Kuyilo lwe Ibhodi PCB, kunye nokwanda ngokukhawuleza kwamaxesha, kuya kubakho ukuphazamiseka okuninzi okwahlukileyo kwibhodi ye-PCB ephantsi. Ngaphezu koko, kunye nokwanda amaza kunye nokungqubana phakathi miniaturization kunye neendleko eziphantsi ibhodi PCB, ezi ukuphazamiseka kuya kusiba nzima ngakumbi.

Kuphando lokwenyani, sinokugqiba ukuba kukho izinto ezine zokuphazamiseka, kubandakanya ingxolo yombane, ukuphazamiseka komgca wokuhambisa, ukudibanisa nokuphazamiseka kwe-electromagnetic (EMI). Ngokuhlalutya iingxaki ezahlukeneyo zokungena kwi-PCB ephezulu kunye nokudibanisa nokusebenza emsebenzini, izisombululo ezisebenzayo zibekwa phambili.

Okokuqala, ingxolo yombane

Kwisekethe ephezulu yokujikeleza, ingxolo yonikezelo lwamandla inefuthe elicacileyo kumqondiso wokuhamba rhoqo. Therefore, the first requirement of the power supply is low noise. Clean floors are just as important as clean electricity. Why? The power characteristics are shown in Figure 1. Ngokucacileyo, umbane une-impedance ethile, kwaye i-impedance ihanjiswa ngaphezulu kombane wonke, ke ngoko, ingxolo iya kongezwa kunikezelo lwamandla.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Kuyilo lwesekethe ye-hf, kungcono ngakumbi ukuyila unikezelo lwamandla njengobungqingili kunebhasi kwiimeko ezininzi, ukuze iluphu ihlale ilandela umendo we-impedance encinci.

In addition, the power board must provide a signal loop for all generated and received signals on the PCB. This minimizes the signal loop and thus reduces noise, which is often overlooked by low-frequency circuit designers.

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Umzobo 1: Iimpawu zamandla

Kukho iindlela ezininzi zokuphelisa ingxolo yamandla kuyilo lwePCB:

1. Note the through hole on the board: the through hole requires etched openings on the power supply layer to leave space for the through hole to pass through. If the opening of the power supply layer is too large, it is bound to affect the signal loop, the signal is forced to bypass, the loop area increases, and the noise increases. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Jonga umzobo 2.

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Umzobo 2: Indlela eqhelekileyo yokudlula kwilogo yomqondiso

2. The connection line needs enough ground: each signal needs to have its own proprietary signal loop, and the loop area of the signal and loop is as small as possible, that is to say, the signal and loop should be parallel.

3. Ukunikezelwa kwamandla e-Analog kunye nedijithali ukwahlula: izixhobo ezinamaza aphezulu zihlala zibuthathaka kwingxolo yedijithali, ke ezi zimbini kufuneka zahlulwe, zidityaniswe kunye ekungeneni kombane, ukuba umqondiso kwi-analog nakwiindawo zedijithali ze amagama, anokubekwa kumqondiso ukunqumla kwiluphu ukunciphisa indawo yeluphu. Ubungakanani be-digital-analog esetyenziselwa ilogo yomqondiso ibonisiwe kuMzobo 3.

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Figure 3: Digital – analog span for signal loop

4. Avoid overlapping of separate power supplies between layers: otherwise circuit noise can easily pass through parasitic capacitive coupling.

5. Isolate sensitive components: such as PLL.

6. Place the power cable: To reduce the signal loop, place the power cable on the edge of the signal line to reduce the noise, as shown in Figure 4.

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Umzobo 4: Beka intambo yombane ecaleni komgca wesiginali

Two, transmission line

Zimbini kuphela iindlela zokudlulisela kwi-PCB:

Ingxaki enkulu kumgca webhebhoni kunye nomgca we-microwave ubonakalisa. Ukucamngca kuya kubangela iingxaki ezininzi. Umzekelo, isiginali yomthwalo iya kuba kukuphakanyiswa kwesiginali yentsusa kunye nomqondiso we-echo, oya kuthi wandise ubunzima bohlalutyo lwesiginali. Ukucamngca kubangela ilahleko ebuyayo (ukubuya kwelahleko), echaphazela uphawu ngokungalunganga njengokuphazamiseka kwengxolo eyongeziweyo:

1. Isiginali ebonakaliswe umva kumthombo wophawu iyakwandisa ingxolo yenkqubo, yenze kube nzima ngakumbi kumamkeli ukwahlula ingxolo kumqondiso;

2. Any reflected signal will basically degrade the signal quality and change the shape of the input signal. Generally speaking, the solution is mainly impedance matching (for example, the impedance of the interconnection should very match the impedance of the system), but sometimes the calculation of impedance is more troublesome, you can refer to some transmission line impedance calculation software. The methods of eliminating transmission line interference in PCB design are as follows:

(a) Avoid impedance discontinuity of transmission lines. Inqaku lokuyekiswa kwe-impedance yindawo yokuhambisa utshintsho kumgca, njengokungena ngqo kwikona, ngomngxunya, njl. Njl., Kufuneka kuthintelwe kangangoko kunokwenzeka. Iindlela: Ukuthintela iikona ezichanekileyo zomgca, ukuya kuthi ga kwi-45 ° i-Angle okanye i-arc, i-Angle enkulu inokuba nayo; Use as few through holes as possible, because each through hole is an impedance discontinuity, as shown in FIG. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

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Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Kuba nayiphi na ingqumba yomnatha ingumthombo wengxolo. Ukuba umgca we-pile mfutshane, unokudibaniswa ekupheleni komgca wokuhambisa; Ukuba umgca we-pile mde, uya kuthatha umgca wokuhambisa ophambili njengomthombo kwaye uvelise ukubonakaliswa okukhulu, okuya kwenza ingxaki kube nzima. Kuyacetyiswa ukuba ungayisebenzisi.

Okwesithathu, ukudibanisa

1. Common impedance coupling: it is a common coupling channel, that is, the interference source and the interfered device often share some conductors (such as loop power supply, bus, and common grounding), as shown in Figure 6.

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Umzobo 6: Ukuhlangana kwe-impedance eqhelekileyo

In this channel, the drop back of the Ic causes a common-mode voltage in the series current loop, affecting the receiver.

2. The field common-mode coupling will cause the radiation source to cause common-mode voltages in the loop formed by the interfered circuit and on the common reference surface.

If the magnetic field is dominant, the value of the common-mode voltage generated in the series ground circuit is Vcm=-(△B/△t)* area (where △B= change in magnetic induction intensity). If it is an electromagnetic field, when its electric field value is known, its induced voltage: Vcm=(L* H *F*E)/48, the formula is suitable for L(m)=150MHz, beyond this limit, the calculation of the maximum induced voltage can be simplified as: Vcm=2* H *E.

3. Differential mode field coupling: refers to the direct radiation by wire pair or circuit board on the lead and its loop induction received. If you get as close to the two wires as possible. Oku kudityaniswa kuncitshiswe kakhulu, ke iingcingo zombini zinokujijisana kunye ukunciphisa uphazamiseko.

4. Inter-line coupling (crosstalk) can cause unwanted coupling between any line or parallel circuit, which will greatly damage the performance of the system. Its type can be divided into capacitive crosstalk and perceptual crosstalk.

The former is because the parasitic capacitance between the lines makes the noise on the noise source coupled to the noise receiving line through current injection. The latter can be thought of as the coupling of signals between the primary stages of an unwanted parasitic transformer. Ubungakanani be-crosstalk e-inductive ixhomekeke kufutshane kwezi khonkco zimbini, ubungakanani bendawo yeluphu, kunye nokuphazamiseka komthwalo ochaphazelekayo.

5. Ukudityaniswa kwentambo yamandla: Iiakethi zombane ze-ac okanye ze-DC ziphazanyiswa kukuphazamiseka kwe-electromagnetic

Transfer to other devices.

There are several ways to eliminate crosstalk in PCB design:

1. Both types of crosstalk increase with the increase of load impedance, so the signal lines sensitive to interference caused by crosstalk should be properly terminated.

2. Khulisa umgama phakathi kwemigca yesiginali ukunciphisa ngokufanelekileyo i-capacitive crosstalk. Ulawulo lomhlaba, isithuba phakathi kweentambo (ezinje ngemigca yesiginali esebenzayo kunye nemigca yomhlaba yokuzihlukanisa, ngakumbi kwimeko yokutsiba phakathi komgca wesiginali kunye nomhlaba ukuya kwisithuba) kunye nokunciphisa ukungafakwanga.

3. Capacitive crosstalk can also be effectively reduced by inserting a ground wire between adjacent signal lines, which must be connected to the formation every quarter of a wavelength.

4. Nge-crosstalk enengqiqo, indawo yeluphu kufuneka incitshiswe, kwaye ukuba kuvunyelwe, iluphu kufuneka isuswe.

5. Avoid signal sharing loops.

6. Nika ingqalelo kwingqibelelo yomqondiso: umyili kufuneka asebenzise iziphelo zenkqubo yokuwelda ukusombulula ingqibelelo yomqondiso. Designers using this approach can focus on the microstrip length of the shielding copper foil in order to obtain good performance of signal integrity. For systems with dense connectors in the communication structure, the designer can use a PCB as the terminal.

Four, electromagnetic interference

As the speed increases, EMI becomes more and more serious and presents in many aspects (such as electromagnetic interference at interconnects). High-speed devices are particularly sensitive to this and will receive high-speed spurious signals, while low-speed devices will ignore such spurious signals.

There are several ways to eliminate electromagnetic interference in PCB design:

1. Nciphisa iziporo: iluphu nganye ilingana ne-eriyali, kungoko kufuneka sinciphise inani leziporo, indawo yeziporo kunye nempembelelo ye-eriyali. Make sure the signal has only one loop path at any two points, avoid artificial loops and use the power layer whenever possible.

2. Filtering: Filtering can be used to reduce EMI on both the power line and the signal line. There are three methods: decoupling capacitor, EMI filter and magnetic element. EMI filter is shown in Figure 7.

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Umzobo 7: Iindidi zokucoca

3. The shielding. Ngenxa yobude bomcimbi kunye nenqaku elininzi leengxoxo ezikhuselayo, akusekho kwaziswa ngqo.

4. Reduce the speed of high-frequency devices.

5.Yandisa i-dielectric engagungqiyo yebhodi ye-PCB, enokuthintela iindawo ezihamba rhoqo ezinje ngomgca wokuhambisa kufutshane nebhodi ekuphumeni ngaphandle; Increase the thickness of PCB board, minimize the thickness of microstrip line, can prevent electromagnetic line spillover, can also prevent radiation.

At this point, we can conclude that in hf PCB design, we should follow the following principles:

1. Unification and stability of power supply and ground.

2. Carefully considered wiring and proper terminations can eliminate reflections.

3. Carefully considered wiring and proper terminations can reduce capacitive and inductive crosstalk.

4. Ukuncitshiswa kwengxolo kuyadingeka ukufezekisa iimfuno ze-EMC.