Mokhoa oa ho qoba phetiso ea mohala oa phetisetso ho lebelo le phahameng PCB boqapi ba bona

1. Mekhoa ea ho hatella tšitiso ea motlakase

Tharollo e ntle bothateng ba bots’epehi ba lets’oao e tla ntlafatsa ts’ebetsong ea motlakase oa motlakase (EMC) ea boto ea PCB. E ‘ngoe ea bohlokoa ka ho fetisisa ke ho netefatsa hore boto ea PCB e na le motheo o motle. Lera la pontšo le mokato oa lefatše ke mokhoa o sebetsang haholo bakeng sa moralo o rarahaneng. Ntle le moo, ho fokotsa palo ea matšoao a karolo e kantle ea boto ea potoloho hape ke tsela e ntle ea ho fokotsa mahlaseli a motlakase. Mokhoa ona o ka fihlelleha ka ho sebelisa moralo oa “technology” technology “technology build”. Karolo e kaholimo ho sebaka e fihlelleha ka ho eketsa motswako oa likarolo tse tšesaane tsa ho koala le li-micropores tse sebelisetsoang ho phunyelletsa likarolo tsena ho PCB e akaretsang. Khanyetso le bokhoni li ka patoa ka tlase holimo, ‘me letsoalo le lekanang sebakeng ka seng le batla le imenne habeli, ka hona le fokotsa molumo oa PCB. Phokotso ea sebaka sa PCB e na le tšusumetso e kholo holima topology ea ho tsamaisa, ho bolelang hore lupu ea hona joale e fokotsehile, bolelele ba ho tsamaisa makala bo fokotsehile, ‘me mahlaseli a motlakase a batla a lekana le sebaka sa leqhubu la hajoale; At the same time, the small size characteristics mean that high-density pin packages can be used, which in turn reduces the length of the wire, thus reducing the current loop and improving emc characteristics.

2. Strictly control the cable lengths of key network cables

If the design has a high speed jump edge, the transmission line effect on the PCB must be considered. Sekhahla se phahameng sa oache se kopantseng likhomphutha tsa potoloho tse sebelisoang haholo kajeno se thata le ho feta. Ho na le melao-motheo ea mantlha ea ho rarolla bothata bona: haeba li-circuits tsa CMOS kapa TTL li sebelisoa bakeng sa moralo, maqhubu a ts’ebetso a ka tlase ho 10MHz, mme bolelele ba wiring ha boa lokela ho ba kholo ho feta lisenthimithara tse 7. If the operating frequency is 50MHz, the cable length should not be greater than 1.5 inches. Wiring length should be 1 inch if operating frequency reaches or exceeds 75MHz. Bolelele ba lithapo tsa GaAs bo lokela ho ba lisenthimithara tse 0.3. Haeba sena se fetisitsoe, ho na le bothata ba mohala oa phetisetso.

3. Rera ka nepo topology ea cabling

Another way to solve the transmission line effect is to choose the correct routing path and terminal topology. Topology ea cabling e bua ka tatellano ea terata le sebopeho sa mohala oa marang-rang. Ha lisebelisoa tsa mohopolo tse lebelo li sebelisoa, lets’oao le nang le likhahla tse fetohang ka potlako le tla sothoa ke makala a kutu ea lets’oao ntle le hore bolelele ba lekala bo lule bo le bokhutšoanyane haholo. Ka kakaretso, PCB routing o inkela topologies tse peli tsa motheo, e leng Daisy Chain routing le Star kabo.

Bakeng sa mehala ea marang-rang, wiring e qala qetellong ea mokhanni ebe e fihla pheletsong e ngoe le e ngoe ea kamohelo. If a series resistor is used to change the signal characteristics, the position of the series resistor should be close to the driving end. Daisy chain cabling ke eona e molemohali ho laola tšitiso e phahameng ea harmonic ea cabling. Leha ho le joalo, wiring ea mofuta ona e na le sekhahla se fetisisang sa phetisetso ebile ha ho bonolo ho fetisa 100%. Ka moralo oa ‘nete, re batla ho etsa hore bolelele ba lekala ka mohala oa Daisy bo be bokhutšoane kamoo ho ka khonehang,’ me boleng ba bolelele bo bolokehileng bo lokela ho ba: = Trt * 0.1.

Mohlala, lekala le qetella ka lipotoloho tse lebelo tsa TTL le lokela ho ba tlase ho lisenthimithara tse 1.5 bolelele. Tlhaloso ena e nka sebaka se fokolang sa wiring mme e ka emisoa ka se lekanang sa resistor. Leha ho le joalo, moaho ona oa wiring o etsa hore lets’oao le amohelang moamoheli o fapaneng oa lets’oao le se lumellane.

The star topology can effectively avoid the problem of clock signal synchronization, but it is very difficult to finish the wiring manually on the PCB with high density. Ho sebelisa cabler e iketsang ke eona tsela e molemohali ea ho phethela naleli ea linaleli. A terminal resistor is required on each branch. The value of the terminal resistance should match the characteristic impedance of the wire. Sena se ka etsoa ka letsoho kapa ka lisebelisoa tsa CAD ho bala litšobotsi tsa impedance tse ikhethang le litekanyetso tsa ho hanyetsa tse tšoanang.

While simple terminal resistors are used in the two examples above, a more complex matching terminal is optional in practice. Khetho ea pele ke terminal ea papali ea RC. Li-terminals tsa RC tse lekanang li ka fokotsa tšebeliso ea matla, empa li ka sebelisoa feela ha ts’ebetso ea lets’oao e batla e tsitsitse. Mokhoa ona o loketse haholo ts’ebetso ea mochini oa tšupa-nako o ts’oanang le ona. Bothata ke hore bokhoni ba seteisheneng se tšoanang sa RC bo ka ama sebopeho le lebelo la phatlalatso la lets’oao.

The series resistor matching terminal incurs no additional power consumption, but slows down signal transmission. This approach is used in bus-driven circuits where time delays are not significant. Letoto la li-resistor matching terminal le na le monyetla oa ho fokotsa palo ea lisebelisoa tse sebelisoang ka har’a board le segokanyipalo sa likhokelo.

The final method is to separate the matching terminal, in which the matching element needs to be placed near the receiving end. Molemo oa eona ke hore e ke ke ea theola lets’oao, mme e ka ba hantle haholo ho qoba lerata. E sebelisoa haholo bakeng sa matšoao a ho kenya a TTL (ACT, HCT, FAST).

In addition, the package type and installation type of the terminal matching resistor must be considered. SMD surface mount resistors generally have lower inductance than through-hole components, so SMD package components are preferred. There are also two installation modes for ordinary straight plug resistors: vertical and horizontal.

Ka mokhoa o otlolohileng o kenang, ho hanyetsa ho na le phini e khuts’oane e khutsufatsang, e fokotsang ho hanyetsa hoa mocheso lipakeng tsa ho hanyetsa le boto ea potoloho mme e etsa hore mocheso oa ho hanyetsa o hlahisoe habonolo moeeng. Empa tlhomamiso telele paatsepama tla eketsa ho hlohlona sa resistor ena. Horizontal installation has lower inductance due to lower installation. However, the overheated resistance will drift, and in the worst case, the resistance will become open, resulting in PCB wiring termination matching failure, becoming a potential failure factor.

4. Mahlale a mang a sebetsang

Bakeng sa ho fokotsa motlakase o fetang oa phepelo ea motlakase oa IC, decoupling capacitor e lokela ho eketsoa ho chip ea IC. Sena se tlosa tšusumetso ea li-burr phepelong ea motlakase ka nepo le ho fokotsa mahlaseli a tsoang mothapong oa motlakase botong e hatisitsoeng.

Ts’ebetso e boreleli ea burr e molemohali ha decoupling capacitor e hokahane ka kotloloho ho leoto la phepelo ea potoloho e kopaneng ho fapana le mokato oa phepelo ea motlakase. Ke ka hona lisebelisoa tse ling li nang le li-capacitor tse senyehang ka lisoketeng tsa tsona, ha tse ling li hloka hore sebaka se pakeng tsa decoupling capacitor le sesebelisoa se be nyane ho lekana.

Lisebelisoa leha e le life tse nang le lebelo le phahameng la tšebeliso ea matla li lokela ho beoa hammoho ho fihlela moo ho ka khonehang ho fokotsa matla a fetang a nakoana a phepelo ea motlakase.

Ntle le lera la motlakase, lithapo tse telele tsa motlakase li theha sekgoqetsane lipakeng tsa lets’oao le lupu, e sebetsa e le mohloli oa radiation le potoloho e kenang.

Cabling e etsang selopo e sa feteng ka har’a cable kapa marang-rang a mang e bitsoa loop e bulehileng. If the loop passes through the same network cable, other routes form a closed loop. Maemong ana ka bobeli, matla a lenakana (lenakana la mohala le lenakana) a ka hlaha.