Integral kontaktlarning zanglashiga olib o’tish tezligining oshishi bilan PCB kartasi density, Signal Integrity has become one of the issues that must be concerned in high-speed digital PCB design. The parameters of components and PCB board, the layout of components on PCB board, the wiring of high-speed Signal line and other factors, Can cause problems with signal integrity.

For PCB layouts, signal integrity requires a board layout that does not affect signal timing or voltage, while for circuit wiring, signal integrity requires termination elements, layout strategies, and wiring information. PCBda yuqori signal tezligi, oxirgi komponentlarning noto’g’ri joylashuvi yoki yuqori tezlikdagi signallarning noto’g’ri ulanishi signalning yaxlitligi bilan bog’liq muammolarni keltirib chiqarishi mumkin, bu tizimning noto’g’ri ma’lumot chiqarishi, kontaktlarning zanglashiga olib kelishi yoki umuman ishlamasligi mumkin. How to take signal integrity into full consideration and take effective control measures in PCB design has become a hot topic in PCB design industry.

Signal integrity Problem Good signal integrity means that the signal can respond with the correct timing and voltage level values when required. Aksincha, signal to’g’ri javob bermasa, signal yaxlitligi muammosi paydo bo’ladi. Signalning yaxlitligi muammolari signalning buzilishiga, vaqt xatolariga, noto’g’ri ma’lumotlar, manzil va nazorat liniyalariga, tizimning noto’g’ri ishlashiga yoki hatto tizimning ishdan chiqishiga olib kelishi mumkin. PCB dizayni amaliyotida odamlar PCB dizayn qoidalarini ko’p to’pladilar. PCB dizaynida, ushbu dizayn qoidalariga diqqat bilan murojaat qilish orqali tenglikni uzatishning yaxlitligiga yaxshiroq erishish mumkin.

When designing PCB, we should first understand the design information of the whole circuit board, which mainly includes:

1. The number of devices, device size, device package, chip rate, whether PCB is divided into low speed, medium speed and high speed area, which is the interface input and output area;

2. The overall layout requirements, device layout location, whether there is a high power device, chip device heat dissipation special requirements;

3. Signal liniyasining turi, tezligi va uzatish yo’nalishi, signal liniyasining impedans nazorati talablari, avtobus tezligi yo’nalishi va haydash holati, asosiy signallar va himoya choralari;

4. Elektr ta’minoti turi, erning turi, elektr ta’minoti va erga nisbatan shovqinlarga chidamlilik talablari, elektr ta’minoti va er tekisligining sozlanishi va segmentatsiyasi;

5. Soat chiziqlarining turlari va stavkalari, soat yo’nalishlarining manbasi va yo’nalishi, soatni kechiktirish talablari, eng uzun chiziqli talablar.

PCB qatlamli dizayni

Elektron kartaning asosiy ma’lumotlarini tushunganingizdan so’ng, elektron kartochkaning dizayn talablari va signallarning yaxlitligini o’lchash va simi qatlamlarining oqilona sonini tanlash kerak. At present, the circuit board has gradually developed from single layer, double layer and four layer to more multi-layer circuit board. Multi-layer PCB design can improve the reference surface of signal routing and provide backflow path for signal, which is the main measure to achieve good signal integrity. When designing PCB layering, follow the following rules:

1. Malumot tekisligi tercihen er tekisligi bo’lishi kerak. Both power supply and ground plane can be used as reference plane, and both have certain shielding function. Shu bilan birga, elektr ta’minoti tekisligining himoya ta’siri yer tekisligiga qaraganda ancha past bo’ladi, chunki uning xarakteristikasi yuqori empedans va quvvat manbai tekisligi va mos yozuvlar zamin darajasi o’rtasidagi katta potentsial farq.

2. Digital circuit and analog circuit are layered. Dizayn xarajatlari ruxsat etilgan joylarda raqamli va analogli sxemalarni alohida qatlamlarda joylashtirish yaxshidir. If must want to arrange in same wiring layer, can use ditch, add earthing line, the method such as dividing line to remedy. Analog va raqamli quvvat va tuproqni ajratish kerak, hech qachon aralashtirmang.

3. Qo’shni qatlamlarning asosiy signal yo’nalishi segmentatsiya maydonini kesib o’tmaydi. Signallar butun mintaqada katta signal uzukini hosil qiladi va kuchli nurlanish hosil qiladi. If the signal cable must cross the area when the ground cable is divided, a single point can be connected between the ground to form a connection bridge between the two ground points, and then the cable can be routed through the connection bridge.

4. Komponent yuzasi ostida nisbatan to’liq zamin tekisligi bo’lishi kerak. Ko’p qatlamli plastinka uchun zamin tekisligining yaxlitligi imkon qadar saqlanishi kerak. Hech qanday signal liniyalari odatda yer tekisligida ishlashiga yo’l qo’yilmaydi.

5, yuqori chastotali, yuqori tezlikli, soatli va boshqa kalit signal chiziqlari ulashgan er tekisligiga ega bo’lishi kerak. In this way, the distance between signal line and ground line is only the distance between PCB layers, so the actual current always flows in the ground line directly below the signal line, forming the smallest signal loop area and reducing radiation.

How to design the signal of integrity PCB

PCB layout design

Bosilgan taxtaning signal yaxlitligi dizaynining kaliti bu PCB ishlashiga bevosita bog’liq bo’lgan tartib va ​​simlardir. Prior to layout, the PCB size must be determined to meet the function at the lowest possible cost. Agar PCB juda katta va taqsimlangan bo’lsa, uzatish liniyasi juda uzun bo’lishi mumkin, buning natijasida impedans kuchayadi, shovqin qarshiligi pasayadi va narx oshadi. Agar komponentlar bir -biriga joylashtirilsa, issiqlik tarqalishi yomon bo’ladi va ulashgan simlarda o’zaro bog’liqlik paydo bo’lishi mumkin. Shuning uchun, sxema elektromagnit moslashuv, issiqlik tarqalishi va interfeys omillarini hisobga olgan holda, sxemaning funktsional birliklariga asoslangan bo’lishi kerak.

Aralash raqamli va analog signallari bo’lgan tenglikni yotqizayotganda raqamli va analog signallarni aralashtirmang. Agar analog va raqamli signallarni aralashtirish kerak bo’lsa, o’zaro bog’lanish ta’sirini kamaytirish uchun vertikal chiziq qo’yishni unutmang. Elektron platadagi raqamli kontaktlarning zanglashiga olib keladigan, analogli va shovqin chiqaruvchi elektronni ajratish kerak, birinchi navbatda sezgir kontaktlarning zanglashiga olib borish va kontaktlarning zanglashiga olib keladigan yo’lni yo’q qilish kerak. Xususan, soatni, qayta tiklash va uzilish liniyalarini ko’rib chiqing, bu chiziqlarni yuqori tok o’tkazgich liniyalariga parallel qilmang, aks holda elektromagnit ulash signallari bilan osonlikcha shikastlanib, kutilmagan qayta o’rnatish yoki uzilishga olib keladi. The overall layout should follow the following principles:

1. Funktsional bo’lim tartibi, analog elektron va PCBdagi raqamli elektronlar har xil fazoviy joylashuvga ega bo’lishi kerak.

2. O’chirish signallari jarayoniga ko’ra, funktsional elektron birliklarni tartibga solish, shu bilan signal oqimi bir xil yo’nalishni saqlab turishi uchun.

3. Take the core components of each functional circuit unit as the center, and other components are arranged around it.

4. Shorten the connection between high-frequency components as much as possible and try to reduce their distribution parameters.

5. Oson bezovtalanuvchi komponentlar bir-biriga juda yaqin bo’lmasligi kerak, kirish va chiqish komponentlari uzoqda bo’lishi kerak.

How to design the signal of integrity PCB

PCB simlari dizayni

Barcha signal liniyalari tenglikni simlarini ulashdan oldin tasniflanishi kerak. First of all, clock line, sensitive signal line, and then high-speed signal line, in order to ensure that this kind of signal through the hole is enough, distribution parameters of good characteristics, and then general unimportant signal line.

Incompatible signal lines should be far away from each other and do not parallel wiring, such as digital and analog, high speed and low speed, high current and small current, high voltage and low voltage. Kesishishni kamaytirish uchun turli qatlamlardagi signal kabellari vertikal ravishda bir -biriga yo’naltirilishi kerak. Signal liniyalarining joylashuvi signalning oqim yo’nalishiga ko’ra yaxshiroq joylashtirilgan. Devrenning chiqish signal chizig’i kirish signali liniyasi maydoniga qaytarilmasligi kerak. High-speed signal lines should be kept as short as possible to avoid interfering with other signal lines. Ikkita panelda, agar kerak bo’lsa, yuqori tezlikdagi signal chizig’ining har ikki tomoniga izolyatsion topraklama simini qo’shish mumkin. Ko’p qatlamli taxtadagi barcha yuqori tezlikdagi soat chiziqlari soat chiziqlarining uzunligiga qarab himoyalangan bo’lishi kerak.

Ulanishning umumiy printsiplari:

1. Iloji boricha past zichlikdagi simli konstruksiyani va signal simlarini iloji boricha qalinlikka mos keladigan, impedansga mos keladigan tarzda tanlash. RF sxemasi uchun signal chizig’ining yo’nalishi, kengligi va chiziq oralig’ining asossiz dizayni signal uzatish liniyalari o’rtasida o’zaro aralashuvga olib kelishi mumkin.

2. Iloji boricha qo’shni kirish va chiqish simlari va uzoq masofali parallel simlardan qochish uchun. Parallel signal liniyalarining kesishishini kamaytirish uchun signal liniyalari orasidagi masofani oshirish yoki signal chiziqlari orasiga izolyatsiya kamarlarini kiritish mumkin.

3. PCBdagi chiziq kengligi bir xil bo’lishi kerak va chiziq kengligi mutatsiyasiga yo’l qo’yilmaydi. PCB simining egilishi 90 daraja burchakdan foydalanmasligi kerak, chiziq empedansining uzluksizligini saqlab qolish uchun iloji boricha yoy yoki 135 daraja burchakdan foydalanish kerak.

4. Minimize the area of the current loop. The external radiation intensity of current-carrying circuit is proportional to the current passing through, the loop area and the square of signal frequency. Reducing the current loop area can reduce the ELECTROMAGNETIC interference of PCB.

5. Iloji boricha simning uzunligini qisqartirish, simning kengligini oshirish, simning impedansini kamaytirishga yordam beradi.

6. Kommutatorni boshqarish signallari uchun bir vaqtning o’zida holatini o’zgartiradigan SIGNAL PCB simlarining soni iloji boricha kamaytirilishi kerak.