PCB desain sirkuit sinyal campuran rumit banget. Tata letak lan kabel komponen lan pangolahan sumber daya lan kabel lemah bakal langsung mengaruhi kinerja sirkuit lan kinerja kompatibilitas elektromagnetik. Desain pemisahan saka lemah lan sumber daya ngenalaken ing kertas iki bisa ngoptimalake kinerja sirkuit campuran-sinyal.

Kepiye cara nyuda gangguan antarane sinyal digital lan analog? Rong prinsip dhasar kompatibilitas elektromagnetik (EMC) kudu dimangerteni sadurunge desain: prinsip pisanan yaiku nyilikake area loop saiki; Prinsip kapindho yaiku sistem mung nggunakake siji bidang referensi. On the contrary, if the system has two reference planes, it is possible to form a dipole antenna (note: the radiation of a small dipole antenna is proportional to the length of the line, the amount of current flowing, and the frequency). Yen sinyal ora bali liwat loop paling cilik, antena bunder gedhe bisa kawangun. Avoid both in your design as much as possible.

It has been suggested to separate the digital ground and the analog ground on the mixed-signal circuit board to achieve isolation between the digital ground and the analog ground. Sanajan pendekatan iki bisa ditindakake, ana akeh masalah potensial, utamane ing sistem gedhe lan kompleks. The most critical problem is not to cross the partition gap wiring, once crossed the partition gap wiring, electromagnetic radiation and signal crosstalk will increase dramatically. The most common problem in PCB design is EMI problem caused by signal line crossing the ground or power supply.

As shown in Figure 1, we use the above segmentation method, and the signal line spans the gap between the two ground, what is the return path of the signal current? Suppose the two partitioned lands are connected at some point (usually a single point at one point), in which case the earth current will form a large loop. The high frequency current flowing through the large loop will generate radiation and high ground inductance. If the low level analog current flowing through the large loop is easy to be interfered by external signals. Sing paling awon yaiku nalika bagean kasebut disambungake bebarengan ing sumber daya, puteran saiki sing gedhe banget dibentuk. Kajaba iku, lemah analog lan digital disambungake dening kabel dawa mbentuk antena dipole.

Ngerteni dalan lan mode arus mundur saiki menyang lemah minangka kunci kanggo ngoptimalake desain papan sirkuit sinyal campuran. Many design engineers only consider where the signal current flows, ignoring the specific path of the current. Yen lapisan lemah kudu partitioned lan kudu routed liwat longkangan antarane partisi, sambungan titik siji bisa digawe antarane lemah partitioned kanggo mbentuk jembatan sambungan antarane loro lapisan lemah lan banjur routed liwat jembatan sambungan. In this way, a direct current backflow path can be provided below each signal line, resulting in a small loop area.

Optical isolation devices or transformers can also be used to realize the signal crossing the segmentation gap. Kanggo mantan, iku sinyal optik sing ngluwihi celah segmentasi. Ing kasus trafo, medan magnet sing ngluwihi celah partisi. Sinyal diferensial uga bisa: sinyal mili saka siji baris lan bali saka baris liyane, ing kasus iki digunakake minangka backflow path ora perlu.

To explore the interference of digital signal to analog signal, we must first understand the characteristics of high frequency current. Saiki frekuensi dhuwur tansah milih path karo impedansi paling (induktansi) langsung ngisor sinyal, supaya arus bali bakal mili liwat lapisan sirkuit jejer, preduli saka apa lapisan jejer iku lapisan sumber daya utawa lapisan lemah.

Ing laku, iku umume disenengi kanggo nggunakake partisi PCB seragam menyang bagean analog lan digital. Sinyal analog diarahake ing wilayah analog kabeh lapisan papan, nalika sinyal digital diarahake ing wilayah sirkuit digital. Ing kasus iki, arus bali sinyal digital ora mili menyang lemah sinyal analog.

Interferensi saka sinyal digital kanggo sinyal analog occurs mung nalika sinyal digital routed liwat utawa sinyal analog rute liwat bagean digital saka papan sirkuit. This problem is not due to the lack of segmentation, the real reason is the improper wiring of digital signals.

Desain PCB nggunakake ndadekake, liwat sirkuit digital lan pemisahan sirkuit analog lan wiring sinyal cocok, biasane bisa ngatasi sawetara saka tata letak luwih angel lan masalah wiring, nanging uga ora duwe sawetara alangan potensial disebabake fragmentasi lemah. Ing kasus iki, tata letak lan partisi komponen dadi kritis kanggo nemtokake kualitas desain. If properly laid out, the digital ground current will be limited to the digital part of the board and will not interfere with the analog signal. Such wiring must be carefully checked and checked to ensure 100% compliance with wiring rules. Yen ora, garis sinyal sing ora bener bakal ngrusak papan sirkuit sing apik banget.

When connecting analog and digital ground pins of A/D converters together, most A/D converter manufacturers recommend connecting the AGND and DGND pins to the same low-impedance ground using the shortest leads (Note: Amarga umume chip konverter A/D ora nyambungake lemah analog lan digital bebarengan, lemah analog lan digital kudu disambungake liwat pin eksternal), impedansi eksternal sing disambungake menyang DGND bakal nambah gangguan digital menyang sirkuit analog ing IC liwat parasit. kapasitansi. Dipuntedahaken Rekomendasi iki, loro A / D converter AGND lan pin DGND kudu disambungake menyang lemah analog, nanging pendekatan iki ndadékaké pitakonan kayata apa mburi lemah saka sinyal digital kapasitor decoupling kudu disambungake menyang lemah analog utawa digital.

Yen sistem mung duwe siji konverter A/D, masalah ing ndhuwur bisa gampang ditanggulangi. Minangka ditampilake ing Figure 3, lemah pamisah lan bagean lemah analog lan digital disambungake bebarengan ing A / D rate. When this method is adopted, it is necessary to ensure that the bridge width between the two sites is equal to the IC width, and that no signal line can cross the partition gap.

If the system has many A/D converters, for example, 10 A/D converters how to connect? If analog and digital ground are connected under each A/D converter, A multipoint connection will result, and the isolation between analog and digital ground will be meaningless. Yen ora, sampeyan nglanggar syarat pabrikan.

Cara sing paling apik yaiku miwiti nganggo seragam. As shown in Figure 4, the ground is uniformly divided into analog and digital parts. This layout not only meets the requirements of IC device manufacturers for low impedance connection of analog and digital ground pins, but also avoids EMC problems caused by loop antenna or dipole antenna.

Yen sampeyan duwe mamang babagan pendekatan terpadu saka campuran-sinyal desain PCB, sampeyan bisa nggunakake cara pemisahan lapisan lemah kanggo lay metu lan rute kabeh papan sirkuit. Ing desain, manungsa waé kudu mbayar kanggo nggawe papan sirkuit gampang disambungake bebarengan karo jumper utawa 0 ohm resistor diwenehi jarak kurang saka 1/2 inch loro ing eksperimen mengko. Pay manungsa waé kanggo zoning lan wiring kanggo mesthekake yen ora ana garis sinyal digital ing ndhuwur bagean analog ing kabeh lapisan lan ora ana garis sinyal analog ing ndhuwur bagean digital. Moreover, no signal line should cross the ground gap or divide the gap between the power sources. Kanggo nguji fungsi papan lan kinerja EMC, coba maneh fungsi papan lan kinerja EMC kanthi nyambungake rong lantai bebarengan liwat resistor utawa jumper 0 ohm. Mbandhingake asil tes, ditemokake ing meh kabeh kasus, solusi terpadu luwih unggul saka segi fungsi lan kinerja EMC dibandhingake karo solusi pamisah.

Apa cara pembagian lemah isih bisa digunakake?

Pendekatan iki bisa digunakake ing telung kahanan: sawetara piranti medis mbutuhake arus bocor sing sithik banget ing antarane sirkuit lan sistem sing disambungake menyang pasien; The output of some industrial process control equipment may be connected to noisy and high-power electromechanical equipment; Kasus liyane yaiku nalika LAYOUT PCB tundhuk watesan tartamtu.

Biasane ana sumber daya digital lan analog sing kapisah ing papan PCB sinyal campuran sing bisa lan kudu duwe pasuryan sumber daya pamisah. Nanging, garis sinyal sing cedhak karo lapisan sumber daya ora bisa ngliwati celah ing antarane sumber daya, lan kabeh garis sinyal sing ngliwati celah kasebut kudu ana ing lapisan sirkuit sing cedhak karo area sing gedhe. Ing sawetara kasus, sumber daya analog bisa dirancang karo sambungan PCB tinimbang siji pasuryan supaya daya pasuryan pamisah.

Partition design of mixed signal PCB

Desain PCB sinyal campuran minangka proses sing rumit, proses desain kudu menehi perhatian marang poin ing ngisor iki:

1. Divide the PCB into separate analog and digital parts.

2. Proper component layout.

3. Konverter A / D diselehake ing partisi.

4. Don’t divide the ground. The analog part and the digital part of the circuit board are laid uniformly.

5. Ing kabeh lapisan saka Papan, sinyal digital mung bisa routed ing bagean digital saka Papan.

6. Ing kabeh lapisan saka Papan, sinyal analog mung bisa routed ing bagean analog saka Papan.

7. Analog and digital power separation.

8. Wiring should not span the gap between the split power supply surfaces.

9. Garis sinyal sing kudu span longkangan antarane daya Penyetor pamisah kudu dumunung ing lapisan wiring jejer kanggo wilayah gedhe.

10. Analisa path lan mode aliran saiki bumi.

11. Gunakake aturan wiring bener.