A gaskiya ma, buga kewaye hukumar (PCB) are made of electrical linear materials, i.e. their impedance should be constant. Don haka me yasa PCB ke gabatar da rashin daidaituwa cikin sigina? Amsar ita ce shimfidar PCB “ba ta layi-layi” dangane da inda halin yanzu ke gudana.

Ko amplifier yana karɓar halin yanzu daga wata tushe ko wani ya dogara da saurin siginar siginar akan nauyin. Current flows from the power supply, through the bypass capacitor, through the amplifier into the load. The current then travels from the load ground terminal (or shielding of the PCB output connector) back to the ground plane, through the bypass capacitor, and back to the source that originally supplied the current.

The concept of minimum path of current through impedance is incorrect. The amount of current in all different impedance paths is proportional to its conductivity. In a ground plane, there is often more than one low-impedance path through which a large proportion of ground current flows: one path is directly connected to the bypass capacitor; Excayan kuma yana ba da ƙarfin shigarwar shigarwar har sai an kai ƙarfin wucewa. Hoto 1 yana kwatanta waɗannan hanyoyi guda biyu. The backflow current is what’s really causing the problem.

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Lokacin da aka sanya masu wucewa masu wucewa a wurare daban -daban akan PCB, yanayin ƙasa yana gudana ta hanyoyi daban -daban zuwa abubuwan haɓakawa daban -daban, wanda shine ma’anar “rashin daidaituwa na sarari”. If a significant portion of a polar component of the ground current flows through the ground of the input circuit, only that polar component of the signal is disturbed. If the other polarity of the ground current is not disturbed, the input signal voltage changes in a nonlinear manner. Lokacin da aka canza ɓangaren polarity ɗaya amma ɗayan ba haka bane, murdiya yana faruwa kuma yana bayyana azaman hargitsi na biyu na siginar fitarwa. Hoto na 2 yana nuna wannan tasirin murdiya a cikin ƙari.

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Lokacin da ɓangaren polar guda ɗaya kawai na damuwar sine, sakamakon jujjuyawar ba shine raunin sine ba. Daidaita madaidaicin amplifier tare da nauyin 100-and da haɗa haɗin halin yanzu ta hanyar tsayayyar 1-into a cikin wutar lantarki a ƙasa akan siginar siginar guda ɗaya, yana haifar da adadi na 3. Fourier transform shows that the distortion waveform is almost all the second harmonics at -68 DBC. A manyan mitoci, ana iya samar da wannan matakin haɗin gwiwa akan PCB cikin sauƙi, wanda zai iya lalata kyawawan halayen ɓarna na amplifier ba tare da yin amfani da yawancin abubuwan da ba su dace da PCB ba. When the output of a single operational amplifier is distorted due to the ground current path, the ground current flow can be adjusted by rearranging the bypass loop and maintaining distance from the input device, as shown in Figure 4.

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Multiamplifier chip

Matsalar kwakwalwan kwamfuta da yawa (biyu, uku, ko huɗu amplifiers) yana haɗe da rashin iya kiyaye haɗin ƙasa na mai wucewa mai nisa nesa da duk shigarwar. Wannan gaskiya ne musamman ga amplifiers huɗu. Chip-amplifier kwakwalwan kwamfuta suna da tashoshin shigarwa a kowane gefe, don haka babu wani wuri don kewaya hanyoyin da ke rage tashin hankali ga tashar shigarwa.

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Hoto 5 yana nuna hanya mai sauƙi zuwa shimfidar amplifier huɗu. Yawancin na’urori suna haɗa kai tsaye zuwa fil amplifier quad. Ƙarfin wutar lantarki guda ɗaya na iya damun shigar da wutar lantarki na ƙasa da na ƙasa na sauran tashar wutar lantarki, yana haifar da murdiya. Misali, za a iya sanya (+Vs) wucewa capacitor akan tashar 1 na amplifier quad kai tsaye kusa da shigar sa; Za’a iya sanya madaidaicin ƙarfin (-Vs) a ɗayan ɓangaren kunshin. Yanayin ƙasa (+Vs) na iya tayar da tashar 1, yayin da (-vs) na yanzu ba zai iya ba.

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Don gujewa wannan matsalar, bari yanayin ƙasa ya rikitar da shigarwar, amma bari halin yanzu na PCB ya gudana cikin salo na layi -layi. Don cimma wannan, za a iya shirya madaidaicin capacitor akan PCB ta yadda igiyar ƙasa (+Vs) da ( – Vs) ke gudana ta wannan hanya. Idan siginar shigarwa daidai yake da damuwa ta yanayin mai kyau da mara kyau, murdiya ba zai faru ba. Sabili da haka, daidaita madaidaitan abubuwan haɓakawa biyu kusa da juna don su raba maƙasudin ƙasa. Saboda ɓangarorin polar biyu na halin yanzu suna fitowa daga wuri guda (garkuwar haɗin haɗin fitarwa ko ƙasa mai ɗaukar nauyi) kuma duka biyun suna komawa zuwa wuri ɗaya (haɗin ƙasa na gama -gari na kewaya capacitor), tabbatacce/mummunan halin yanzu yana gudana ta hanya ɗaya. Idan juriya na shigar da tashar ta damu da (+Vs) na yanzu, ( – Vs) halin yanzu yana da tasiri iri ɗaya akan sa. Because the resulting disturbance is the same regardless of the polarity, there is no distortion, but a small change in the gain of the channel will occur, as shown in Figure 6.

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Don tabbatar da ƙimar da ke sama, an yi amfani da shimfidu daban-daban na PCB: shimfida mai sauƙi (Hoto 5) da shimfidar ƙasa-ƙasa (Hoto 6). An nuna murdiya da FHP3450 mai ƙaramin aiki mai amfani da huɗu ke amfani da semiconductor na fairchild a cikin tebur 1. An nuna madaidaicin bandwidth na FHP3450 shine 210MHz, gangaren shine 1100V/mu, shigarwar halin yanzu shine 100nA, kuma halin yanzu na aiki a kowace tashar shine 3.6 mA. As can be seen from Table 1, the more distorted the channel, the better the improvement, so that the four channels are nearly equal in performance.

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Without an ideal quad amplifier on a PCB, measuring the effects of a single amplifier channel can be difficult. A bayyane yake, tashar amplifier da aka bayar tana damun ba kawai shigar da kansa ba, har ma da shigar da wasu tashoshi ma. The earth current flows through all the different channel inputs and produces different effects, but is influenced by each output, which is measurable.

Teburin 2 yana nuna jituwa da aka auna akan sauran tashoshin da ba a lalata ba lokacin da tashar guda ɗaya kawai ke tuƙi. Tashar da ba a daidaita ba tana nuna ƙaramin sigina (crosstalk) a madaidaicin mitar, amma kuma tana haifar da murdiya kai tsaye ta yanayin ƙasa ta gabatar idan babu wata alama mai mahimmanci. Siffar karkacewar ƙasa a cikin Hoto na 6 yana nuna cewa halayen jituwa na biyu da jimlar hargitsi (THD) an inganta su sosai saboda kusancin kawar da tasirin ƙasa na yanzu.

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Takaitaccen labarin

Simply put, on a PCB, the backflow current flows through different bypass capacitors (for different power supplies) and the power supply itself, which is proportional to its conductivity. Babban siginar mitar da ke gudana tana komawa zuwa ƙaramin abin ƙera capacitor. Ƙananan mitoci, kamar na siginar sauti, na iya kwarara da farko ta hanyar manyan abubuwan wucewa. Ko da ƙarancin mitar mitar na iya “watsi da” cikakken ikon wucewa da gudana kai tsaye zuwa jagorar wutar. Aikace -aikacen takamaiman zai tantance wace hanya ce mafi mahimmanci. Fortunately, it is easy to protect the entire ground current path by using a common ground point and a ground bypass capacitor on the output side.

Dokar zinare don shimfidar HF PCB shine kiyaye HF kewaye capacitor kusa da fakitin wutar lantarki mai yuwuwa, amma kwatancen Hoto na 5 da Hoto na 6 yana nuna cewa canza wannan dokar don inganta halayen murdiya ba ta da yawa. Ingantattun halaye na murdiya sun zo ne ta hanyar ƙara kusan inci 0.15 na keɓaɓɓen hanyar wucewa ta ƙarfin lantarki, amma wannan yana da ɗan tasiri kan aikin mayar da martani na AC na FHP3450. Tsarin PCB yana da mahimmanci don haɓaka aikin ingantaccen amplifier, kuma batutuwan da aka tattauna anan ba’a iyakance su ga amplifiers hf ba. Ƙananan siginar mitar kamar sauti yana da buƙatun murdiya da yawa. Tasirin ƙasa na yanzu ya yi ƙanƙanta a ƙananan mitoci, amma har yanzu yana iya zama muhimmiyar matsala idan an inganta jigon murdiya da ake buƙata daidai.