Dina desain Dewan PCB, ku kanaékan frekuensi anu gancang, bakal aya seueur gangguan anu bénten sareng dewan PCB frékuénsi low. Sumawona, ku ningkatna frékuénsi sareng kontradiksi antara miniaturisasi sareng béaya rendah dewan PCB, gangguan ieu bakal beuki rumit.

Dina panilitian anu saéstuna, urang tiasa nyimpulkeun yén utamina aya opat aspek gangguan, kalebet sora suplai kakuatan, gangguan saluran transmisi, gandeng sareng gangguan éléktromagnétik (EMI). Ngaliwatan nganalisis sababaraha masalah gangguan PCB frékuénsi luhur sareng ngagabungkeun sareng prakték dina padamelan, solusi anu épéktip diteruskeun.

Mimiti, noise power supply

Dina sirkuit frékuénsi luhur, sora suplai kakuatan ngagaduhan pangaruh anu jelas kana sinyal frékuénsi luhur. Therefore, the first requirement of the power supply is low noise. Lantai bersih sami pentingna sareng listrik bersih. Kunaon Karakteristik kakuatan sapertos dina Gambar 1. Jelas, catu daya ngagaduhan impedansi anu tangtu, sareng impedansi didistribusikeun dina sakumna catu daya, janten, sora bakal ditambihan kana catu daya.

Then we should minimize the impedance of the power supply, so it is best to have a dedicated power supply layer and grounding layer. Dina rarancang sirkuit hf, langkung saé pisan mendesain catu daya salaku lapisan tibatan salaku beus dina kaseueuran kasus, supados loop salawasna tiasa nuturkeun jalur impedansi minimal.

Salaku tambahan, papan kakuatan kedah nyayogikeun loop sinyal pikeun sadaya sinyal anu dihasilkeun sareng anu ditampi dina PCB. Ieu ngaminimalkeun loop sinyal sahingga ngirangan noise, anu sering teu dipaliré ku désainer circuit frékuénsi low.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

Gambar 1: Karakteristik kakuatan

Aya sababaraha cara pikeun ngaleungitkeun noise power dina 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. Upami bubuka lapisan catu daya ageung teuing, éta pasti mangaruhan gelung sinyal, sinyalna kapaksa bypass, daérah loop naék, sareng noise naék. At the same time, if several signal lines are clustered near the opening and share the same loop, the common impedance will cause crosstalk. Tempo Gambar 2.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

Gambar 2: Jalur umum gelandang 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. Analog sareng catu daya digital pikeun misahkeun: alat-alat frékuénsi luhur umumna peka pisan kana noise digital, janten kaduana kedah dipisahkeun, dihubungkeun sasarengan dina lawang catu daya, upami sinyal ngalangkungan bagian analog sareng digital tina kecap, tiasa disimpen dina sinyal ngalangkungan gelung pikeun ngirangan daérah gelung. Bentang digital-analog anu digunakeun pikeun sinyal loop ditingalikeun dina Gambar 3.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

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.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

Gambar 4: Tempatkeun kabel listrik di sisi garis sinyal

Two, transmission line

Ngan aya dua kamungkinan saluran transmisi dina PCB:

Masalah panggedena garis pita sareng gelombang mikro nyaéta réfléksi. Réfléksi bakal nyababkeun seueur masalah. Salaku conto, sinyal muatan bakal janten superposisi sinyal aslina sareng sinyal kamandang, anu bakal ningkatkeun kasusah analisis sinyal. Réfléksi nyababkeun leungitna balik (loss loss), anu mangaruhan sinyal sapertos goréng sapertos gangguan aditif:

1. Sinyal anu ngeunteung deui kana sumber sinyal bakal ningkatkeun sora sistem, janten langkung hésé pikeun panarima ngabédakeun noise sareng 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) Nyingkahan impéstansi henteuna jalur transmisi. Titik impedansi henteu teras-terasan nyaéta titik mutasi jalur transmisi, sapertos sudut lempeng, ngalangkungan liang, sareng sajabana, kedah dijauhkeun dugi ka mungkin. Metode: Pikeun nyingkahan juru lempeng tina garis, sajauh mungkin pikeun angkat 45 ° Angle atanapi busur, Angle ageung ogé tiasa; Anggo sakedik ngalangkungan liang, sabab masing-masing ngalangkungan liang mangrupikeun gencatan senjata impedansi, sapertos anu dipidangkeun dina Gbr. 5; Signals from the outer layer avoid passing through the inner layer and vice versa.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

Figure 5: Method for eliminating transmission line interference

(b) Do not use stake lines. Kusabab garis tumpukan naon waé mangrupikeun sumber sora. Upami garis tihang pondok, éta tiasa disambungkeun di tungtung jalur transmisi; Upami garis tihang panjang, éta bakal nyandak jalur transmisi utama salaku sumberna sareng ngahasilkeun réfléksi anu hébat, anu bakal ngahesekeun masalah. Disarankeun henteu nganggo éta.

Katilu, gandengna

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.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

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. Gandeng ieu dikurangan pisan, janten dua kawat tiasa dipintal ngirangan 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 kana jarakna dua loop, ukuran daérah gelung, sareng impedansi tina beban anu kapangaruhan.

5. Kopling kabel listrik: Kabel listrik ac atanapi DC kaganggu ku gangguan éléktromagnétik

Mindahkeun kana alat anu sanés.

There are several ways to eliminate crosstalk in PCB design:

1. Kadua jinis crosstalk ningkat sareng kanaékan impedansi beban, janten garis sinyalna peka kana gangguan anu disababkeun ku crosstalk kedah leres dirobih.

2. Maksimalkeun jarak antara garis sinyal pikeun sacara efektif ngirangan crosstalk kapasitif. Manajemén taneuh, jarak antara kabel (sapertos garis sinyal aktif sareng garis dasar pikeun diasingkeun, khususna dina kaayaan luncat antara garis sinyal sareng ground to interval) sareng ngirangan 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. Pikeun crosstalk anu masuk akal, daérah gelung kedah dileutikan, sareng upami diidinan, gelung kedah dileungitkeun.

5. Avoid signal sharing loops.

6. Nengetan integritas sinyal: désainer kedah nerapkeun tungtung dina prosés las pikeun ngajawab integritas sinyal. Désainer anu nganggo pendekatan ieu tiasa fokus kana panjang microstrip tina foil tambaga taméng supados kéngingkeun performa integritas sinyal anu saé. 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.

Aya sababaraha cara pikeun ngaleungitkeun gangguan éléktromagnétik dina desain PCB:

1. Ngurangan loop: Unggal loop sami sareng anteneu, janten urang kedah ngaleutikan jumlah gelung, luas gelung sareng pangaruh anteneu 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.

Desain PCB frékuénsi luhur lumangsungna solusi gangguan

Gambar 7: Jenis saringan

3. The shielding. Salaku hasil tina panjang masalah ditambah seueur tulisan ngeunaan diskusi diskusi, henteu aya deui perkenalan khusus.

4. Reduce the speed of high-frequency devices.

5. Ningkatkeun konstanta diéléktrik tina papan PCB, anu tiasa nyegah bagian-bagian frékuénsi luhur sapertos jalur transmisi caket papan tina radiasi ka luar; 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. Perhatosan sacara ati-ati kabel sareng penghentian anu leres tiasa ngirangan crosstalk kapasitif sareng induktif.

4. suprési noise diperyogikeun pikeun minuhan sarat EMC.