PCB imewe nke mbuaha mgbaàmà sekit bụ nnọọ mgbagwoju anya. Nhazi na wiring nke components na nhazi nke ọkụ ọkụ na waya ala ga-emetụta kpọmkwem arụmọrụ sekit na arụmọrụ ndakọrịta electromagnetic. Nhazi nkebi nke ala na ọkụ ọkụ ewepụtara na akwụkwọ a nwere ike ịkwalite arụmọrụ nke sekit mgbaaka agwakọta.

Kedu ka esi belata nnyonye anya n’etiti akara dijitalụ na analog? A ghaghị ịghọta ụkpụrụ abụọ bụ isi nke ndakọrịta electromagnetic (EMC) tupu imewe: ụkpụrụ nke mbụ bụ ibelata mpaghara nke loop dị ugbu a; Ụkpụrụ nke abụọ bụ na usoro ahụ na-eji naanị otu ụgbọ elu ntụaka. 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). Ọ bụrụ na mgbama ahụ alaghachighị site na akaghị nke kacha nta, enwere ike ịmepụta nnukwu antenna okirikiri. 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. Ọ bụ ezie na ụzọ a ga-ekwe omume, ọ nwere ọtụtụ nsogbu nwere ike ime, karịsịa na nnukwu na usoro mgbagwoju anya. 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. Ihe kachasị njọ bụ na mgbe a na-ejikọta akụkụ ndị ahụ ọnụ na isi iyi ike, a na-emepụta nnukwu oghere dị ugbu a. Na mgbakwunye, ala analọg na dijitalụ ejikọrọ site na ogologo waya na-etolite antenna dipole.

Ịghọta ụzọ na ụdị nke nlọghachi azụ n’ala ugbu a bụ isi ihe iji kwalite nhazi bọọdụ sekit mgbaaka agwakọtara. Many design engineers only consider where the signal current flows, ignoring the specific path of the current. Ọ bụrụ na a ga-ekewapụ ala oyi akwa ma bụrụ nke a ga-emerịrị site na ọdịiche dị n’etiti akụkụ ahụ, enwere ike ịme otu njikọ njikọ n’etiti ala nkewa nkewa iji mepụta njikọ njikọ n’etiti ala abụọ ahụ wee gafere site na njikọ njikọ. 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. Maka nke mbụ, ọ bụ akara ngosi anya nke na-agafe oghere nkewa. N’ihe banyere ihe ntụgharị, ọ bụ oghere ndọta na-agbatị oghere nkebi. Akara ngosi dị iche iche nwekwara ike: akara na-esi n’otu ahịrị na-alọta ma laghachi na nke ọzọ, nke a na-eji ha dị ka ụzọ azụghachi azụ na-enweghị isi.

To explore the interference of digital signal to analog signal, we must first understand the characteristics of high frequency current. Ugboro ugboro ugbu a na-ahọrọ mgbe niile n’okporo ụzọ nwere nkwụsịtụ kacha nta (inductance) ozugbo n’okpuru mgbaàmà ahụ, ya mere, nlọghachi azụ ga-agafe na oyi akwa sekit dị n’akụkụ, n’agbanyeghị ma oyi akwa dị n’akụkụ bụ oyi akwa ike ma ọ bụ ala oyi akwa.

Na omume, a na-ahọrọkarị iji otu PCB nkebi n’ime akụkụ analọgụ na dijitalụ. A na-atụgharị akara ngosi analog na mpaghara analọg nke ọkwa niile nke bọọdụ ahụ, ebe a na-ebugharị akara dijitalụ na mpaghara sekit dijitalụ. N’okwu a, mgbama dijitalụ nke nlọghachi ugbu a anaghị eruba n’ime ala nke mgbaàmà analog.

Ntinye aka sitere na akara dijitalụ gaa na mgbama analọgụ na-apụta naanị mgbe a gafechara akara dijitalụ ma ọ bụ ebugharị akara analọgụ n’akụkụ akụkụ dijitalụ nke bọọdụ sekit. This problem is not due to the lack of segmentation, the real reason is the improper wiring of digital signals.

PCB imewe na-eji n’otu, site na dijitalụ sekit na analọgụ sekit nkebi na kwesịrị ekwesị mgbaàmà wiring, na-emekarị nwere ike dozie ụfọdụ n’ime ndị ọzọ siri ike okirikiri nhọrọ ukwuu na wiring nsogbu, ma ọ dịghị nwekwara ụfọdụ nwere ike nsogbu kpatara ala nkewa. N’okwu a, nhazi na nkewa nke akụkụ na-aghọ ihe dị oké mkpa n’ịchọpụta àgwà nke nhazi ahụ. 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. Ma ọ bụghị ya, akara mgbaàmà na-ezighị ezi ga-ebibi kpamkpam osisi sekit dị ezigbo mma.

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: N’ihi na ọtụtụ ihe ntụgharị A / D anaghị ejikọta ala analog na dijitalụ ọnụ n’ime, analog na ala dijitalụ ga-ejikọta ya site na ntụtụ mpụga), mgbochi ọ bụla nke mpụga ejikọrọ na DGND ga-ejikọta ụda dijitalụ ọzọ na sekit analog n’ime IC site na parasitic. ikike. N’ịgbaso ndụmọdụ a, ma ihe ntụgharị A/D AGND na DGND kwesịrị ijikọ na ala analọg, mana usoro a na-ewelite ajụjụ dịka ma njedebe ala nke akara ngosi dijitalụ decoupling capacitor kwesịrị jikọọ na ala analog ma ọ bụ dijitalụ.

Ọ bụrụ na sistemụ nwere naanị otu onye ntụgharị A/D, enwere ike idozi nsogbu a dị n’elu ngwa ngwa. Dịka e gosiri na eserese 3, a na-ekewa ala na mpaghara ala analog na dijitalụ jikọtara ọnụ n’okpuru ihe ntụgharị A/D. 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. Ọ bụrụ na ịmeghị, ị ga-emebi ihe ndị nrụpụta chọrọ.

Ụzọ kachasị mma bụ ịmalite na uwe. 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.

Ọ bụrụ na ị nwere obi abụọ banyere ịdị n’otu obibia nke mbuaha-signal PCB imewe, ị nwere ike iji usoro nke ala oyi akwa nkebi ka tọgbọrọ na ụzọ dum sekit osisi. N’ime imewe ahụ, a ga-akwụ ụgwọ nlebara anya iji mee ka bọọdụ sekit dị mfe ijikọ ọnụ na jumpers ma ọ bụ 0 ohm resistors na-erughị 1/2 inch iche na nnwale ikpeazụ. Lezienụ anya na zoning na wiring iji hụ na ọ nweghị ahịrị mgbaama dijitalụ dị n’elu ngalaba analọgụ na ọkwa niile yana na ọ nweghị ahịrị mgbama analog dị n’elu ngalaba dijitalụ. Moreover, no signal line should cross the ground gap or divide the gap between the power sources. Iji nwalee ọrụ bọọdụ na arụmọrụ EMC, rụgharịa ọrụ osisi na arụmọrụ EMC site na ijikọ ala abụọ ọnụ site na 0 ohm resistor ma ọ bụ jumper. N’ịtụle nsonaazụ ule ahụ, achọpụtara na ihe fọrọ nke nta ka ọ bụrụ ihe niile, ngwọta dị n’otu dị elu karịa ọrụ na arụmọrụ EMC ma e jiri ya tụnyere ngwọta nkewa.

Usoro nke nkesa ala ka na-arụ ọrụ?

Enwere ike iji usoro a mee ihe n’ọnọdụ atọ: ụfọdụ ngwaọrụ ahụike chọrọ obere ntapu ugbu a n’etiti sekit na sistemu ejikọrọ na onye ọrịa; The output of some industrial process control equipment may be connected to noisy and high-power electromechanical equipment; Ikpe ọzọ bụ mgbe LAYOUT nke PCB nọ n’okpuru mmachi akọwapụtara.

A na-enwekarị ọkụ dijitalụ na analọg dị iche iche na bọọdụ PCB mgbama agwakọta nke nwere ike ma kwesị inwe ihu ọkọnọ ike gbawara agbawa. Otú ọ dị, akara mgbaàmà ndị dị n’akụkụ oyi akwa ọkụ enweghị ike ịgafe ọdịiche dị n’etiti ihe ndị na-enye ọkụ, na akara ngosi niile na-agafe oghere ahụ ga-adịrịrị na oyi akwa sekit dị n’akụkụ nnukwu ebe. N’ọnọdụ ụfọdụ, enwere ike iji njikọ PCB mepụta ọkụ analọgụ karịa otu ihu iji zere ikewa ihu ike.

Partition design of mixed signal PCB

Ngwakọta-ngwakọ PCB imewe bụ usoro dị mgbagwoju anya, usoro nhazi kwesịrị ịṅa ntị na isi ihe ndị a:

1. Kewaa PCB n’ime akụkụ analog na dijitalụ dị iche iche.

2. Nhazi akụrụngwa kwesịrị ekwesị.

3. A na-etinye ihe ntụgharị A / D n’ofe nkebi.

4. Ekewala ala. The analog part and the digital part of the circuit board are laid uniformly.

5. N’ígwé niile nke osisi ahụ, akara ngosi dijitalụ nwere ike ịmegharị naanị na akụkụ dijitalụ nke osisi ahụ.

6. N’ígwé niile nke osisi ahụ, akara ngosi analog nwere ike ịmegharị naanị na akụkụ analog nke osisi ahụ.

7. Analog and digital power separation.

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

9. Ahịrị mgbaàmà nke ga-agbatị ọdịiche dị n’etiti ihe ndị na-enye ike kewara kwesịrị ịdị na wiring oyi akwa n’akụkụ nnukwu ebe.

10. Nyochaa n’ezie ụzọ na mode nke ụwa ugbu a eruba.

11. Jiri iwu waya ziri ezi.