Hauv kev tsim ntawm PCB pawg thawj coj saib, nrog rau kev nce nrawm dua, yuav muaj kev cuam tshuam ntau uas txawv ntawm qhov tsawg-tsawg PCB board. Ntxiv mus, nrog kev nce ntau zaus thiab qhov tsis sib xws ntawm kev ua haujlwm me me thiab tus nqi qis ntawm PCB pawg thawj coj, cov cuam tshuam no yuav dhau los ua qhov nyuaj dua.

Hauv qhov kev tshawb fawb tiag tiag, peb tuaj yeem xaus tias muaj plaub feem ntawm kev cuam tshuam, suav nrog lub zog hluav taws xob suab nrov, kev cuam tshuam kab kev cuam tshuam, kev sib txuas thiab kev cuam tshuam hluav taws xob (EMI). Los ntawm kev txheeb xyuas ntau yam teeb meem cuam tshuam ntawm PCB ntau zaus thiab ua ke nrog kev xyaum ua haujlwm, cov kev daws teeb meem tau muab tso rau pem hauv ntej.

Ua ntej, lub hwj chim muab suab nrov

Hauv kev siv hluav taws xob ntau zaus, lub suab nrov ntawm lub zog xa khoom muaj qhov cuam tshuam pom tseeb ntawm lub teeb liab zaus. Therefore, the first requirement of the power supply is low noise. Cov plag tsev huv yog qhov tseem ceeb ib yam li hluav taws xob huv. Vim li cas? Cov yam ntxwv fais fab tau qhia hauv daim duab 1. Pom tseeb, lub zog siv hluav taws xob muaj qee qhov cuam tshuam, thiab qhov cuam tshuam tau muab faib rau tag nrho cov khoom siv hluav taws xob, yog li ntawd, lub suab nrov yuav ntxiv rau lub hwj chim.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Hauv kev tsim hluav taws xob hf, nws zoo dua los tsim cov khoom siv hluav taws xob ua ib txheej ntau dua li lub tsheb npav feem ntau, yog li ntawd lub voj tuaj yeem ua raws txoj hauv kev ntawm qhov cuam tshuam tsawg.

Ib qho ntxiv, pawg thawj coj saib xyuas hluav taws xob yuav tsum muab lub teeb liab rau txhua qhov tsim tawm thiab tau txais cov cim ntawm PCB. Qhov no txo ​​qis lub teeb liab lub voj thiab yog li txo cov suab nrov, uas feem ntau raug saib xyuas los ntawm cov neeg tsim hluav taws xob tsawg zaus.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Daim duab 1: Cov yam ntxwv muaj zog

Muaj ntau txoj hauv kev los tshem tawm lub suab nrov hauv PCB tsim:

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. Yog tias qhib cov txheej txheem hluav taws xob loj dhau, nws tau cuam tshuam rau lub teeb liab lub voj, lub teeb liab raug yuam kom hla, thaj tsam hauv lub voj nce, thiab lub suab nrov nce. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Saib Daim Duab 2.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Daim duab 2: Txoj hauv kev hla dhau lub teeb liab lub voj

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. Kev sib piv thiab cov khoom siv hluav taws xob los sib cais: cov khoom siv ntau zaus feem ntau nkag siab zoo rau cov suab nrov digital, yog li ob qho yuav tsum tau sib cais, txuas ua ke ntawm qhov nkag ntawm lub zog xa khoom, yog tias lub teeb liab hla qhov sib piv thiab digital ntawm cov lus, tuaj yeem muab tso rau hauv lub teeb liab hla lub voj kom txo qis lub voj. Qhov sib piv digital-analog siv rau lub voj teeb liab tau qhia hauv daim duab 3.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

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.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Daim duab 4: Tso lub hwj huam qaum ib sab ntawm kab teeb liab

Two, transmission line

Tsuas muaj ob txoj hauv kev sib kis tau hauv PCB:

Qhov teeb meem loj tshaj plaws ntawm kab kab thiab kab microwave yog kev xav. Kev xav yuav ua rau muaj teeb meem ntau yam. Piv txwv li, lub teeb liab thauj khoom yuav yog kev tshaj tawm ntawm thawj lub teeb liab thiab lub suab ncho, uas yuav ua rau muaj teeb meem nyuaj ntawm kev ntsuas lub teeb liab. Kev xav ua rau poob rov qab (rov poob), uas cuam tshuam rau lub teeb liab tsis zoo li kev cuam tshuam suab nrov ntxiv:

1. Lub teeb pom kev rov qab mus rau qhov chaw teeb liab yuav ua rau lub suab nrov ntawm lub kaw lus, ua rau nws nyuaj rau tus neeg txais lub suab kom paub qhov txawv lub suab nrov ntawm lub teeb liab;

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) Tsis txhob cuam tshuam kev cuam tshuam tsis tu ncua ntawm cov kab sib kis. Lub ntsiab lus ntawm kev cuam tshuam tsis tu ncua yog lub ntsiab lus ntawm kev hloov pauv kab, xws li lub ces kaum ncaj, hla lub qhov, thiab lwm yam, yuav tsum zam kom deb li deb tau. Txoj hauv kev: Txhawm rau zam cov ces kaum ncaj ntawm kab, kom deb li deb tau mus rau 45 ° Lub kaum ntse ntse lossis lub kaum ntse ntse, Lub Loj Loj kuj tseem tuaj yeem yog; Siv tsawg ob qhov los ntawm qhov ua tau, vim tias txhua qhov dhau los yog qhov cuam tshuam tsis sib xws, raws li qhia hauv Duab. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Vim tias ib pawg kab twg yog lub suab nrov. Yog tias pawg kab luv, nws tuaj yeem txuas nrog qhov kawg ntawm txoj kab sib kis; Yog tias pawg kab ntev, nws yuav siv txoj kab sib kis tseem ceeb ua lub hauv paus thiab tsim kev xav zoo, uas yuav ua rau muaj teeb meem nyuaj. Nws raug nquahu kom tsis txhob siv nws.

Thib peb, kev sib txuas

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.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Daim duab 6: Kev sib txuas tsis sib xws

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. Qhov kev sib txuas no tau txo qis heev, yog li ob lub xov hlau tuaj yeem sib tw ua ke kom txo qis kev cuam tshuam.

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. Qhov loj me ntawm cov khoom siv sib dhos nyob ntawm qhov sib thooj ntawm ob lub voj, qhov loj ntawm thaj tsam ntawm lub voj, thiab qhov cuam tshuam ntawm lub nra cuam tshuam.

5. Lub zog txuas hluav taws xob txuas: Cov hluav taws xob ac lossis DC raug cuam tshuam los ntawm kev cuam tshuam hluav taws xob

Hloov mus rau lwm yam khoom siv.

There are several ways to eliminate crosstalk in PCB design:

1. Ob hom crosstalk nce nrog qhov nce ntawm qhov load impedance, yog li cov teeb liab kab nkag mus cuam tshuam los ntawm crosstalk yuav tsum raug txiav kom raug.

2. Ua kom nrug deb ntawm kab teeb liab kom muaj txiaj ntsig zoo txo ​​cov peev txheej sib tw. Kev tswj hauv av, sib nrug nruab nrab ntawm cov xov hlau (xws li cov kab teeb liab nquag siv thiab cov kab hauv av rau kev sib cais, tshwj xeeb tshaj yog nyob hauv lub xeev dhia ntawm kab teeb liab thiab hauv av mus rau ntu) thiab txo cov hlau lead inductance.

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. Rau kev nkag siab zoo crosstalk, thaj tsam ntawm lub voj yuav tsum tau txo qis, thiab yog tias tso cai, lub voj yuav tsum raug tshem tawm.

5. Avoid signal sharing loops.

6. Ua tib zoo saib xyuas lub teeb liab ncaj ncees: tus tsim qauv yuav tsum ua tiav qhov txheej txheem vuam txhawm rau daws teeb meem kev ncaj ncees. Cov neeg tsim qauv siv txoj hauv kev no tuaj yeem tsom mus rau microstrip ntev ntawm cov ntaub thaiv npog tooj liab txhawm rau kom tau txais txiaj ntsig zoo ntawm kev teeb tsa kev ncaj ncees. 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.

Muaj ntau txoj hauv kev los tshem tawm kev cuam tshuam hluav taws xob hauv PCB tsim:

1. Txo cov loops: Txhua lub voj sib npaug rau lub kav hlau txais xov, yog li peb yuav tsum txo tus naj npawb ntawm cov loops, thaj tsam ntawm cov loops thiab cov kav hlau txais xov cuam tshuam ntawm loops. 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.

Kev tsim PCB ntau zaus tshwm sim cuam tshuam kev daws teeb meem

Daim duab 7: Lim hom

3. The shielding. Raws li qhov ntev ntawm qhov teeb meem ntxiv rau ntau qhov kev sib tham tiv thaiv kab lus, tsis qhia tshwj xeeb ntxiv lawm.

4. Reduce the speed of high-frequency devices.

5. Ua kom lub dielectric tsis tu ncua ntawm PCB pawg thawj coj saib, uas tuaj yeem tiv thaiv qhov feem ntau zaus xws li cov kab sib kis nyob ze ntawm lub rooj tsavxwm los ntawm kev tawm sab nraud; 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. Ua tib zoo xav txog cov thaiv thiab kev txiav tawm kom raug tuaj yeem tshem tawm qhov xav tau.

3. Ua tib zoo xav txog cov thaiv thiab kev txiav tawm kom raug tuaj yeem txo qhov muaj peev xwm thiab khaus khaus khaus.

4. Lub suab nrov yuav tsum ua kom tau raws li EMC cov cai.