Kesi nyingi za matumizi ya bidhaa za redio za viwanda, kisayansi, na matibabu (ISM-RF) zinaonyesha kuwa printed mzunguko bodi mpangilio wa bidhaa hizi unakabiliwa na kasoro anuwai.Mara nyingi watu hugundua kuwa IC hiyo hiyo imewekwa kwenye bodi mbili za mzunguko tofauti, viashiria vya utendaji vitakuwa tofauti sana. 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. Katika karatasi hii, fr-4 dielectric, 0.0625in unene safu mbili za PCB kama mfano, bodi ya mzunguko ikituliza. Operating in different frequency bands between 315MHz and 915MHz, Tx and Rx power between -120dbm and +13dBm.

Mwelekeo wa kushawishi

Wakati inductors mbili (au hata mistari miwili ya PCB) ziko karibu na kila mmoja, inductance ya pande zote itatokea. 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:

Ambapo, YB ni voltage ya kosa iliyoingizwa kwenye mzunguko B, IA ndio 1 ya sasa inayofanya kazi kwenye mzunguko 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. Kwa kusudi hili, kwa kadiri iwezekanavyo kwa kila mmoja, tafadhali rejelea mpangilio wa mzunguko wa bodi ya chini ya nguvu ya FSK superheterodyne Revenue Tathmini (EV) (MAX7042EVKIT) (Kielelezo 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.

Kielelezo 2. Mipangilio miwili tofauti ya PCB imeonyeshwa, moja ambayo ina vitu vilivyopangwa kwa mwelekeo usiofaa (L1 na L3), wakati nyingine inafaa zaidi.

Kwa muhtasari, kanuni zifuatazo zinapaswa kufuatwa:

Nafasi ya inductance inapaswa kuwa iwezekanavyo.

Wafanyabiashara hupangwa kwa pembe za kulia ili kupunguza msalaba kati ya waendeshaji.

Kiongozi kuunganishwa

Kama vile mwelekeo wa inductors huathiri uunganishaji wa sumaku, ndivyo uunganishaji ikiwa viongozo viko karibu sana kwa kila mmoja. Aina hii ya shida ya mpangilio pia hutoa kile kinachoitwa hisia za pande zote. Shida moja inayojali sana ya mzunguko wa RF ni wiring ya sehemu nyeti za mfumo, kama mtandao wa vinavyolingana na pembejeo, kituo cha resonant cha mpokeaji, mtandao unaolingana wa antena ya mpitishaji, nk.

Njia ya sasa ya kurudi inapaswa kuwa karibu na njia kuu ya sasa iwezekanavyo ili kupunguza uwanja wa sumaku ya mionzi. This arrangement helps to reduce the current loop area. Njia bora ya upinzani wa chini kwa sasa ya kurudi kawaida ni eneo la ardhini chini ya risasi – inapunguza kabisa eneo la kitanzi kwa mkoa ambapo unene wa dielectri huzidishwa na urefu wa risasi. Walakini, ikiwa eneo la ardhi limegawanyika, eneo la kitanzi linaongezeka (Kielelezo 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.

Picha 3. Kukamilisha kutuliza eneo kubwa husaidia kuboresha utendaji wa mfumo

Kwa inductor halisi, mwelekeo wa risasi pia una athari kubwa kwenye unganisho la uwanja wa sumaku. Ikiwa mwongozo wa mzunguko nyeti lazima uwe karibu na kila mmoja, ni bora kulinganisha viongozo kwa wima ili kupunguza kuunganisha (Kielelezo 4). If vertical alignment is not possible, consider using a guard line. Kwa muundo wa waya wa ulinzi, tafadhali rejea sehemu ya kutuliza na kujaza matibabu hapa chini.

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

Shida kuu na mpangilio wa mzunguko wa RF kawaida ni hali ndogo ya tabia ya mzunguko, pamoja na vifaa vya mzunguko na unganisho lao. Kuongoza na mipako nyembamba ya shaba ni sawa na waya wa inductance na hufanya uwezo wa kusambazwa na vielelezo vingine katika maeneo ya karibu. Kiongozi pia huonyesha sifa za kufata na uwezo wakati inapita kwenye shimo.

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. Athari za uwezo wa vimelea kwa ujumla ni ndogo na kawaida husababisha tu tofauti za makali katika ishara za dijiti za kasi (ambazo hazijadiliwi kwenye jarida hili).

Athari kubwa ya shimo la kupitisha ni uingizaji wa vimelea unaosababishwa na hali inayolingana ya unganisho. 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 ni kipenyo cha shimo, katika inchi 2.

Jinsi ya kuzuia kasoro anuwai katika mpangilio wa PCB wa bodi zilizochapishwa

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. Viboreshaji bora vya kupitisha hutoa mizunguko fupi ya masafa ya juu kati ya eneo la ugavi na malezi, lakini mashimo yasiyofaa kupitia mashimo yanaweza kuathiri njia ya unyeti wa chini kati ya malezi na eneo la usambazaji. A typical PCB through hole (d = 10 mil, h = 62.5 mil) is approximately equivalent to a 1.34nH inductor. Kutokana na mzunguko maalum wa uendeshaji wa bidhaa ya ISM-RF, mashimo ya kupitia yanaweza kuathiri vibaya nyaya nyeti kama vile nyaya za resonant, vichungi na mitandao inayofanana.

Shida zingine huibuka ikiwa mizunguko nyeti inashiriki mashimo, kama mikono miwili ya mtandao wa aina ya π. Kwa mfano, kwa kuweka shimo bora sawa na inductance ya lumped, schematic sawa ni tofauti kabisa na muundo wa mzunguko wa asili (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

Kielelezo 6. Usanifu bora dhidi ya usanifu usiofaa, kuna uwezekano wa “njia za ishara” katika mzunguko.

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.

Urefu wa risasi

Takwimu za bidhaa za Maxim ISM-RF mara nyingi hupendekeza kutumia pembejeo fupi na masafa mafupi iwezekanavyo na pato husababisha kupunguza hasara na mionzi. Kwa upande mwingine, hasara kama hizo kawaida husababishwa na vigezo visivyo bora vya vimelea, kwa hivyo inductance ya vimelea na uwezo huathiri mpangilio wa mzunguko, na kutumia risasi fupi inayowezekana husaidia kupunguza vigezo vya vimelea. 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. Kwa mzunguko wa LAN / mixer na inductor ya 20nH na 3pF capacitor, thamani ya sehemu inayofaa itaathiriwa sana wakati mzunguko na mpangilio wa sehemu ni ngumu sana.

Ipc-d-317a4 in ‘Institute for Printed Circuits’ provides an industry standard equation for estimating various impedance parameters of microstrip PCB. Hati hii ilibadilishwa mnamo 2003 na IPC-2251 5, ambayo inatoa njia sahihi zaidi ya hesabu kwa miongozo anuwai ya 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:

Katika fomula, εr ni dielectri ya kila mara ya dielectri, h ni urefu wa risasi kutoka kwa safu, W ni upana wa risasi, na T ni unene wa risasi (FIG. 7). Wakati w / h ni kati ya 0.1 na 2.0 na εr ni kati ya 1 na 15, matokeo ya hesabu ya fomula hii ni sahihi kabisa.

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. Katika mfano huu, tunajadili uwezo wa kupotea na inductance. The standard equation of characteristic capacitance for microstrip lines is:

Vivyo hivyo, inductance ya tabia inaweza kuhesabiwa kutoka kwa equation kwa kutumia equation hapo juu:

Kwa mfano, fikiria unene wa PCB wa 0.0625in. (h = mil 62.5), ounce 1 risasi iliyofunikwa na shaba (t = 1.35 mil), 0.01in. (w = mil 10), na bodi ya FR-4. Kumbuka kuwa ε R ya FR-4 kawaida ni 4.35 farad / m (F / m), lakini inaweza kutoka 4.0F / m hadi 4.7F / m. Vipimo vilivyohesabiwa katika mfano huu ni Z0 = 134 ω, C0 = 1.04pF / in, L0 = 18.7nH / in.

Kwa muundo wa AN ISM-RF, urefu wa mpangilio wa 12.7mm (0.5in) wa risasi kwenye bodi inaweza kutoa vigezo vya vimelea vya takriban 0.5pF na 9.3nH (Kielelezo 8). Athari za vigezo vya vimelea katika kiwango hiki kwenye kituo cha resonant cha mpokeaji (tofauti ya bidhaa ya LC) inaweza kusababisha 315MHz ± 2% au 433.92mhz ± 3.5% tofauti. Kwa sababu ya uwezo wa ziada na upunguzaji unaosababishwa na athari ya vimelea ya risasi, kilele cha mzunguko wa oscillation wa 315MHz hufikia 312.17mhz, na kilele cha mzunguko wa oscillation wa 433.92mhz hufikia 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. Mahesabu ya mzunguko wa oscillation wa mzunguko wa resonant kwa kutumia equation:

Tathmini ya mzunguko wa bamba inapaswa kujumuisha athari za vimelea za kifurushi na mpangilio, na vigezo vya vimelea ni 7.3PF na 7.5PF mtawaliwa wakati wa kuhesabu masafa ya 315MHz ya resonant. Kumbuka kuwa bidhaa ya LC inawakilisha uwezo wa lumped.

Kwa muhtasari, kanuni zifuatazo lazima zifuatwe:

Endelea kuongoza kwa ufupi iwezekanavyo.

Weka mizunguko muhimu karibu na kifaa iwezekanavyo.

Vipengele muhimu hulipwa kulingana na muundo halisi wa vimelea.

Kutuliza na kujaza matibabu

The grounding or power layer defines a common reference voltage that supplies power to all parts of the system through a low resistance path. Kulinganisha uwanja wote wa umeme kwa njia hii hutoa utaratibu mzuri wa kukinga.

Sasa ya moja kwa moja huwa inapita katikati ya njia ya chini ya upinzani. Kwa njia hiyo hiyo, hali ya juu-frequency ya sasa inapita kwa njia na upinzani wa chini kabisa. 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).

Jinsi ya kuzuia kasoro anuwai katika mpangilio wa PCB wa bodi zilizochapishwa

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. Usichanganye waya wa walinzi na risasi iliyoundwa ili kutoa njia ya kurudi ya sasa. Mpangilio huu unaweza kuanzisha crosstalk.

Jinsi ya kuzuia kasoro anuwai katika mpangilio wa PCB wa bodi zilizochapishwa

MFANO. 10. Muundo wa mfumo wa RF unapaswa kuepuka waya zilizofungwa za shaba, haswa ikiwa kukatwa kwa shaba kunahitajika.

Eneo lililofunikwa kwa shaba halina msingi (kuelea) au msingi tu kwa ncha moja, ambayo inazuia ufanisi wake. 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. Kwa kifupi, ikiwa kipande cha kufunika shaba (wiring isiyo ya mzunguko) imewekwa kwenye bodi ya mzunguko ili kuhakikisha unene thabiti wa mchovyo. Maeneo yaliyofunikwa kwa shaba yanapaswa kuepukwa kwani yanaathiri muundo wa mzunguko.

Mwishowe, hakikisha kuzingatia athari za eneo lolote la ardhi karibu na antena. Antena yoyote ya monopole itakuwa na eneo la chini, wiring na mashimo kama sehemu ya usawa wa mfumo, na wiring isiyo sawa ya usawa itaathiri ufanisi wa mionzi na mwelekeo wa antena (template ya mionzi). Therefore, the ground area should not be placed directly below the monopole PCB lead antenna.

Kwa muhtasari, kanuni zifuatazo zinapaswa kufuatwa:

Kutoa maeneo ya kutuliza na kuendelea na upinzani mdogo iwezekanavyo.

Mwisho wote wa mstari wa kujaza umewekwa chini, na safu ya shimo hutumiwa kwa kadri iwezekanavyo.

Usitie waya iliyofungwa ya shaba karibu na mzunguko wa RF, usiweke shaba kuzunguka mzunguko wa RF.

Ikiwa bodi ya mzunguko ina tabaka nyingi, ni bora kuweka ardhi kupitia shimo wakati kebo ya ishara inapita kutoka upande mmoja hadi mwingine.

Uwezo mkubwa wa kioo

Parasitic capacitance will cause the crystal frequency to deviate from the target value 9. Kwa hivyo, miongozo mingine ya jumla inapaswa kufuatwa ili kupunguza uwezo wa kupotea wa pini za kioo, pedi, waya, au unganisho kwa vifaa vya RF.

Kanuni zifuatazo zinapaswa kufuatwa:

Uunganisho kati ya kioo na kifaa cha RF inapaswa kuwa fupi iwezekanavyo.

Weka wiring kutoka kwa kila mmoja iwezekanavyo.

Ikiwa uwezo wa vimelea wa shunt ni kubwa sana, ondoa eneo la kutuliza chini ya kioo.

Uingizaji wa wiring wa sayari

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. Kwa hivyo, inductors zinazodhibitiwa na za juu za Q ni aina ya jeraha. Pili, unaweza kuchagua inductor multilayer kauri, wazalishaji wa chip multilayer chip pia hutoa bidhaa hii. Walakini, wabunifu wengine huchagua waingizaji wa ond wakati lazima. The standard formula for calculating planar spiral inductance is usually Wheeler’s formula 10:

Ambapo, a ni eneo la wastani la coil, kwa inchi; N ni idadi ya zamu; C ni upana wa msingi wa coil (router-rinner), kwa inchi. Wakati coil c “0.2a 11, usahihi wa njia ya hesabu iko ndani ya 5%.

Vipande vyenye safu moja ya mraba, hexagonal, au maumbo mengine yanaweza kutumika. Makadirio mazuri sana yanaweza kupatikana kwa mfano wa upangaji wa mpango kwenye kaki za mzunguko zilizounganishwa. Ili kufikia lengo hili, fomula ya kawaida ya Wheeler imebadilishwa ili kupata njia ya kukadiria inductance inayofaa kwa saizi ndogo na saizi ya mraba 12.

Wapi, ρ ni uwiano wa kujaza :; N ni idadi ya zamu, na dAVG ni kipenyo cha wastani:. Kwa helices za mraba, K1 = 2.36, K2 = 2.75.

Kuna sababu nyingi za kuzuia kutumia aina hii ya inductor, ambayo kawaida husababisha kupunguzwa kwa maadili ya sababu ya upungufu wa nafasi. The main reasons for avoiding planar inductors are limited geometry and poor control of critical dimensions, which makes it impossible to predict inductor values. Kwa kuongeza, maadili halisi ya inductance ni ngumu kudhibiti wakati wa uzalishaji wa PCB, na inductance pia huwa na kelele kadhaa kwa sehemu zingine za mzunguko.