I ndearadh PCB bord, le méadú tapa na minicíochta, beidh go leor cur isteach ann atá difriúil ó bhord PCB minicíochta íseal. Thairis sin, agus an mhinicíocht ag méadú agus an contrárthacht idir miniaturization agus costas íseal bord PCB, beidh an cur isteach sin níos casta.

Sa taighde iarbhír, is féidir linn a thabhairt i gcrích go bhfuil ceithre ghné den chur isteach den chuid is mó, lena n-áirítear torann an tsoláthair chumhachta, cur isteach ar an líne tharchuir, cúpláil agus cur isteach leictreamaighnéadach (IEA). Trí anailís a dhéanamh ar fhadhbanna cur isteach éagsúla PCB ardmhinicíochta agus trí chomhcheangal le cleachtas san obair, cuirtear réitigh éifeachtacha ar aghaidh.

Ar dtús, torann an tsoláthair chumhachta

Sa chiorcad ardmhinicíochta, tá tionchar follasach ag torann an tsoláthair chumhachta ar an gcomhartha ardmhinicíochta. Therefore, the first requirement of the power supply is low noise. Tá urlár glan chomh tábhachtach le leictreachas glan. Cén fáth? Taispeántar na tréithe cumhachta i bhFíor 1. Ar ndóigh, tá impedance áirithe ag an soláthar cumhachta, agus déantar an impedance a dháileadh ar an soláthar cumhachta iomlán, dá bhrí sin, cuirfear an torann leis an soláthar cumhachta.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. I ndearadh ciorcad hf, tá sé i bhfad níos fearr an soláthar cumhachta a dhearadh mar chiseal ná mar bhus i bhformhór na gcásanna, ionas gur féidir leis an lúb cosán an impedance íosta a leanúint i gcónaí.

Ina theannta sin, caithfidh an bord cumhachta lúb comhartha a sholáthar do gach comhartha a ghintear agus a fhaightear ar an PCB. Íoslaghdaíonn sé seo an lúb comhartha agus dá bhrí sin laghdaíonn sé torann, rud a mbíonn dearthóirí ciorcad minicíochta íseal ag breathnú air go minic.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

Fíor 1: Saintréithe cumhachta

Tá bealaí éagsúla ann chun deireadh a chur le torann cumhachta i ndearadh PCB:

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. Má tá oscailt an chiseal soláthair cumhachta ró-mhór, tá sé faoi cheangal tionchar a bheith aige ar an lúb comhartha, cuirtear iallach ar an gcomhartha seachbhóthar, méadaíonn an limistéar lúb, agus méadaíonn an torann. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Féach Figiúr 2.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

Fíor 2: Conair choiteann lúb comhartha seachbhóthar

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. Soláthar cumhachta analógach agus digiteach le scaradh: is iondúil go mbíonn feistí ardmhinicíochta an-íogair maidir le torann digiteach, mar sin ba chóir an dá cheann a scaradh, ceangailte le chéile ag bealach isteach an tsoláthair chumhachta, má tá an comhartha trasna na gcodanna analógacha agus digiteacha den focail, is féidir iad a chur sa chomhartha trasna lúb chun an limistéar lúb a laghdú. Taispeántar an réise digiteach-analógach a úsáidtear don lúb comhartha i bhFíor 3.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

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.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

Fíor 4: Cuir an corda cumhachta in aice leis an líne comhartha

Two, transmission line

Níl ach dhá líne tharchuir fhéideartha i PCB:

Is í an fhadhb is mó a bhaineann le líne ribín agus líne micreathonn ná machnamh. Beidh go leor fadhbanna ag baint le machnamh. Mar shampla, beidh an comhartha ualaigh mar superposition an chomhartha bunaidh agus an comhartha macalla, rud a mhéadóidh an deacracht a bhaineann le hanailísiú comhartha. Is cúis le frithchaitheamh caillteanas ar ais (caillteanas ar ais), a théann i bhfeidhm ar an gcomhartha chomh dona le cur isteach torainn breiseáin:

1. Méadóidh an comhartha a léirítear ar ais go foinse na comhartha torann an chórais, rud a fhágfaidh go mbeidh sé níos deacra don ghlacadóir idirdhealú a dhéanamh idir torann agus comhartha;

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) Seachain neamhleanúnachas na línte tarchuir. Is é pointe an impedance neamhleanúnach pointe sóchán na líne tarchuir, mar chúinne díreach, trí pholl, srl., Ba cheart é a sheachaint a mhéid is féidir. Modhanna: Chun coirnéil dhíreacha den líne a sheachaint, chomh fada agus is féidir dul 45 ° Uillinn nó stua, is féidir Uillinn mhór a bheith ann freisin; Bain úsáid as chomh beag agus is féidir trí phoill, toisc gur neamhleanúnachas impedance gach poll trí, mar a thaispeántar 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. Toisc gur foinse torainn aon líne carn. Má tá an líne carn gearr, is féidir í a nascadh ag deireadh na líne tarchuir; Má tá an líne carn fada, glacfaidh sí an phríomhlíne tarchuir mar an foinse agus tabharfaidh sí machnamh iontach, rud a chuirfidh leis an bhfadhb. Moltar gan é a úsáid.

Sa tríú háit, an cúpláil

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.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

Fíor 6: Cúpláil impedance coitianta

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. Laghdaítear an cúpláil seo go mór, mar sin is féidir an dá shreang a thumadh le chéile chun cur isteach a laghdú.

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. Braitheann méid an chrosstalk ionduchtach ar ghaireacht an dá lúb, méid an achair lúb, agus impedance an ualaigh atá buailte.

5. Cúpláil cábla cumhachta: Tá cur isteach leictreamaighnéadach ag cur isteach ar na cáblaí cumhachta ac nó DC

Aistriú chuig gairis eile.

There are several ways to eliminate crosstalk in PCB design:

1. Méadaíonn an dá chineál crosstalk le méadú an impedance ualaigh, mar sin ba cheart na línte comhartha atá íogair do chur isteach de bharr crosstalk a fhoirceannadh i gceart.

2. An fad idir línte comhartha a uasmhéadú chun crosstalk capacitive a laghdú go héifeachtach. Bainistíocht talún, spásáil idir sreangú (cosúil le línte comhartha gníomhacha agus línte talún le haghaidh aonraithe, go háirithe sa staid léim idir an líne comhartha agus an talamh go dtí an t-eatramh) agus ionduchtas luaidhe a laghdú.

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. Maidir le crosstalk ciallmhar, ba cheart an limistéar lúb a íoslaghdú, agus má cheadaítear é, ba cheart an lúb a dhíchur.

5. Avoid signal sharing loops.

6. Tabhair aird ar shláine na comhartha: ba cheart don dearthóir foircinn a chur i bhfeidhm sa phróiseas táthúcháin chun sláine comhartha a réiteach. Is féidir le dearthóirí a úsáideann an cur chuige seo díriú ar fhad micreastruchtúr an scragall copair sciath d’fhonn feidhmíocht mhaith a fháil maidir le sláine comhartha. 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.

Tá bealaí éagsúla ann chun deireadh a chur le trasnaíocht leictreamaighnéadach i ndearadh PCB:

1. Lúbanna a laghdú: Tá gach lúb comhionann le haeróg, mar sin caithfimid líon na lúb, achar na lúb agus éifeacht antenna lúb a íoslaghdú. 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.

Tarlaíonn dearadh cur isteach PCB ardmhinicíochta réitigh chur isteach

Fíor 7: Cineálacha scagtha

3. The shielding. Mar thoradh ar fhad na heisiúna móide go leor alt faoi sciath faoi phlé, ní thugtar isteach a thuilleadh go sonrach.

4. Reduce the speed of high-frequency devices.

5. Tairiseach tréleictreach bhord PCB a mhéadú, rud a d’fhéadfadh cosc ​​a chur ar na codanna ardmhinicíochta amhail an líne tharchuir in aice leis an mbord gathadh amach; 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. Féadann sreangú a mheastar go cúramach agus foirceannadh ceart deireadh a chur le frithchaitheamh.

3. Féadann sreangú a mheastar go cúramach agus foirceannadh ceart crosstalk capacitive agus ionduchtach a laghdú.

4. Teastaíonn cosc ​​torainn chun riachtanais EMC a chomhlíonadh.