Cara ngindhari efek saluran transmisi ing PCB kacepetan dhuwur desain

1. Cara kanggo nyegah gangguan elektromagnetik

Solusi sing apik kanggo masalah integritas sinyal bakal nambah kompatibilitas elektromagnetik (EMC) papan PCB. Salah siji sing paling penting yaiku supaya papan PCB duwe landhesan sing apik. Lapisan sinyal kanthi lapisan lemah minangka metode sing efektif banget kanggo desain kompleks. Kajaba iku, minimalake Kapadhetan sinyal lapisan paling njaba ing papan sirkuit uga minangka cara sing apik kanggo nyuda radiasi elektromagnetik. Cara iki bisa dipikolehi kanthi nggunakake desain PCB “build-up” teknologi “build-up” teknologi. Lapisan area lumahing digayuh kanthi nambah kombinasi lapisan insulasi lancip lan mikropor sing digunakake kanggo nembus lapisan kasebut ing PCB proses umum. Resistansi lan kapasitansi bisa dikubur ing ngisor permukaan, lan kapadetan linear saben area meh meh tikel, saengga bisa ngirangi volume PCB. Pangirangan area PCB duweni pengaruh gedhe ing topologi nuntun, sing tegese loop saiki dikurangi, dawa perutean cabang dikurangi, lan radiasi elektromagnetik kira-kira sebanding karo area loop saiki; 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. Kripik sirkuit integral kanthi cepet yen wis digunakake saiki luwih akeh masalah. Ana sawetara prinsip dhasar kanggo ngatasi masalah iki: yen CMOS utawa sirkuit TTL digunakake kanggo desain, frekuensi operasi kurang saka 10MHz, lan dawa kabel kudu luwih saka 7 inci. 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. Dawa kabel maksimal kanggo Kripik GaAs kudu 0.3 inci. Yen iki ngluwihi, bakal ana masalah jalur transmisi.

3. Rencana topologi cabling kanthi bener

Cara liya kanggo ngatasi efek jalur transmisi yaiku milih jalur rute lan topologi terminal sing bener. Topologi cabling nuduhake urutan kabel lan struktur kabel jaringan. Nalika piranti logika kanthi kecepatan dhuwur digunakake, sinyal kanthi ujung sing ganti kanthi cepet bakal distorsi dening cabang batang sinyal kajaba dawa cabang tetep cekak banget. Umumé, nuntun PCB nganggo rong topologi dhasar, yaiku Daisy Chain nuntun lan distribusi Star.

Kanggo kabel chain daisy, kabel diwiwiti ing ujung driver lan tekan saben pungkasane nampa. Yen resistor seri digunakake kanggo ngganti karakteristik sinyal, posisi resistor seri kudu cedhak karo ujung nyopir. Kabel rantai Daisy paling apik kanggo ngontrol gangguan harmoni sing dhuwur saka kabel. Nanging, kabel jinis iki duwe tarif transmisi paling murah lan ora gampang dilewati 100%. Ing desain nyata, kita pengin nggawe dawa cabang ing kabel rantai Daisy secepat mungkin, lan nilai dawa sing aman yaiku: Stub Delay < = Trt * 0.1.

Contone, cabang mungkasi sirkuit TTL kanthi kecepatan dhuwur kudu kurang saka 1.5 inci. Topologi iki mbutuhake papan kabel sing kurang lan bisa dipungkasi kanthi cocog siji resistor. Nanging, struktur kabel iki nggawe sinyal sing ditampa ing panampa sinyal sing beda ora sinkron.

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. Nggunakake cabler otomatis minangka cara paling apik kanggo ngrampungake cabling bintang. A terminal resistor is required on each branch. The value of the terminal resistance should match the characteristic impedance of the wire. Iki bisa ditindakake kanthi manual utawa liwat alat CAD kanggo ngetung nilai impedansi karakteristik lan nilai resistensi terminal sing cocog.

While simple terminal resistors are used in the two examples above, a more complex matching terminal is optional in practice. Pilihan pertama yaiku terminal match RC. Terminal sing cocog karo RC bisa nyuda konsumsi daya, nanging mung bisa digunakake nalika operasi sinyal cukup stabil. Cara iki paling cocog kanggo pamrosesan pencocokan sinyal garis jam. Kerugiane yaiku kapasitansi ing terminal sing cocog karo RC bisa mengaruhi bentuk lan kecepatan panyebaran sinyal kasebut.

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. Terminal pencocokan resistor seri uga duwe kauntungan kanggo nyuda jumlah piranti sing digunakake ing papan lan kerapatan koneksi.

The final method is to separate the matching terminal, in which the matching element needs to be placed near the receiving end. Keuntungane yaiku ora bakal narik sinyal, lan bisa dadi apik banget supaya ora rame. Biasane digunakake kanggo sinyal input 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.

Ing mode pemasangan vertikal, resistensi duwe pin sing dipasang cekak, sing nyuda resistensi termal ing antarane resistensi lan papan sirkuit lan nggawe panas resistensi luwih gampang dipancarake ing udhara. Nanging instalasi vertikal sing luwih dawa bakal nambah induktansi resistor. Instalasi horisontal duwe induktansi sing luwih murah amarga instalasi sing luwih murah. 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. Teknologi liyane sing ditrapake

Kanggo nyuda overshoot voltase sementara ing pasokan listrik IC, kapasitor decoupling kudu ditambahake ing chip IC. Iki kanthi efektif ngilangi pengaruh burrs ing pasokan listrik lan nyuda radiasi saka loop daya ing papan cetak.

Efek pelemburan burr paling apik nalika kapasitor decoupling disambungake langsung menyang sikil pasokan listrik sirkuit terintegrasi tinimbang lapisan pasokan listrik. Iki sebabe sawetara piranti duwe kapasitor decoupling ing kanthong, dene liyane mbutuhake jarak antarane kapasitor decoupling lan piranti kasebut cukup cilik.

Piranti konsumsi daya kanthi kecepatan dhuwur lan dhuwur kudu dilampirake nganti bisa nyuda voltase suplai listrik sing diluwari.

Tanpa lapisan listrik, garis listrik dawa nggawe loop ing antarane sinyal lan loop, dadi sumber radiasi lan sirkuit induktif.

Kabel mbentuk loop sing ora ngliwati kabel jaringan sing padha utawa kabel liyane diarani loop terbuka. Yen daur ulang liwat kabel jaringan sing padha, rute liyane nggawe loop tertutup. Ing kaloro kasus kasebut, efek antena (antena baris lan antena dering) bisa kedadeyan.