Sanoat, ilmiy va tibbiy radiochastotali (ISM-RF) mahsulotlarni qo’llashning ko’p holatlari shuni ko’rsatadiki bosilgan elektron karta Ushbu mahsulotlarning joylashuvi turli nuqsonlarga moyil.Odamlar tez -tez bir xil ICni ikki xil elektron platalarga o’rnatilishini aniqlaydilar, ishlash ko’rsatkichlari sezilarli darajada farq qiladi. Variations in operating conditions, harmonic radiation, anti-interference ability, and start-up time can explain the importance of circuit board layout in a successful design.

This article lists the various design omissions, discusses the causes of each failure, and provides suggestions on how to avoid these design defects. Ushbu maqolada, fr-4 dielektrik, qalinligi 0.0625 dyuymli ikki qavatli tenglikni, misol sifatida, elektron kartani erga ulash. Operating in different frequency bands between 315MHz and 915MHz, Tx and Rx power between -120dbm and +13dBm.

Induktivlik yo’nalishi

Agar ikkita induktor (yoki hatto ikkita tenglikni chizig’i) bir -biriga yaqin bo’lsa, o’zaro indüktans paydo bo’ladi. The magnetic field generated by the current in the first circuit excites the current in the second circuit (Figure 1). This process is similar to the interaction between the primary and secondary coils of a transformer. When two currents interact through a magnetic field, the voltage generated is determined by mutual inductance LM:

Bu erda, YB – B zanjiriga yuborilgan xato voltaji, IA – A zanjirida ishlaydigan 1 oqim. LM is very sensitive to circuit spacing, inductance loop area (i.e., magnetic flux), and loop direction. Therefore, the best balance between compact circuit layout and reduced coupling is the correct alignment of all inductors in the direction.

FIG. 1. It can be seen from magnetic field lines that mutual inductance is related to inductance alignment direction

The direction of circuit B is adjusted so that its current loop is parallel to the magnetic field line of circuit A. Shu maqsadda, iloji boricha bir -biriga perpendikulyar ravishda, kam quvvatli FSK superheterodinli qabul qiluvchilarni baholash (EV) platasining (MAX7042EVKIT) sxemasiga qarang (2 -rasm). The three inductors on the board (L3, L1 and L2) are very close to each other, and their orientation at 0°, 45° and 90° helps to reduce mutual inductance.

Shakl 2. Ikki xil PCB sxemasi ko’rsatilgan, ulardan birida elementlar noto’g’ri yo’nalishda joylashtirilgan (L1 va L3), ikkinchisi esa ko’proq mos keladi.

Xulosa qilib aytganda, quyidagi printsiplarga amal qilish kerak:

Endüktans oralig’i iloji boricha bo’lishi kerak.

Induktorlar orasidagi kesishishni minimallashtirish uchun induktor to’g’ri burchak ostida joylashtirilgan.

Kuplajni boshqaring

Induktorlarning yo’nalishi magnit birikmasiga qanday ta’sir qilsa, simlar bir -biriga juda yaqin bo’lsa, ulanish ham ta’sir qiladi. Bunday tartib muammosi o’zaro sezish deb ataladigan narsani ham keltirib chiqaradi. Chastotani chastotasi bilan bog’liq muammolardan biri bu tizimning sezgir qismlarini, masalan, kirish mos keladigan tarmoqni, qabul qiluvchining rezonansli kanalini, uzatgichning antennaga mos keluvchi tarmog’ini ulashdir.

Qaytish oqimi yo’li nurlanish magnit maydonini kamaytirish uchun imkon qadar asosiy oqimga yaqin bo’lishi kerak. This arrangement helps to reduce the current loop area. Qaytish oqimi uchun ideal past qarshilik yo’li, odatda, qo’rg’oshin ostidagi tuproqli erdir – bu halqa maydonini dielektrikning qalinligi qo’rg’oshin uzunligiga ko’paytiriladigan hudud bilan samarali cheklaydi. Ammo, agar er maydoni bo’linsa, pastadir maydoni oshadi (3 -rasm). For leads passing through the split region, the return current will be forced through the high resistance path, greatly increasing the current loop area. This arrangement also makes circuit leads more susceptible to mutual inductance.

Shakl 3. To’liq katta maydonli topraklama tizim ish faoliyatini yaxshilashga yordam beradi

Haqiqiy induktor uchun qo’rg’oshin yo’nalishi magnit maydonining ulanishiga ham katta ta’sir ko’rsatadi. Agar sezgir kontaktlarning zanglashiga olib keladigan simlari bir -biriga yaqin bo’lishi kerak bo’lsa, ulanishni kamaytirish uchun simlarni vertikal ravishda tekislash yaxshiroqdir (4 -rasm). If vertical alignment is not possible, consider using a guard line. Himoya simlarini loyihalash uchun quyidagi topraklama va to’ldirish ishlov berish bo’limiga qarang.

Figure 4. Similar to Figure 1, shows the possible coupling of magnetic field lines.

To sum up, the following principles should be followed when the plate is distributed:

Complete grounding should be ensured below the lead.

Sensitive leads should be arranged vertically.

If the leads must be arranged in parallel, ensure adequate spacing or use guard wires.

Grounding via

RF chastotasi sxemasining asosiy muammosi, odatda, kontaktlarning zanglashiga olib keladigan xarakterli impedansidir, shu jumladan, elektron komponentlari va ularning o’zaro bog’liqligi. Yupqa mis qoplamali qo’rg’oshin endüktans simiga teng va atrofdagi boshqa simlar bilan taqsimlangan sig’im hosil qiladi. Qo’rg’oshin, shuningdek, teshikdan o’tayotganda indüktans va sig’im xususiyatlarini ko’rsatadi.

The through-hole capacitance mainly comes from the capacitance formed between the copper cladding on the side of the through-hole pad and the copper cladding on the ground, separated by a fairly small ring. Another influence comes from the cylinder of the metal perforation itself. Parazitar sig’imning ta’siri odatda kichikdir va odatda yuqori tezlikdagi raqamli signallarning o’zgarishiga olib keladi (bu maqolada muhokama qilinmaydi).

Teshikning eng katta ta’siri mos keladigan o’zaro bog’lanish rejimidan kelib chiqqan parazitar induktivlikdir. Because most metal perforations in RF PCB designs are the same size as lumped components, the effect of electrical perforations can be estimated using a simple formula (FIG. 5) :

Where, LVIA is lumped inductance through hole; H is the height of the throughhole, in inches; D – teshikning diametri, dyuym 2.

Bosilgan taxtalarning PCB joylashuvidagi turli nuqsonlardan qanday qochish mumkin

FIG. 5. PCB cross section used to estimate parasitic effects on through-hole structures

The parasitic inductance often has a great influence on the connection of bypass capacitors. Ideal bypass kondansatörleri, besleme zonasi va qatlam o’rtasida yuqori chastotali qisqa tutashuvlarni ta’minlaydi, lekin ideal bo’lmagan teshiklar qatlam va ta’minot zonasi orasidagi past sezgirlik yo’liga ta’sir qilishi mumkin. A typical PCB through hole (d = 10 mil, h = 62.5 mil) is approximately equivalent to a 1.34nH inductor. ISM-RF mahsulotining o’ziga xos ish chastotasini hisobga olgan holda, teshiklar rezonansli kanallar, filtrlar va mos tarmoqlar kabi sezgir davrlarga salbiy ta’sir ko’rsatishi mumkin.

Agar sezgir davrlar, masalan, π tipidagi tarmoqning ikki qo’li, teshiklarni ulashsa, boshqa muammolar paydo bo’ladi. Masalan, biriktirilgan indüktansa teng bo’lgan ideal teshikni qo’yib, ekvivalent sxemasi sxemaning dastlabki dizaynidan ancha farq qiladi (6 -rasm). As with crosstalk of common current path 3, resulting in increased mutual inductance, increased crosstalk and feed-through.

How to avoid PCB design problems

Shakl 6. Ideal va ideal bo’lmagan arxitekturalar, sxemada potentsial “signal yo’llari” mavjud.

To sum up, circuit layout should follow the following principles:

Ensure modeling of through-hole inductance in sensitive areas.

The filter or matching network uses independent through-holes.

Note that a thinner PCB copper-clad will reduce the effect of parasitic inductance through the hole.

Qo’rg’oshinning uzunligi

Maxim ISM-RF mahsulot ma’lumotlari tez-tez yo’qotishlar va nurlanishni kamaytirish uchun yuqori chastotali kirish va chiqishning eng qisqa yo’llaridan foydalanishni tavsiya qiladi. Boshqa tomondan, bunday yo’qotishlar odatda ideal bo’lmagan parazitar parametrlar tufayli yuzaga keladi, shuning uchun ham parazitar indüktans ham, sig’im ham elektron sxemasiga ta’sir qiladi va eng qisqa simdan foydalanish parazitar parametrlarni kamaytirishga yordam beradi. Typically, a 10 mil wide PCB lead with a distance of 0.0625in… From a FR4 board produces an inductance of approximately 19nH/in and a distributed capacitance of approximately 1pF/in. 20nH induktorli va 3pF kondansatkichli LAN/ mikser sxemasi uchun kontaktlarning zanglashiga olib kelishi va komponentlarning joylashuvi juda ixcham bo’lganda, komponentlarning samarali qiymati katta ta’sir ko’rsatadi.

Ipc-d-317a4 in ‘Institute for Printed Circuits’ provides an industry standard equation for estimating various impedance parameters of microstrip PCB. Ushbu hujjat 2003 yilda IPC-2251 5 bilan almashtirildi, bu har xil PCB simlarini hisoblashning aniqroq usulini beradi. Online calculators are available from a variety of sources, most of which are based on equations provided by IPC-2251. The Electromagnetic Compatibility Lab at Missouri Institute of Technology provides a very practical method for calculating PCB lead impedance 6.

The accepted criteria for calculating the impedance of microstrip lines are:

Formulada εr – dielektrikning dielektrik konstantasi, h – qatlamdan qo’rg’oshinning balandligi, V – qo’rg’oshin kengligi, T – qo’rg’oshinning qalinligi (7 -rasm). Qachon soatiga 0.1 dan 2.0 gacha va r 1 dan 15 gacha bo’lsa, bu formulaning hisoblash natijalari juda aniq.

Figure 7. This figure is a PCB cross section (similar to Figure 5) and represents the structure used to calculate the impedance of a microstrip line.

In order to evaluate the effect of lead length, it is more practical to determine the detuning effect of ideal circuit by lead parasitical parameters. Bu misolda biz adashgan sig’im va indüktans haqida gaplashamiz. The standard equation of characteristic capacitance for microstrip lines is:

Xuddi shunday, xarakteristik induktivlikni yuqoridagi tenglama yordamida tenglamadan hisoblash mumkin:

Misol uchun, tenglikni qalinligi 0.0625in. (h = 62.5 mil), 1 untsiya mis bilan qoplangan qo’rg’oshin (t = 1.35 mil), 0.01in. (w = 10 mil) va FR-4 taxtasi. E’tibor bering, FR-4 ε R odatda 4.35 farad/m (F/m), lekin 4.0F/m dan 4.7F/m gacha bo’lishi mumkin. Bu misolda hisoblangan o’z qiymatlari Z0 = 134 ω, C0 = 1.04pF/in, L0 = 18.7nH/in.

AN ISM-RF konstruktsiyasi uchun bortdagi 12.7 mm (0.5 dyuym) simi uzunligi taxminan 0.5 pF va 9.3 nH parazitar parametrlarni ishlab chiqarishi mumkin (8-rasm). Bu darajadagi parazitar parametrlarning qabul qiluvchining rezonans kanaliga ta’siri (LC mahsulotining o’zgarishi) 315MGts ± 2% yoki 433.92mGts ± 3.5% o’zgarishiga olib kelishi mumkin. Qo’rg’oshinning parazitar ta’siridan kelib chiqadigan qo’shimcha sig’im va indüktans tufayli, 315 MGts tebranish chastotasining cho’qqisi 312.17 MGts ga, 433.92 MGts tebranish chastotasining cho’qqisi 426.6 MGts ga etadi.

Another example is the resonant channel of Maxim’s superheterodyne receiver (MAX7042). The recommended components are 1.2pF and 30nH at 315MHz; At 433.92MHz, it is 0pF and 16nH. Tenglama yordamida rezonansli davrning tebranish chastotasini hisoblang:

Plitaning rezonansli sxemasini baholash paket va parazit ta’sirini o’z ichiga olishi kerak va 7.3MGts rezonans chastotasini hisoblashda parazit parametrlari mos ravishda 7.5PF va 315PF bo’lishi kerak. E’tibor bering, LC mahsuloti yig’ilgan sig’imni ifodalaydi.

Xulosa qilib aytganda, quyidagi printsiplarga amal qilish kerak:

Etakchini iloji boricha qisqa tuting.

Kalit zanjirlarni qurilmaga iloji boricha yaqinroq joylashtiring.

Asosiy komponentlar haqiqiy parazitizmga muvofiq kompensatsiya qilinadi.

Topraklama va to’ldirish bilan ishlov berish

The grounding or power layer defines a common reference voltage that supplies power to all parts of the system through a low resistance path. Shunday qilib, barcha elektr maydonlarini tenglashtirish yaxshi himoya mexanizmini ishlab chiqaradi.

To’g’ridan -to’g’ri oqim har doim past qarshilik yo’li bilan oqadi. Xuddi shu tarzda, yuqori chastotali oqim, eng past qarshilikka ega bo’lgan yo’l orqali oqadi. So, for a standard PCB microstrip line above the formation, the return current tries to flow into the ground region directly below the lead. As described in the lead coupling section above, the cut ground area introduces various noises that increase crosstalk either through magnetic field coupling or by converging currents (Figure 9).

Bosilgan taxtalarning PCB joylashuvidagi turli nuqsonlardan qanday qochish mumkin

FIG. 9. Keep the formation intact as much as possible, otherwise the return current will cause crosstalk.

Filled ground, also known as guard lines, is commonly used in circuits where continuous grounding is difficult to lay or where shielding sensitive circuits is required (FIG. 10). The shielding effect can be increased by placing grounding holes (i.e. hole arrays) at both ends of the lead or along the lead. 8. Qaytish oqimini ta’minlash uchun mo’ljallangan himoya simini qo’rg’oshin bilan aralashtirmang. Bu tartib o’zaro bog’liqlikni keltirib chiqarishi mumkin.

Bosilgan taxtalarning PCB joylashuvidagi turli nuqsonlardan qanday qochish mumkin

ANJIR. 10. RF tizimining konstruktsiyasi suzuvchi mis qoplamali simlardan qochishi kerak, ayniqsa mis qoplamasi kerak bo’lsa.

Mis bilan qoplangan maydon faqat bir uchida topraklanmagan (suzuvchi) yoki erga ulanmagan, bu uning samaradorligini cheklaydi. In some cases, it can cause unwanted effects by forming parasitic capacitance that changes the impedance of the surrounding wiring or creates a “latent” path between circuits. Muxtasar qilib aytganda, izchil qoplama qalinligini ta’minlash uchun elektron plataga mis qoplamali bo’lak (uzluksiz signal simlari) qo’yilsa. Mis bilan qoplangan joylardan qochish kerak, chunki ular kontaktlarning zanglashiga ta’sir qiladi.

Nihoyat, antenna yaqinidagi har qanday er maydonining ta’sirini hisobga olishni unutmang. Har qanday monopol antennada tizim muvozanatining bir qismi sifatida tuproqli hudud, simlar va teshiklar bo’ladi, va ideal bo’lmagan muvozanatli simlar antennaning nurlanish samaradorligi va yo’nalishiga ta’sir qiladi (radiatsion shablon). Therefore, the ground area should not be placed directly below the monopole PCB lead antenna.

Xulosa qilib aytganda, quyidagi printsiplarga amal qilish kerak:

Iloji boricha doimiy va past qarshilikli topraklama zonalarini ta’minlang.

To’ldirish chizig’ining ikkala uchi topraklanmış va iloji boricha teshikli qator ishlatiladi.

Mis qoplamali simni RF zanjiri yaqinida suzib yurmang, RF zanjiri atrofida mis yotqizmang.

Agar elektron kartada bir nechta qatlam bo’lsa, signal kabeli bir tomondan ikkinchisiga o’tganda, teshik orqali er qo’yish yaxshidir.

Haddan tashqari kristalli sig’im

Parasitic capacitance will cause the crystal frequency to deviate from the target value 9. Shu sababli, kristalli pinlar, prokladkalar, simlar yoki RF qurilmalariga ulanishning adashgan sig’imini kamaytirish uchun ba’zi umumiy ko’rsatmalarga amal qilish kerak.

The following principles should be followed:

Kristal va RF qurilmasi orasidagi aloqa imkon qadar qisqa bo’lishi kerak.

Iloji boricha simlarni bir -biridan uzoqroq tuting.

Agar shunt parazitar sig’imi juda katta bo’lsa, kristal ostidagi topraklama qismini olib tashlang.

Planar simlarning indüktivligi

Planar wiring or PCB spiral inductors are not recommended. Typical PCB manufacturing processes have certain inaccuracies, such as width and space tolerances, which greatly affect the accuracy of component values. Shuning uchun, nazorat qilinadigan va yuqori Q induktorlarining ko’pchiligi yara turiga kiradi. Ikkinchidan, siz ko’p qatlamli keramik induktorni tanlashingiz mumkin, ko’p qatlamli chip kondansatör ishlab chiqaruvchilari ham ushbu mahsulotni taqdim etadilar. Shunga qaramay, ba’zi dizaynerlar kerak bo’lganda spiral induktorlarni tanlaydilar. The standard formula for calculating planar spiral inductance is usually Wheeler’s formula 10:

Bu erda, a – lasanning o’rtacha radiusi, dyuymda; N – burilishlar soni; C-lasan yadrosining kengligi (router-rinner), dyuymda. Qachon bobin c “0.2a 11, hisoblash usuli aniqligi 5%ichida.

Kvadrat, olti burchakli yoki boshqa shaklli bir qatlamli spiral induktorlardan foydalanish mumkin. Integral elektronli plastinalarda tekislik indüktansını modellashtirish uchun juda yaxshi taxminlarni topish mumkin. Bu maqsadga erishish uchun standart Wheeler formulasi kichik o’lchamli va 12 kvadrat kattalik uchun mos keladigan tekislik indüktans baholash usulini olish uchun o’zgartiriladi.

Bu erda, ρ – to’ldirish nisbati :; N – burilishlar soni, va dAVG – o’rtacha diametri:. Kvadrat spirallar uchun K1 = 2.36, K2 = 2.75.

Ushbu turdagi induktorni ishlatmaslik uchun ko’p sabablar bor, bu odatda bo’shliq cheklovlari tufayli indüktans qiymatlarining pasayishiga olib keladi. The main reasons for avoiding planar inductors are limited geometry and poor control of critical dimensions, which makes it impossible to predict inductor values. Bundan tashqari, PCB ishlab chiqarish paytida haqiqiy indüktans qiymatlarini nazorat qilish qiyin, va indüktans shuningdek, kontaktlarning zanglashiga olib keladigan boshqa qismlariga ham shovqin qo’shadi.