Ing desain saka Papan PCB, kanthi paningkatan frekuensi sing cepet, bakal ana akeh gangguan sing beda karo papan PCB frekuensi rendah. Kajaba iku, kanthi nambah frekuensi lan kontradiksi antarane miniaturisasi lan biaya dewan PCB sing murah, gangguan kasebut bakal saya rumit.

Ing panaliten nyata, kita bisa nyimpulake yen utamane ana papat aspek interferensi, kalebu swara sumber listrik, gangguan saluran transmisi, kopling lan gangguan elektromagnetik (EMI). Liwat nganalisa macem-macem masalah gangguan ing PCB frekuensi dhuwur lan nggabungake karo praktik kerja, solusi efektif diwenehake.

Kaping pisanan, gangguan pasokan listrik

Ing sirkuit frekuensi dhuwur, swara pasokan listrik duwe pengaruh sing jelas tumrap sinyal frekuensi dhuwur. Therefore, the first requirement of the power supply is low noise. Lantai sing resik penting banget karo listrik sing resik. Nopo nopo Karakteristik daya ditampilake ing Gambar 1. Temenan, pasokan listrik duwe impedansi tartamtu, lan impedansi disebar liwat kabeh pasokan listrik, mula swara kasebut bakal ditambahake ing pasokan listrik.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Ing desain sirkuit hf, luwih becik ngrancang pasokan listrik minangka lapisan tinimbang bus ing umume kasus, supaya loop kasebut bisa terus ngetutake impedansi minimal.

Kajaba iku, papan listrik kudu nyedhiyakake loop sinyal kanggo kabeh sinyal sing digawe lan ditampa ing PCB. Iki minimalake loop sinyal banjur nyuda swara, sing asring diabaikan dening desainer sirkuit frekuensi rendah.

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Gambar 1: Karakteristik daya

Ana sawetara cara kanggo ngilangi gangguan daya ing desain 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. Yen bukaan lapisan pasokan listrik gedhe banget, mesthine bakal mengaruhi loop sinyal, sinyal bakal dipotong, area gelung mundhak, lan swara tambah akeh. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Deleng Gambar 2.

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Gambar 2: Jalur umum loop sinyal bypass

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. Pasokan listrik analog lan digital kanggo kapisah: piranti frekuensi dhuwur umume sensitif banget marang gangguan digital, mula kalorone kudu dipisahake, disambungake bebarengan ing ngarsane pasokan listrik, yen ana sinyal ing sisih analog lan digital ing tembung, bisa diselehake ing sinyal liwat daur ulang kanggo nyuda area daur ulang. Jangkauan digital-analog sing digunakake kanggo loop sinyal ditampilake ing Gambar 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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Gambar 4: Selehake kabel listrik ing jejere garis sinyal

Two, transmission line

Mung ana rong jalur transmisi ing PCB:

Masalah garis pita lan gelombang mikro paling gedhe yaiku refleksi. Refleksi bakal nyebabake akeh masalah. Contone, sinyal mbukak bakal dadi superposisi sinyal asli lan sinyal kumandhang, sing bakal nambah kangelan analisis sinyal. Refleksi nyebabake kapitunan (loss loss), sing mengaruhi sinyal kaya gangguan gangguan aditif:

1. Sinyal sing dibayangke maneh menyang sumber sinyal bakal nambah swara sistem, saengga luwih angel panrima mbedakake swara saka sinyal;

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) Aja nyegah impedansi garis transmisi. Titik impedansi sing ora terus-terusan yaiku titik mutasi jalur transmisi, kayata pojok lurus, liwat bolongan, lan liya-liyane, kudu dicegah nganti bisa. Cara: Kanggo ngindhari sudhut garis sing lurus, sing paling adoh kanggo mbukak 45 ° Sudut utawa busur, Sudut gedhe uga bisa; Gunakake sawetara liwat bolongan, amarga saben bolongan ora ana impedansi, kayata ing Gambar. 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. Amarga ana garis tumpukan minangka sumber swara. Yen baris tumpukan cekak, bisa disambungake ing pungkasan garis transmisi; Yen baris tumpukan dawa, mula bakal njupuk jalur transmisi utama minangka sumber lan ngasilake refleksi sing gedhe, sing bakal ngrampungake masalah. Disaranake ora nggunakake.

Katelu, kopling

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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Gambar 6: Kopling impedansi umum

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. Kopling iki suda banget, saengga kabel loro kasebut bisa dipintal kanggo nyuda gangguan.

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. Ukuran crosstalk induktif gumantung saka jarak rong loop, ukuran area loop, lan impedansi beban sing kena pengaruh.

5. Kopling kabel listrik: Kabel listrik ac utawa DC diganggu dening gangguan elektromagnetik

Transfer menyang piranti liyane.

There are several ways to eliminate crosstalk in PCB design:

1. Kaloro jinis crosstalk mundhak kanthi nambah impedansi beban, mula garis sinyal sing sensitif marang gangguan sing disebabake crosstalk kudu diakhiri kanthi bener.

2. Ngoptimalake jarak antarane garis sinyal kanthi efektif nyuda crosstalk kapasitif. Manajemen lemah, jarak antarane kabel (kayata garis sinyal aktif lan garis dhasar kanggo diisolasi, utamane ing negara sing mlumpat antarane garis sinyal lan ground to interval) lan nyuda induktansi timah.

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. Kanggo crosstalk sing masuk akal, area loop kudu minimal, lan yen diidini, loop kasebut kudu diilangi.

5. Avoid signal sharing loops.

6. Priksa integritas sinyal: desainer kudu ngetrapake proses las kanggo ngatasi integritas sinyal. Desainer sing nggunakake pendekatan iki bisa fokus ing dawa mikrostrip saka foil tembaga tameng supaya bisa entuk kinerja integritas sinyal sing apik. 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.

Ana sawetara cara kanggo ngilangi gangguan elektromagnetik ing desain PCB:

1. Ngurangi loop: Saben daur ulang padha karo antena, mula kita kudu minimalake jumlah loop, area loop lan efek antena saka loop. 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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Gambar 7: Jinis filter

3. The shielding. Minangka asil saka dawa masalah plus akeh artikel sing nglindhungi diskusi, ora ana perkenalan khusus maneh.

4. Reduce the speed of high-frequency devices.

5. Tambahake konstanta dielektrik ing papan PCB, sing bisa nyegah bagean frekuensi dhuwur kayata garis transmisi ing sacedhake papan sing sumunar metu; 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. Kabel sing dianggep tliti lan mandap sing tepat bisa nyuda crosstalk kapasitif lan induktif.

4. Penekanan swara dibutuhake kanggo memenuhi syarat EMC.