hold electric capacity , about 10¦ÌF available. You had better not use the electrolytic
electric capacity, the electrolytic electric capacity is that two layers of membrane were rolled, this kind of
structure rolled is shown as the inductance in high frequency. Use the electric capacity of tantalum or
gather the electric capacity of carbonic acid ester. The exertion of the electric capacity is not strict to
decouple , can press C =1 / F, namely 10MHz fetches 0.1¦ÌF, 100MHz fetches 0.01¦ÌF. The pin of the
electric capacity should try one's best to be short to decouple while welding, the long pin will enable
decoupling electric capacity will take place and since resonates. For example porcelain scenes of electric
capacity pin length of 1000pF for frequency of resonance invite 35MHz since at the 6.3mm, pin 32MHz at
the long 12.6mm. Decrease 1 of design principle of anti-interference of the noise and electromagnetic
experience printed circuit board that interfere eight times. Can use bunches of pieces of method of
resistance , reduce control circuit from head to foot along jump speed of turning into.
2. Try one's best
to let the electric potential around the clock signal circuit hasten and is bordering on 0 , enclose the clock
district with the ground wire , the clock thread should try one's best to be short.
try one's best close to printing plate making.
3. I/O urges the circuit to
4. On the shelf door circuit output end unsettled, a on the
shelf one is it place correctly input end take earth to transport, shoulder the input end and connect the
output end. 5. Try one's best not to need the broken line of 90¡ã with the broken line of 45¡ã, connect up
it in order to reduce the high-frequency signal transmission and coupling to the outside. 6. The clock
thread is perpendicular to I/O line smaller than to interfere parallelly on I/O line. 6. The pin of the
component should try one's best to be short. 8. Quartz and sensitive component don't move line very to
noise under being brilliant to shake.
9. The ground wire don't form the electric current cycle around
weak signal circuit , low frequency circuit. 10. While needing , add the high-frequency choke of ferrite in
the circuit , separate the signal , noise , power , ground. Print one on plate making and pass electric
capacity that the hole probably causes 0.6pF; The encapsulation material of an integrated circuit itself
causes the distribution capacity of a 10pF of 2pF; Connecting the plug-in package on a circuit board,
there is distribution inductance of 520¦ÌH; Every one arranges 24 pin integrated circuit sockets inserted
directly , introduce the distribution inductance of a 18¦ÌH of 4¦ÌH. The anti-interference of digital circuit ,
one-chip computer is designed
In the electronic system design, in order to avoid detours and save
time, in conformity with the request of fully considering and satisfying anti-interference, avoid the remedy
that carries on anti-interference after designing finishing. The ones that take shape and interfere have
three basically:
( 1) Interfering the source, it produces the component , equipment or signal interfered to point ,
describe as follows with the mathematics language: Du/dt, di/dt , large place , is to interfere the source .
For instance: Thunder and lightning , relay , silicon controlled rectifier , electrical machinery ,
high-frequency clock ,etc. may all become and interfere the source .
( 2) Propagate the route, mean
that interferes it from interferes the thorough fare or media propagated to the sensitive device in source .
It is through the radiation of conducting and space of the wire that the typical interference propagates the
route .
( 3) Sensitive device, mean the easy target interfered. For instance: A/D, D/A changer, one-chip
computer, digital IC, weak signal amplifier ,etc..
The basic principle designed in anti-interference is:
Suppress and interfere the source, cut off and interfere propagating the route , improve the
anti-interference performance of the sensitive device.
1 suppresses and interferes the source
(similar to the prevention of the infectious disease)
Suppressing and interfering the source is the possible
reducing du/dt which interferes the source , di/dt. This pays the utmost attention to and most important
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principle in anti-interference design, will often get up to the result of getting twice the result with half the
effort. It is mainly realizing through interfering the source both ends and connecting the electric capacity
in parallel to reduce du/dt which interferes the source. The diode flows to realize continuously to reduce
di/dt which interferes the source and interfere the source return circuit and contact the inductance or
resistance and increase.
Suppress the daily measure of interfering the source as follows:
( 1) The relay coil increased and flowed the diode continuously, the ones that produced were
interfered against EMF while dispelling the disconnection coil. Is it flow diode can make to disconnect
time lag behind , increase steady voltage relay movement more number of times within unit time under
diode relay continuously to add only.
( 2) Contact both ends connect spark suppress circuit (contact
circuit RC generally in relay, the resistance generally selects several K to select 0.01uF in electric
capacity to dozens of K), reducing the electric spark influences.
( 3) Add and strain the wave circuit for
the electrical machinery, notice that the electric capacity , inductance lead wire should try one's best to be
short.
( 4) Each one IC wants and connects a 0.01¦ÌF- 0.1¦ÌF high-frequency electric capacity on the
circuit board, in order to reduce IC impact on power. Pay attention to the wiring of the high-frequency
electric capacity , the line and try one's best to be thick to be short close to the end of the power,
otherwise, have meant increasing the equivalent series resistance of the electric capacity, will influence
and strain the wave result.
( 5) Avoid broken line of 90 degrees while connecting up, reduce the
high-frequency noise to launch.
( 6) Silicon controlled rectifier both ends connect RC suppress circuit,
reduce noise that silicon controlled rectifier produce(whether the noise may what silicon controlled
rectifier puncture when being serious).
Can be divided into and conducted interfering and radiation two
kinds of interference according to the spread route interfered.
The so-called interference of conducting
and interfering refering to propagating to the sensitive device through the wire. High frequency interferes
the noise different from frequency band of the useful signal, can cut off high frequency and interfere the
spread of the noise through the method to increase the wave filter on the wire , can add and isolate the
photosensitive resister to solve sometimes. The danger of the noise of the power is the greatest, pay
special attention to dealing with. The so-called radiation interferes meaning that propagates to the
interference of the sensitive device through space radiation. The general solution is increasing and
interfering the distances of the source and sensitive device, isolate them with the ground wire and add on
the sensitive device and cover covering. 2 cuts off the daily measure of interfering propagating the route
as follows:
( 1) Fully consider the impact on one-chip computer of the power . The power is made well, the
anti-interference of the whole circuit solves the big half. A lot of one-chip computers are very sensitive to
the noise of the power , should add and strain the wave circuit or the voltage stabilizer for the one-chip
computer power , in order to reduce the interference to the one-chip computer of power noise. For
example, can utilize magnetism pearl and electric capacity make up ¦Ð shape strain wave circuit ,
condition certainly can replace the magnetism and pearl with 100¦¸ resistance when expecting much.
( 2) If mouth of I/O of the one-chip computer is used for controlling noise devices , such as electrical
machinery ,etc. , should add and isolate between I/O mouth and noise source (increase ¦Ð's shape and
strain the wave circuit). Control noise devices , such as electrical machinery ,etc., should add and isolate
between I/O mouth and noise source (increase ¦Ð's shape and strain the wave circuit).
( 3) Pay
attention to shaking brilliantly and connecting up. Shake brilliantly and try one's best to near with the
one-chip computer pin, is it stand up to isolate by district with ground wire clock, brilliant to shake outer
cover earth and regular. This measure can solve a lot of knotty problems .
( 4) The dividing area
rationally of circuit board, such as strong , weak signal, the figure, analog signal. As much as possible
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interfere source (such as the electrical machinery , relay ) far away from the sensitive element (such as
the one-chip computer ).
( 5) Isolate the digital district from simulation district with the ground wire , the
figure should be separated with simulation, connect on the power ground in some finally. A/D, D/A chip
connect up to take this as the principle too, the producer assigns A/D, D/A chip pin to consider this
request while arranging .
( 6) The ground wire of one-chip computer and high-power device should be
grounded alone, in order to reduce and interfere each other. The high-power device is placed on the
board edge of the circuit as much as possible .
( 7) In the one-chip computer I/O mouth, the key
places , such as the cable , the board connecting wire of the circuit ,etc. use the anti-interference
component such as magnetism and pearl , magnetic ring , power wave filter, the shielding is covered, can
improve the anti-interference performance of the circuit notably . 3 improves the anti-interference
performance of the sensitive device
Improve sensitive anti-interference of device performance
mean consider trying one's best to reduce from sensitive device here to interfering the picking up of the
noise, and never the method that the normal condition resume as soon as possible. Improve the
sensitive performance daily measure of device anti-interference as follows:
( 1) Try one's best to reduce the area of the return circuit ring while connecting up, in order to
reduce the reaction noise.
( 2) While connecting up, the cable and ground wire should try one's best to
be thick. Besides reducing and pressing and lowering , the more important thing is that reduces the
coupling noise.
( 3) As to I/O mouth that one-chip computer leave unused, don't unsettled, take earth
or connect the power. Other stand-by in change system earth under the logic situation or connect the
power end of IC.
( 4) Control and guard the gate in dog's circuit to the thing that the one-chip computer
uses the power , for instance: IMP809, IMP706, IMP813, X25043, X25045,etc., can improve the
anti-interference performance of the whole circuit by a large margin .
( 5) On the premise of can meet
the demands in speeding , try one's best to reduce shaking and selecting the digital circuit of low-speed
for use brilliantly of the one-chip computer.
( 6) IC device tries one's best to weld on the circuit board
directly, use little Block ICs. I talk about my experience in this respect first :
Software respect: 1st, I get used to becoming code space used clearly completely " 0 " of, in NOP
because of this equivalent, can playback when the procedure runs and flies ; 2nd, add several NOPs ,
the purpose and 1 before jumping the order of rotating; 3rd, can adopt software simulation WatchDog
while there is no hardware WatchDog, in order to monitor the operation of the procedure; 4th, when
involve dealing with the outside device parameter and adjust or set up , in order to prevent the outside
device from making mistakes and can send the parameter once again regularly because of interfering, in
this way , can make the outside device resume as soon as possible being correct ; 5, anti-interference in
the communication, can add the data check-up location , can adopt 3 and fetch 2 or 5 and fetch 3 tactics ;
6th, while there are communication lines, such as me ^ 2C , make by the strategic hinterland of China, we
find put Data line , normality , line of CLK and line of INH for being high in being real, its anti-interference
result should be better than putting for being low. Hardware: 1st, the department line of ground wire ,
cable is certainly important! 2, the uncoupling of the circuit; Part of 3 , counting , mould ground; 4th,
each digital component takes electric capacity 104 between ground and power ; 5, have application
occasion of relay , at the big electric current , defend relay contact spark interference to the circuit, can
combine 1104 and diode among the relay coils , and often indirect electric capacity 472 of beginning on
the contact, the result is good!
6, disturb for bunch which defends I/O mouth , can isolate I/O mouth ,
there are the methods diodes are isolated, the door circuit is isolated, the light is isolated occasionally ,
isolates etc. electromagnetically; 7, certainly the anti-interference of large plywood must be better than
the single panel , but cost is high several times.
8, the device choosing a anti-interference to be with
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strong ability is more effective than any method of it, I think this point should be the most important.
Because the innate deficiency of the device is very difficult to remedy with the external method , it is the
getting more expensive a bit to be strong in anti-interference but not often ability , anti-interference the
bad in ability should, cheaply but performance give a great discount just as Dongdong of Taiwan! See
everybody's application occasion mainly. The printed circuit board (PC8 ) is support one of circuit
component and device in electronic product. It offers the joining electrically between component and
device of circuit. With the development at full speed in technology of electricity, the density of PGB is
higher and higher. The quality that PCB designs confronts with each other and interferes ability to exert a
tremendous influence. So, while carrying on PCB design. Must observe the general principle that PCB
design , and in conformity with the request of according with anti-interference to design.
Place connecting type ¡ûEarth purpose ¡ûEarth function, so which kind of places
connecting type are adopted, depend on which kind of ground ground is, what is this kind
in purpose in function of ground, two problem these solve, connect place type but success
will come after conditons are ripe.
The earth purpose has determined the place connecting type. The same circuit, different
purposes , may all adopt different connecting the place type . This view will certainly be
remembered. Such as the same circuit, use on portable equipment, the static is
accumulated and can not discharge, the earth purpose is that the ground electric potential
is balanced ; Use on equipment not portable, will generally have a safe earth measure, the
earth purpose to discharge to the static is to lead open impedance low enough, especially
lead open impedance to the high frequency of the spike pulse.
Precautions of person who explain divide into odd independent views recommend
separately, the simple in though the every piece one content ,it propose it sure read by N
repeatedly all over,the more alike to face by a cup of tea not fines, let heartbeat in 60bpm
following state , detailed detailed product , feel the aesthetic feeling and intension among
them. Then may just realize the deep reason from the simple word .
Divide from performance , the earth dividing into four:
Safe earth , job earth (digital ground , simulation ground , power device ) , defend wave
well up earth (strike by lightning wave well up , have electric wave not to well up ) , defend
static earth.
Has spoken in the previous document, " the earth purpose has determined the place
connecting type ", the purpose refers to the function of its realization promptly. All earth
can sum up in the point that basically that come inside these four kinds . Each earth first
clear to should ground where one does it belong to.
It is that earth pursue goal for impedance to be the low, steady, balanced
The ground is low and very easy to understand in impedance, use thick cable , have one
question can ignore certainly, for example I pass one great inductance earth, if ground
fluctuation of electric current that ground wire run frequency 0.00000001Hz, the great
perceptual effect of inductance behave on very much obvious, has equated with and has
been grounded directly, but fluctuate the electric current were 1,000,000Hz, induction
reactance =j ¦Ø L =J 2 ¦Ð f L, seems very great, in this case, it is very bad to be equivalent
to and grounded high-frequencily. Every reader may say , you mess things up you, who
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could use a great inductance earth, first, will have this way under a certain state, second
connect pieces of inductance like this, to walk line inductance be can't ignored either
under high frequency ordinary cable. Summarize for a word, the high-frequency earth of
earth ¡Ù of low frequency. Namely low earth of impedance take analysis high frequency or
earth of low frequency.
The ground stability is more easy to understand, generally speaking,earth if there is
getting lower enough impedance, rush down electric current it put easy, can produce what
son is it lower to press , like one oversize electric capacity at bottom line, the ocean of the
electric charge, have limitlessly broad mind , come in to remain calm more or less.
The ground is balanced easier to be ignored , to a signal, the useful part is two pieces of
difference of pressing on the line, if the ground wire drifts about, two pieces of pressing the
rising or decline with equal difference to ground wire on the line, namely the value of
model's voltage of difference remains unchanged, the voltage of the mould changes
altogether, in fact the function of the circuit is realized as usual. Just as increase
accordingly, your high 3cm than I, stand on the ship, the ship has gone up, you are still still
high my 3cm. The situation when the static is protected daily to reach, one static pulse get
to circuit at the board through air, to some circuit, the difference of the distance is certain
to result in producing the difference of pressing of electrostatic induction. Separated with a
metal sheet at this time, even metal sheet this float empty, to the circuit board behind the
metal sheet, reaction will be a even electric field , though the inductive interference still
exists, on the circuit is basic equilibrium at least. Certainly if this metal sheet is better in
earth. Certainly the voltage of the mould will seldom keep living altogether, because it is
not even to transmit the impedance of the line, often it can have changed into difference
mould interfere the voltages, you had better not let us of balanced problem in the face of,
in the method of having , such as person who float equipment , have the circuit board that
the static bludgon into, balanced question of consideration that shelter wants at time.
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