Bosta każijiet ta ‘applikazzjoni ta’ prodotti ta ‘frekwenza tar-radju industrijali, xjentifiċi u mediċi (ISM-RF) juru li l- b’ċirkwit stampat it-tqassim ta ‘dawn il-prodotti huwa suxxettibbli għal difetti varji.In-nies spiss isibu li l-istess IC installat fuq żewġ bordijiet ta ‘ċirkwiti differenti, l-indikaturi tal-prestazzjoni jkunu differenti b’mod sinifikanti. 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. F’din il-karta, fr-4 dielettriku, PCB ta ‘saff doppju ta’ ħxuna ta ‘0.0625in bħala eżempju, l-ert taċ-ċirkwit. Operating in different frequency bands between 315MHz and 915MHz, Tx and Rx power between -120dbm and +13dBm.

Direzzjoni ta ‘induttanza

Meta żewġ indutturi (jew saħansitra żewġ linji tal-PCB) ikunu viċin xulxin, induttanza reċiproka sseħħ. 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:

Fejn, YB huwa l-vultaġġ ta ‘żball injettat fiċ-ċirkwit B, IA huwa l-kurrent 1 li jaġixxi fuq iċ-ċirkwit A. 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. Għal dan il-għan, kemm jista ‘jkun perpendikulari għal xulxin, jekk jogħġbok irreferi għat-tqassim taċ-ċirkwit tal-bord ta’ Evalwazzjoni tar-Riċevitur (EV) superheterodyne ta ‘enerġija baxxa (MAX7042EVKIT) (Figura 2). 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.

Figura 2. Żewġ tqassim differenti tal-PCB huma murija, li wieħed minnhom għandu l-elementi rranġati fid-direzzjoni ħażina (L1 u L3), filwaqt li l-ieħor huwa aktar adattat.

Fil-qosor, għandhom jiġu segwiti l-prinċipji li ġejjin:

L-ispazjar tal-inductance għandu jkun kemm jista ‘jkun possibbli.

L-indutturi huma rranġati f’angoli retti biex jimminimizzaw il-krosstalk bejn l-indutturi.

Imexxi l-igganċjar

Hekk kif l-orjentazzjoni ta ‘l-indutturi taffettwa l-igganċjar manjetiku, hekk ukoll l-igganċjar jekk il-wajers huma viċin wisq ta’ xulxin. Dan it-tip ta ‘problema ta’ tqassim jipproduċi wkoll dik li tissejjaħ sensazzjoni reċiproka. Waħda mill-aktar problemi kkonċernati taċ-ċirkwit RF hija l-wajers ta ‘partijiet sensittivi tas-sistema, bħan-netwerk li jaqbel ma’ l-input, kanal reżonanti tar-riċevitur, netwerk li jaqbel ma ‘l-antenna tat-trasmettitur, eċċ.

Il-passaġġ tal-kurrent ta ‘ritorn għandu jkun viċin il-passaġġ tal-kurrent ewlieni kemm jista’ jkun biex jimminimizza l-kamp manjetiku tar-radjazzjoni. This arrangement helps to reduce the current loop area. Il-mogħdija ta ‘reżistenza baxxa ideali għall-kurrent ta’ ritorn hija ġeneralment ir-reġjun ta ‘l-art taħt iċ-ċomb – effettivament tillimita ż-żona tal-linja għal reġjun fejn il-ħxuna tad-dielettriku hija mmultiplikata bit-tul taċ-ċomb. Madankollu, jekk ir-reġjun tal-art jinqasam, iż-żona tal-linja tiżdied (Figura 3). 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.

Figura 3. L-ert komplut ta ‘erja kbira jgħin biex itejjeb il-prestazzjoni tas-sistema

Għal induttur attwali, id-direzzjoni taċ-ċomb għandha wkoll effett sinifikanti fuq l-akkoppjar tal-kamp manjetiku. Jekk iċ-ċombi ta ‘ċirkwit sensittiv għandhom ikunu viċin xulxin, l-aħjar huwa li tallinja l-wajers vertikalment biex tnaqqas l-igganċjar (Figura 4). If vertical alignment is not possible, consider using a guard line. Għad-disinn tal-wajer ta ‘protezzjoni, jekk jogħġbok irreferi għat-taqsima tat-trattament tal-ert u tal-mili hawn taħt.

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

Il-problema ewlenija bit-tqassim taċ-ċirkwit RF hija ġeneralment l-impedenza karatteristika subottimali taċ-ċirkwit, inklużi l-komponenti taċ-ċirkwit u l-interkonnessjonijiet tagħhom. Iċ-ċomb b’kisja rqiqa tar-ram huwa ekwivalenti għall-wajer ta ‘l-induttanza u jifforma kapaċitanza distribwita ma’ wajers oħra fil-viċinanza. Iċ-ċomb juri wkoll proprjetajiet ta ’inductance u capacitance hekk kif jgħaddi mit-toqba.

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. L-effett tal-kapaċitanza parassita ġeneralment huwa żgħir u ġeneralment jikkawża biss varjazzjoni fit-tarf f’sinjali diġitali b’veloċità għolja (li mhix diskussa f’dan id-dokument).

L-akbar effett tat-toqba li tgħaddi huwa l-induttanza parassita kkawżata mill-mod ta ‘interkonnessjoni korrispondenti. 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 huwa d-dijametru tat-toqba ta ‘ġewwa, f’pulzieri 2.

Kif tevita diversi difetti fit-tqassim tal-PCB tal-bordijiet stampati

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. Kondensers tal-bypass ideali jipprovdu ċirkuwiti qosra ta ‘frekwenza għolja bejn iż-żona tal-provvista u l-formazzjoni, iżda toqob li mhumiex ideali jistgħu jaffettwaw il-passaġġ ta’ sensittività baxxa bejn il-formazzjoni u ż-żona tal-provvista. A typical PCB through hole (d = 10 mil, h = 62.5 mil) is approximately equivalent to a 1.34nH inductor. Minħabba l-frekwenza operattiva speċifika tal-prodott ISM-RF, it-toqob li jgħaddu jistgħu jaffettwaw ħażin ċirkuwiti sensittivi bħal ċirkwiti ta ‘kanali reżonanti, filtri, u netwerks li jaqblu.

Problemi oħra jinqalgħu jekk ċirkwiti sensittivi jaqsmu toqob, bħaż-żewġ fergħat ta ‘netwerk tat-tip π. Pereżempju, billi tpoġġi toqba ideali ekwivalenti għal inductance f’daqqa, l-iskematiku ekwivalenti huwa pjuttost differenti mid-disinn taċ-ċirkwit oriġinali (FIG. 6). As with crosstalk of common current path 3, resulting in increased mutual inductance, increased crosstalk and feed-through.

How to avoid PCB design problems

Figura 6. Ideali kontra arkitetturi mhux ideali, hemm “mogħdijiet tas-sinjali” potenzjali fiċ-ċirkwit.

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.

It-tul taċ-ċomb

Id-dejta tal-prodott Maxim ISM-RF ħafna drabi tirrakkomanda l-użu tal-iqsar frekwenza għolja possibbli li twassal għal input u output biex tnaqqas it-telf u r-radjazzjoni. Min-naħa l-oħra, telf bħal dan ġeneralment ikun ikkawżat minn parametri parassitiċi mhux ideali, għalhekk kemm l-induttanza parassita kif ukoll il-kapaċitanza jaffettwaw it-tqassim taċ-ċirkwit, u l-użu tal-iqsar ċomb possibbli jgħin biex jitnaqqsu l-parametri parassitiċi. 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. Għal ċirkwit LAN / mixer b’induttur ta ’20nH u kapaċitatur 3pF, il-valur tal-komponent effettiv jiġi affettwat ħafna meta ċ-ċirkwit u t-tqassim tal-komponent ikunu kompatti ħafna.

Ipc-d-317a4 in ‘Institute for Printed Circuits’ provides an industry standard equation for estimating various impedance parameters of microstrip PCB. Dan id-dokument ġie sostitwit fl-2003 minn IPC-2251 5, li jipprovdi metodu ta ‘kalkolu aktar preċiż għal diversi wajers tal-PCB. 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:

Fil-formula, εr hija l-kostanti dielettrika tad-dielettriku, h huwa l-għoli taċ-ċomb mill-istratum, W hija l-wisa ‘taċ-ċomb, u T hija l-ħxuna taċ-ċomb (FIG. 7). Meta w / h huwa bejn 0.1 u 2.0 u εr huwa bejn 1 u 15, ir-riżultati tal-kalkolu ta ‘din il-formula huma pjuttost preċiżi.

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. F’dan l-eżempju, niddiskutu kapaċitanza u induttanza mitlufa. The standard equation of characteristic capacitance for microstrip lines is:

Bl-istess mod, l-induttanza karatteristika tista ‘tiġi kkalkulata mill-ekwazzjoni billi tuża l-ekwazzjoni ta’ hawn fuq:

Pereżempju, assumi ħxuna tal-PCB ta ‘0.0625in. (h = 62.5 mil), 1 uqija taċ-ċomb miksi bir-ram (t = 1.35 mil), 0.01in. (w = 10 mil), u bord FR-4. Innota li l-ε R ta ‘FR-4 hija tipikament 4.35 farad / m (F / m), iżda tista’ tvarja minn 4.0F / m sa 4.7F / m. L-eigenvalues ​​ikkalkulati f’dan l-eżempju huma Z0 = 134 ω, C0 = 1.04pF / in, L0 = 18.7nH / in.

Għal disinn ISM-RF, tul ta ‘tqassim ta’ 12.7mm (0.5in) taċ-ċomb fuq il-bord jista ‘jipproduċi parametri parassiti ta’ madwar 0.5pF u 9.3nH (Figura 8). L-effett tal-parametri parassitiċi f’dan il-livell fuq il-kanal reżonanti tar-riċevitur (varjazzjoni tal-prodott LC) jista ‘jirriżulta f’varjazzjoni ta’ 315MHz ± 2% jew 433.92mhz ± 3.5%. Minħabba l-kapaċitanza u l-induttanza addizzjonali kkawżati mill-effett parassitiku taċ-ċomb, il-quċċata tal-frekwenza ta ‘oxxillazzjoni 315MHz tilħaq 312.17mhz, u l-quċċata tal-frekwenza ta’ oxxillazzjoni 433.92mhz tilħaq 426.6mhz.

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. Ikkalkula l-frekwenza tal-oxxillazzjoni taċ-ċirkwit reżonanti billi tuża l-ekwazzjoni:

L-evalwazzjoni taċ-ċirkwit reżonanti tal-pjanċa għandha tinkludi l-effetti parassitiċi tal-pakkett u t-tqassim, u l-parametri parassiti huma 7.3PF u 7.5PF rispettivament meta tiġi kkalkulata l-frekwenza reżonanti 315MHz. Innota li l-prodott LC jirrappreżenta kapaċitanza f’daqqa.

Fil-qosor, għandhom jiġu segwiti l-prinċipji li ġejjin:

Żomm iċ-ċomb qasir kemm jista ‘jkun.

Poġġi ċirkwiti ewlenin kemm jista ‘jkun viċin l-apparat.

Il-komponenti ewlenin huma kkumpensati skont il-parassitiżmu tat-tqassim attwali.

Trattament għall-ert u mili

The grounding or power layer defines a common reference voltage that supplies power to all parts of the system through a low resistance path. L-ugwaljanza tal-kampijiet elettriċi kollha b’dan il-mod tipproduċi mekkaniżmu tajjeb ta ‘lqugħ.

Il-kurrent dirett dejjem għandu t-tendenza li jiċċirkola tul mogħdija ta ‘reżistenza baxxa. Bl-istess mod, kurrent ta ‘frekwenza għolja preferibbilment jgħaddi mill-passaġġ bl-inqas reżistenza. 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).

Kif tevita diversi difetti fit-tqassim tal-PCB tal-bordijiet stampati

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. Tħallatx il-wajer ta ‘lqugħ maċ-ċomb iddisinjat biex jipprovdi mogħdija ta’ kurrent ta ‘ritorn. Dan l-arranġament jista ‘jintroduċi krosstalk.

Kif tevita diversi difetti fit-tqassim tal-PCB tal-bordijiet stampati

FIG. 10. Id-disinn tas-sistema RF għandu jevita wajers miksi tar-ram li jżommu f’wiċċ l-ilma, speċjalment jekk tkun meħtieġa kisi tar-ram.

Iż-żona miksija bir-ram mhijiex ertjata (f’wiċċ l-ilma) jew ertjata biss f’tarf wieħed, li tirrestrinġi l-effettività tagħha. 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. Fil-qosor, jekk biċċa kisi tar-ram (wajers tas-sinjal mhux taċ-ċirkwit) titqiegħed fuq il-bord taċ-ċirkwit biex tkun żgurata ħxuna konsistenti tal-kisi. Żoni miksi bir-ram għandhom jiġu evitati billi jaffettwaw id-disinn taċ-ċirkwit.

Fl-aħħarnett, kun żgur li tikkunsidra l-effetti ta ‘kwalunkwe żona ta’ l-art ħdejn l-antenna. Kwalunkwe antenna monopole jkollha r-reġjun tal-art, wajers u toqob bħala parti mill-ekwilibriju tas-sistema, u wajers ta ‘ekwilibriju mhux ideali jaffettwaw l-effiċjenza tar-radjazzjoni u d-direzzjoni tal-antenna (mudell tar-radjazzjoni). Therefore, the ground area should not be placed directly below the monopole PCB lead antenna.

Fil-qosor, għandhom jiġu segwiti l-prinċipji li ġejjin:

Ipprovdi żoni ta ‘ert kontinwi u ta’ reżistenza baxxa kemm jista ‘jkun.

Iż-żewġt itruf tal-linja tal-mili huma msejsa fuq l-art, u firxa ta ‘toqob li jintużaw kemm jista’ jkun.

Tagħmilx fil-wiċċ wajer miksi bir-ram ħdejn ċirkwit RF, tpoġġix ram madwar ċirkwit RF.

Jekk il-bord taċ-ċirkwit fih saffi multipli, l-aħjar huwa li tqiegħed art minn toqba meta l-kejbil tas-sinjal jgħaddi minn naħa għall-oħra.

Kapaċitanza tal-kristall eċċessiva

Parasitic capacitance will cause the crystal frequency to deviate from the target value 9. Għalhekk, għandhom jiġu segwiti xi linji gwida ġenerali biex titnaqqas il-kapaċitanza mitlufa ta ‘labar tal-kristall, pads, wajers, jew konnessjonijiet ma’ apparat RF.

The following principles should be followed:

Il-konnessjoni bejn il-kristall u l-apparat RF għandha tkun qasira kemm jista ‘jkun.

Keep the wiring from each other as far as possible.

Jekk il-kapaċitanza parassita tax-shunt hija kbira wisq, neħħi r-reġjun tal-ert taħt il-kristall.

Induttanza tal-wajers ċatti

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. Għalhekk, l-iktar indutturi Q ikkontrollati u għoljin huma tat-tip tal-ferita. It-tieni, tista ‘tagħżel induttur taċ-ċeramika b’ħafna saffi, il-manifatturi tal-kapaċitaturi taċ-ċippa b’ħafna saffi jipprovdu wkoll dan il-prodott. Madankollu, xi disinjaturi jagħżlu indutturi spirali meta jkollhom. The standard formula for calculating planar spiral inductance is usually Wheeler’s formula 10:

Fejn, a huwa r-raġġ medju tal-koljatura, f’pulzieri; N huwa n-numru ta ‘dawriet; C hija l-wisa ‘tal-qalba tal-coil (router-rinner), f’pulzieri. Meta l-coil c “0.2a 11, l-eżattezza tal-metodu tal-kalkolu hija fi ħdan 5%.

Jistgħu jintużaw indutturi spirali ta ‘saff wieħed ta’ forom kwadri, eżagonali, jew forom oħra. Jistgħu jinstabu approssimazzjonijiet tajbin ħafna biex jimmudellaw l-induttanza ċatta fuq wejfers taċ-ċirkwit integrat. Sabiex jintlaħaq dan il-għan, il-formula standard ta ‘Wheeler hija modifikata biex jinkiseb metodu ta’ stima ta ‘induttanza tal-pjan adattat għal daqs żgħir u daqs kwadru 12.

Fejn, ρ huwa l-proporzjon tal-mili :; N huwa n-numru ta ‘dawriet, u dAVG huwa d-dijametru medju:. Għal eliċi kwadri, K1 = 2.36, K2 = 2.75.

Hemm ħafna raġunijiet biex tevita li tuża dan it-tip ta ‘induttur, li ġeneralment jirriżultaw f’valuri ta’ induttanza mnaqqsa minħabba limitazzjonijiet ta ‘spazju. The main reasons for avoiding planar inductors are limited geometry and poor control of critical dimensions, which makes it impossible to predict inductor values. Barra minn hekk, il-valuri attwali tal-induttanza huma diffiċli biex jiġu kkontrollati waqt il-produzzjoni tal-PCB, u l-induttanza għandha wkoll it-tendenza li tgħaqqad l-istorbju ma ‘partijiet oħra taċ-ċirkwit.