Amatyala amaninzi ezicelo zeemveliso zenzululwazi, kunye nezonyango (ISM-RF) zibonisa ukuba ibhodi yesekethe eprintiweyo ubume bezi mveliso zihlala zithambekele kwiziphene ezahlukeneyo.Abantu bahlala befumanisa ukuba i-IC efanayo ifakwe kwiibhodi ezimbini ezahlukeneyo zesekethe, izikhombisi zentsebenzo ziya kwahluka kakhulu. 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. Kweli phepha, fr-4 dielectric, 0.0625in ubukhulu kabini umaleko PCB njengomzekelo, ibhodi yesekethe kumhlaba. Operating in different frequency bands between 315MHz and 915MHz, Tx and Rx power between -120dbm and +13dBm.

Ulwalathiso inductance

Xa ii-inductors ezimbini (okanye imigca emibini ye-PCB) zikufutshane enye kwenye, ukungenelela ngokufanayo kuya kwenzeka. 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:

Apho, i-YB yimpazamo yevolthi efakwe kwisekethe B, i-IA yeyoku-1 yangoku esebenza kwisekethe A. I-LM inovakalelo kakhulu kwisithuba seesekethe, indawo ye-inductance loop (okt, ukuhamba kwemagnethi), kunye nomkhombandlela we-loop. 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. Ukulungiselela le njongo, ngokungangqinelaniyo kangangoko kunokwenzeka komnye nomnye, nceda ujonge ubeko lwesekethe yamandla asezantsi e-FSK superheterodyne Receiver Evaluation (EV) board (MAX7042EVKIT) (Umzobo 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.

Umzobo 2. Ubeko ezimbini zePCB zibonisiwe, enye yazo inezinto ezilungiselelwe kwicala elingalunganga (i-L1 kunye ne-L3), ngelixa enye ifanelekile.

Ukushwankathela, le migaqo ilandelayo kufuneka ilandelwe:

Isithuba se-inductance kufuneka sibe kangangoko kunokwenzeka.

Abaqhubi bahlelwe kwii-angles ezilungileyo ukunciphisa i-crosstalk phakathi kwabangenisi.

Khokela ukudibanisa

Kanye njengokuqhelaniswa ne-inductors kuchaphazela ukuhlangana kwemagnethi, ngokunjalo nokudibanisa ukuba izikhokelo zisondele kakhulu komnye komnye. Olu hlobo lwengxaki luyila kwakhona into ebizwa ngokuba yimvakalelo efanayo. Enye yeengxaki ezixhalabisayo zesekethe ye-RF kukucwangciswa kwamalungu abuthathaka kwenkqubo, njengothungelwano lokuthelekisa, ishaneli somthamo somamkeli, inethiwekhi ehambelana ne-eriyali yomthumeli, njl.

Indlela ebuyayo yangoku kufuneka ikufutshane nomendo wangoku ongundoqo wokunciphisa umtsalane wombane. This arrangement helps to reduce the current loop area. Indlela efanelekileyo yokuxhathisa ukubuyela ngoku ihlala ingumhlaba ongaphantsi kokhokelo-ngokukunciphisa umda womda kummandla apho ubukhulu be-dielectric iphindaphindwe ngobude bokhokelo. Nangona kunjalo, ukuba indawo yomhlaba yahlulwe, indawo yeluphu iyanda (Umzobo 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.

Umzobo 3. Zalisa indawo enkulu yokuncothula umhlaba kunceda ukuphucula ukusebenza kwenkqubo

Yeyona inductor yokwenyani, isikhokelo esikhokelayo sikwanefuthe elibonakalayo kwindibaniselwano yentsimi yemagneti. Ukuba izikhokelo zesekethe ethe-ethe kufuneka zisondelane, kungcono ukulungelelanisa izikhokelo ngokuthe nkqo ukunciphisa ukudityaniswa (Umzobo 4). If vertical alignment is not possible, consider using a guard line. Kuyilo locingo lokhuselo, nceda ujonge kumhlaba wokwenza umhlaba kunye nokuzalisa unyango apha ngezantsi.

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

Eyona ngxaki iphambili kulwakhiwo lwesekethe yeRF ihlala ingumlinganiso ophantsi wendlela yesekethe, kubandakanya izinto zesekethe kunye nokunxibelelana kwazo. Isikhokelo esinokutyabeka ubhedu obhityileyo silingana nocingo lokungenisa kwaye senza amandla asasazwayo kunye nezinye izikhokelo kufutshane. Isikhokelo sikwabonisa ukunganyanzeliswa kunye neepropathi zokuhamba njengoko kudlula emngxunyeni.

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. Iziphumo ze-parasitic capacitance zihlala zincinci kwaye zihlala zibangela umahluko kumda wesantya esineempawu zedijithali (ezingakhankanywanga kweli phepha).

Iziphumo ezinkulu zokungena emngxunyeni kukunyanzeliswa kwe-parasitic okubangelwa yimowudi yokunxibelelana ehambelanayo. 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 bububanzi be -holehole, nge-intshi 2.

Indlela ukunqanda iziphene ezahlukeneyo kuyilo PCB iibhodi eziprintiweyo

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. I-capacitors yokugqitha efanelekileyo inikezela ngeesekethe ezihamba rhoqo eziphakathi phakathi kwendawo yokubonelela kunye nokwenziwa, kodwa ukungalunganga kwemingxunya kunokuchaphazela indlela ephantsi yokuziva uphakathi kolwakhiwo kunye nendawo yonikezelo. A typical PCB through hole (d = 10 mil, h = 62.5 mil) is approximately equivalent to a 1.34nH inductor. Ngenxa yokuhamba rhoqo kwemveliso ye-ISM-RF, imingxunya enokuthi ichaphazele imijikelezo ebuthathaka enje ngeesekethe zesanti ezinamathambo, izihluzi kunye nothungelwano olufanayo.

Ezinye iingxaki ziyavela ukuba iisekethe ezibuthathaka zabelana ngemingxunya, ezinje ngeengalo ezimbini zenethiwekhi yohlobo lwe-π. Umzekelo, ngokubeka umngxunya ofanelekileyo olinganiswe ne-lumped inductance, iskimu esilinganayo sahlukile kuyilo lokuqala lweesekethe (umzobo 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

Umzobo 6. Ucoceko ngokuchasene nolwakhiwo olungalunganga, zinokubakho “iindlela zomqondiso” kwisekethe.

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.

Ubude belothe

Idatha yemveliso ephezulu kakhulu ye-ISM-RF ihlala icebisa ukuba kusetyenziswe eyona ndlela imfutshane yokufaka isantya esiphezulu kunye nemveliso kukhokelela ekunciphiseni ilahleko kunye nemitha. Kwelinye icala, iilahleko ezinje zihlala zibangelwa ziiparasitic parameter ezingekho mgangathweni, ke ngoko zombini indasenti yokuqina kunye namandla okuchaphazela ubume besekethe, kwaye ukusebenzisa eyona mfutshane kunokwenzeka kukhokelela ekunciphiseni iiparameter. 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. Kwisekethe yeLAN / yomxhubi ene-20nH inductor kunye ne-3pF capacitor, ixabiso elisebenzayo lexabiso liya kuchaphazeleka kakhulu xa isekethe kunye nolwakhiwo lwecandelo zihambelana kakhulu.

Ipc-d-317a4 in ‘Institute for Printed Circuits’ provides an industry standard equation for estimating various impedance parameters of microstrip PCB. Olu xwebhu lwathatyathwa ngo-2003 yi-IPC-2251 5, ebonelela ngendlela echanekileyo yokubala kwizikhokelo ezahlukeneyo ze-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:

Kwifomyula, εr kukuqhubeka kwe-dielectric rhoqo, h ukuphakama kokukhokelela ukusuka kumtya, W bububanzi bokukhokela, kunye no-T ubukhulu bokukhokela (UMZEKELO 7). Xa i-w / h iphakathi kwe-0.1 kunye ne-2.0 kunye ne-εr iphakathi kwe-1 kunye ne-15, iziphumo zokubala zale fomyula zichanekile.

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. Kulo mzekelo, sixoxa ngobuchule obulahlekileyo kunye nokunyanzeliswa. The standard equation of characteristic capacitance for microstrip lines is:

Kwangokunjalo, uphawu lokunyanzeliswa lunokubalwa ukusuka kwi-equation ngokusebenzisa le nxaki ingentla:

Umzekelo, cinga i-PCB ubukhulu be-0.0625in. (h = 62.5 mil), i-ounce enye ekhokele ubhedu (t = 1 mil), 1.35in. (w = 0.01 mil), kunye nebhodi ye-FR-10. Qaphela ukuba i-ε R ye-FR-4 idla ngokuba yi-4.35 farad / m (F / m), kodwa inokubakho ukusuka kwi-4.0F / m ukuya kwi-4.7F / m. Iimpawu zendalo ezibalwe kulo mzekelo zi Z0 = 134 ω, C0 = 1.04pF / in, L0 = 18.7nH / in.

Uyilo lwe-ISM-RF, ubude be-12.7mm (0.5in) yobude bokukhokela ebhodini bunokuvelisa iiparasitic parameter ezimalunga ne-0.5pF kunye ne-9.3nH (Umzobo 8). Iziphumo zeparasitic parameter kweli nqanaba kwisitishi se-resonant (ukwahluka kwemveliso ye-LC) kunokubangela i-315MHz ± 2% okanye i-433.92mhz ± 3.5% yantlukwano. Ngenxa ye-capacitance eyongezelelweyo kunye ne-inductance ebangelwe sisiphumo se-parasitic yesikhokelo, incopho ye-315MHz oscillation frequency ifikelela kwi-312.17mhz, kwaye incopho ye-433.92mhz ye-oscillation frequency ifikelela kwi-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. Bala ukubakho kwamaza oscillation wesekethe evuthayo ngokusebenzisa i-equation:

Ukuvavanywa kwesekethe enesitayile setafile kufuneka kubandakanye ifuthe lesiphako sepakethe kunye nolwakhiwo, kunye neparasitic parameter yi-7.3PF kunye ne-7.5PF ngokwahlukeneyo xa kubalwa i-315MHz yokuphindaphindeka kwamaza. Qaphela ukuba imveliso ye-LC imele amandla e-lumped.

Ukushwankathela, le migaqo ilandelayo kufuneka ilandelwe:

Gcina ukukhokela kufutshane ngangokunokwenzeka.

Beka iisekethe eziphambili kufutshane nesixhobo kangangoko kunokwenzeka.

Izinto eziphambili ziyahlawulwa ngokungqinelana nobume beparasism.

Isiseko kunye nokuzalisa unyango

The grounding or power layer defines a common reference voltage that supplies power to all parts of the system through a low resistance path. Ukulinganisa onke amabala ombane ngale ndlela kuvelisa indlela efanelekileyo yokukhusela.

Okwangoku ngokuthe ngqo kuhlala kuthambekela kwindlela yokuxhathisa esezantsi. Ngendlela efanayo, ubukhulu becala obukhoyo ngoku ngokukhethekileyo buhamba ngendlela kunye noxhathiso olusezantsi. 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).

Indlela ukunqanda iziphene ezahlukeneyo kuyilo PCB iibhodi eziprintiweyo

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. Sukuxuba ucingo lokugada kunye nokhokelo olwenzelwe ukubuyisela indlela yangoku yokubuyela. Eli lungiselelo linokuzisa i-crosstalk.

Indlela ukunqanda iziphene ezahlukeneyo kuyilo PCB iibhodi eziprintiweyo

IKHIWANE. 10. Uyilo lwenkqubo yeRF kufuneka luthintele iingcingo ezilaliweyo zobhedu, ingakumbi ukuba kufanelekile ukwenza sheathing yobhedu.

Indawo enxibe ubhedu ayisekelwanga kumhlaba (edadayo) okanye ayimiswanga kwicala elinye kuphela, ethintela ukusebenza kwayo ngokufanelekileyo. 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. Ngamafutshane, ukuba isiqwenga sobhedu sobhedu (esingasiyiyo isekethe se-wiring) sibekwa kwibhodi yesekethe ukuqinisekisa ukungqinelana kwesingxobo. Iindawo ezinxibe ubhedu kufuneka zithintelwe njengoko zichaphazela uyilo lweesekethe.

Okokugqibela, qiniseka ukuba ujonge iziphumo zayo nayiphi na indawo yomhlaba kufutshane ne-eriyali. Nayiphi na i-eriyali ye-monopole iya kuba nomhlaba womhlaba, iintambo kunye nemingxunya njengenxalenye yenkqubo yokulingana, kunye nokungabikho kokulungelelanisa ii-wiring kuya kuchaphazela ukusebenza kakuhle kwemitha kunye nolwalathiso lwe-eriyali (itemplate yemitha). Therefore, the ground area should not be placed directly below the monopole PCB lead antenna.

Ukushwankathela, le migaqo ilandelayo kufuneka ilandelwe:

Ukubonelela ngokuqhubekayo kunye nokunciphisa ukuxhathisa imimandla ngokukhawuleza.

Zombini iziphelo zomgca wokugcwalisa zibekiwe, kwaye uluhlu olunemingxunya lusetyenziswa kangangoko kunokwenzeka.

Sukuntywila ucingo lwesixokelelwano sobhedu kufutshane ne-RF, ungabeki ubhedu ujikeleze isekethe yeRF.

Ukuba ibhodi yesekethe iqulethe iindawo ezininzi, kungcono ukubeka umhlaba ngomngxuma xa intambo yesiginali idlula kwelinye icala iye kwelinye.

Ukugqithisa okunyanzelekileyo kwekristale

Amandla e-parasitic capacitance aya kubangela ukuba i-crystal frequency iphambuke kwixabiso ekujoliswe kulo 9. Ke ngoko, ezinye izikhokelo ngokubanzi kufuneka zilandelwe ukunciphisa ukubhabha kwezikhonkwane zekristale, iiphedi, iingcingo, okanye unxibelelwano kwizixhobo zeRF.

Le migaqo ilandelayo kufuneka ilandelwe:

Unxibelelwano phakathi kwesixhobo se-crystal kunye ne-RF kufuneka lube lufutshane ngangokunokwenzeka.

Gcina i-wiring isuka komnye nomnye kangangoko kunokwenzeka.

Ukuba amandla e-parasitic parasitic capacitance makhulu kakhulu, susa indawo engaphantsi kwekristale.

Ukucwangciswa kwe-wiring inductance

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. Ke ngoko, uninzi lolawulo oluphezulu kunye noluphakamileyo lwe-Q luhlobo lwenxeba. Okwesibini, unokukhetha i-multilayer ceramic inductor, abavelisi bee-multilayer chip capacitor bakwabonelela ngale mveliso. Nangona kunjalo, abanye abayili bakhetha ukungena ngaphakathi xa kufuneka. The standard formula for calculating planar spiral inductance is usually Wheeler’s formula 10:

Apho, i-radius yomyinge wekhoyili, ngo-intshi; N linani lokujika; C bububanzi bekhoyili (riner-rinner), nge-intshi. Xa i-coil c “0.2a 11, ukuchaneka kwendlela yokubala ikwi-5%.

Maleko maleko olunye inductors isikwere, ezinamacala, okanye ezinye iimilo ingasetyenziswa. Ukulinganisa okuhle kakhulu kunokufunyanwa kwimodeli yokunyanzeliswa kwesicwangciso kwii-wafers zesekethe ezihlanganisiweyo. Ukufezekisa le njongo, ifomula esemgangathweni ye-Wheeler iguqulwe ukuze ifumane indlela yokuqikelela inductance efanelekileyo kubukhulu obuncinci kunye nobukhulu besikwere 12.

Phi, ρ ngumlinganiselo wokugcwalisa :; N linani lokujika, kwaye i-dAVG bububanzi obuphakathi:. Kwiikwere zeesikwere, K1 = 2.36, K2 = 2.75.

Zininzi izizathu zokuphepha ukusebenzisa olu hlobo lwe-inductor, oluhlala lukhokelela ekunciphiseni amaxabiso okunyanzeliswa ngenxa yesithintelo sendawo. The main reasons for avoiding planar inductors are limited geometry and poor control of critical dimensions, which makes it impossible to predict inductor values. Ukongeza, amaxabiso okwenyani kunzima ukulawula ngexesha lokuveliswa kwePCB, kwaye ukunganyanzeliswa kukwafuna ukubangaba yingxolo kwezinye iindawo zesekethe.