Distributed noise caused by the inherent impedance of the power supply. In high-frequency circuits, power supply noise has a greater impact on high-frequency signals. Therefore, a low-noise power supply is first required. A clean ground is as important as a clean power supply; common-mode field interference. Refers to the noise between the power supply and the ground. It is the interference caused by the common mode voltage caused by the loop formed by the interfered circuit and the common reference surface of a certain power supply. Its value depends on the relative electric field and magnetic field. The strength depends on the strength.

In PCB-soo noqnoqda sare, a more important type of interference is power supply noise. Through systematic analysis of the characteristics and causes of power noise on high-frequency PCB boards, combined with engineering applications, some very effective and simple solutions are proposed.

Falanqaynta qaylada korontada

Sawaxanka korontadu waxa loola jeedaa qaylada ay dhaliso korontada lafteeda ama ay keentay qas. Faragelinta waxaa lagu muujiyey dhinacyada soo socda:

1) Distributed noise caused by the inherent impedance of the power supply itself. In high-frequency circuits, power supply noise has a greater impact on high-frequency signals. Therefore, a low-noise power supply is first required. A clean ground is as important as a clean power source.

Ideally, the power supply has no impedance, so there is no noise. However, the actual power supply has a certain impedance, and the impedance is distributed on the entire power supply. Therefore, noise will also be superimposed on the power supply. Therefore, the impedance of the power supply should be reduced as much as possible, and it is best to have a dedicated power layer and ground layer. In high-frequency circuit design, it is generally better to design the power supply in the form of a layer than in the form of a bus, so that the loop can always follow the path with the least impedance. In addition, the power board must also provide a signal loop for all generated and received signals on the PCB, so that the signal loop can be minimized, thereby reducing noise.

2) Isku xirka khadka korontada. Waxa loola jeedaa ifafaalaha in ka dib markii xadhigga korantada AC ama DC lagu sameeyo faragelinta elektromagnetic, xadhigga korantadu u gudbiyo faragelinta aaladaha kale. Tani waa faragelinta aan tooska ahayn ee sawaxanka korantada ee wareegga-soo noqnoqda sare. Waa in la ogaadaa in sanqadha korontadu aanay ahayn mid iskeed u dhalanaysa, balse ay noqon karto buuqa ka dhashay faragelin dibadeed, ka dibna ku sarraysii sawaxan uu isagu keenay ( shucaac ama haad) si uu u farageliyo wareegyada kale. ama aaladaha.

3) Common mode field interference. Refers to the noise between the power supply and the ground. It is the interference caused by the common mode voltage caused by the loop formed by the interfered circuit and the common reference surface of a certain power supply. Its value depends on the relative electric field and magnetic field. The strength depends on the strength.

Kanaalkan, hoos u dhaca Ic wuxuu keeni doonaa koronto caadi ah oo ku jirta wareegga hadda jira, kaas oo saameyn doona qaybta hesha. Haddii goobta birlabku ay awood badan tahay, qiimaha korantada qaabka caadiga ah ee ka dhalatay wareegga dhulka ee taxanaha ah waa:

Vcm = — (△B/△t) × S (1) ΔB in the formula (1) is the change in magnetic induction intensity, Wb/m2; S is the area, m2.

If it is an electromagnetic field, when its electric field value is known, its induced voltage is:

Vcm = (L×h×F×E/48) (2)

Isla’egta (2) guud ahaan waxay khusaysaa L=150/F ama ka yar, halka F ay tahay inta jeer ee hirarka korantada ee MHz.

If this limit is exceeded, the calculation of the maximum induced voltage can be simplified to:

Vcm = 2×h×E (3) 3) Differential mode field interference. Refers to the interference between the power supply and the input and output power lines. In the actual PCB design, the author found that its proportion in the power supply noise is very small, so it is not necessary to discuss it here.

4) Faragelinta inter-line. Waxa loola jeedaa faragelinta u dhaxaysa xadhkaha korontada. Marka ay jiraan awoodda labada dhinac ee C iyo inductance M1-2 oo u dhexeeya laba wareegyo isku mid ah oo kala duwan, haddii ay jiraan koronto VC iyo hadda IC ee wareegga isha faragelinta, wareegga faragelinta ayaa soo muuqan doona:

a. The voltage coupled through the capacitive impedance is

Vcm = Rv*C1-2*△Vc/△t (4)

In formula (4), Rv is the parallel value of the near-end resistance and the far-end resistance of the interfered circuit.

b. Series resistance through inductive coupling

V = M1-2*△Ic/△t (5)

Haddii uu jiro qaylada qaabka caadiga ah ee isha faragelinta, faragelinta khadka-ilaa-line guud ahaan waxay qaadataa qaab caadi ah iyo qaab kala duwan.

Tallaabooyinka ka hortagga ah ee lagu baabi’inayo faragelinta sawaxanka sawaxanka korantada

In view of the different manifestations and causes of power supply noise interference analyzed above, the conditions under which they occur can be destroyed in a targeted manner, and the interference of power supply noise can be effectively suppressed. The solutions are:

1) Pay attention to the through holes on the board. The through hole requires an opening on the power layer to be etched to leave space for the through hole to pass through. If the opening of the power layer is too large, it will inevitably affect the signal loop, the signal will be forced to bypass, the loop area will increase, and the noise will increase. At the same time, if some signal lines are concentrated near the opening and share this loop, the common impedance will cause crosstalk.

2) Dhig shaandhada qaylada korontada. Waxay si wax ku ool ah u xakameyn kartaa buuqa gudaha sahayda korontada waxayna hagaajin kartaa ka-hortagga faragelinta iyo badbaadada nidaamka. Waana shaandheyn laba-gees ah oo raadiyaha soo noqnoqda, kaas oo aan kaliya sifeyn karin faragelinta buuqa ee laga keenay khadka korontada (si looga hortago faragelinta qalabka kale), sidoo kale sifeyn karta buuqa iskiis u dhashay (si looga fogaado faragelinta qalabka kale). ), oo farageli habka taxanaha ah ee habka caadiga ah. Labaduba waxay leeyihiin saameyn celin.

3) Transformer-ka go’doominta awooda. Kala saar wareegga korantada ama habka caadiga ah ee wareegga dhulka ee fiilada calaamadda, waxay si wax ku ool ah u go’doomin kartaa habka caadiga ah ee hadda jira ee soo noqnoqda sare.

4) Nidaamiyaha tamarta korontada. Dib u soo celinta sahayda tamarta nadiifka ah waxay si weyn u dhimi kartaa heerka buuqa korontada.

5) Xadhkaha goosashada. Xadhkaha wax-soo-saarka iyo soo-saarka tamarta korontada waa in aan la dhigin cidhifka guddiga dielectric, haddii kale way fududahay in la abuuro shucaac oo farageliya wareegyada ama qalabka kale.

6) Separate analog and digital power supplies. High-frequency devices are generally very sensitive to digital noise, so the two should be separated and connected together at the entrance of the power supply. If the signal needs to span both analog and digital parts, a loop can be placed at the signal span to reduce the loop area.

7) Ka fogow in sahay koronto oo kala duwan ay isku-kordhmaan lakabyo kala duwan. Si tartiib ah u rogrogo intii suurtogal ah, haddii kale sanqadha korantada si fudud ayaa loogu lamaaniyaa awoodda dulin.

8) In laga saaro qaybaha xasaasiga ah. Qaybaha qaar, sida loops-locked loops (PLL), waxay aad ugu nugul yihiin sawaxanka korantada. Ka fogee sida ugu macquulsan tamarta korontada.

9) Sufficient ground wires are required for the connecting wires. Each signal needs to have its own dedicated signal loop, and the loop area of ​​the signal and loop is as small as possible, that is to say, the signal and loop must be parallel.

10) Place the power cord. In order to reduce the signal loop, the noise can be reduced by placing the power line on the edge of the signal line.

11) Si looga hortago in sawaxanka korontadu uu faragelin ku sameeyo guddiga wareegga iyo buuqa urursan ee ka dhasha faragelinta dibadda ee korontada, capacitor-ka dhaafa ayaa lagu xiri karaa dhulka jidka faragelinta (marka laga reebo shucaaca), si qaylada waxaa lagu hareer marin karaa dhulka si looga fogaado in la farageliyo qalabka iyo qalabka kale.

gabagabadii

Sawaxanka korontadu waxa uu si toos ah ama si dadban uga soo baxaa korontada waxana uu farageliyaa wareegga. Marka la xakameynayo saameynta ay ku leedahay wareegga, mabda’a guud waa in la raaco. Dhinaca kale, qaylada korontada waa in laga hortago sida ugu macquulsan. Saamaynta wareegga, dhinaca kale, waa in sidoo kale la yareeyo saameynta dibadda ama wareegga korontada, si aysan uga sii darin buuqa korontada.