Haele hantle, boto ea potoloho e hatisitsoeng (PCB) li entsoe ka lisebelisoa tse tsamaeang ka motlakase, ke hore, impedance ea bona e lokela ho lula e le teng. Joale ke hobaneng ha PCB e kenyelletsa nonlinearity ka har’a lets’oao? Karabo ke hore moralo oa PCB ke “sebaka se sa lekanang” mabapi le hore na hona joale ho phalla hokae.

Hore na seholisa se amohela hona joale ho tsoa mohloling o mong kapa ho se seng ho latela polarity ea hanghang ea lets’oao mojaro. 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. Ka sefofaneng sa fatše, hangata ho na le tsela e fetang e le ‘ngoe e tlase ea impedance eo karolo e kholo ea phallo ea lefatše e phallang ka eona: tsela e le’ ngoe e hokahane ka kotloloho le capacitor e fetang; E ‘ngoe e thabisa mohanyetsi oa ho kenya ho fihlela ha capacitor e feta. Setšoantšo sa 1 se bontša litsela tsena tse peli. The backflow current is what’s really causing the problem.

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Ha li-capacitors tse fetang ka nqane li behiloe maemong a fapaneng ho PCB, boemo ba lefatše bo phallela litselaneng tse fapaneng ho ea ho li-capacitor tse fetang, e leng moelelo oa “nonlinearity ea sebaka”. 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. Haeba polarity e ‘ngoe ea hajoale ea lefatše e sa khathatsehe, matla a motlakase a kenang a fetoha ka tsela e sa amaneng le letho. Ha karolo e le ‘ngoe ea polarity e fetoloa empa e’ ngoe e sa fetohe, ho sotha ho ba teng ‘me ho bonahala e le ho sotha ha harmonic ea lets’oao la tlhahiso. Setšoantšo sa 2 se bonts’a phello ena e sothehileng ka mokhoa o feteletsang.

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Ha karolo e le ‘ngoe feela ea pola ea leqhubu la sine e khathatsehile, mofuta o hlahisoang ke leqhubu ha o sa le leqhubu la sine. Ho etsisa seholisa-molumo se phethahetseng ka mojaro oa 100-and le ho kopanya mojaro oa hajoale ka sehanyetsi sa 1-into moeeng oa lefatše ka polarity e le ‘ngoe feela ea lets’oao, ho hlahisa palo ea 3. Fourier transform shows that the distortion waveform is almost all the second harmonics at -68 DBC. Maqhubu a phahameng, boemo bona ba ho hokahana bo hlahisoa habonolo ho PCB, e ka senyang litšobotsi tse ntle tsa ho thibela ho khopama ha seholisa ntle le ho sebelisa boholo ba litlamorao tse ikhethang tsa PCB. 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

Bothata ba li-chip tsa amplifier (tse peli, tse tharo, kapa tse nne tsa amplifiers) li eketsoa ke ho se khone ho boloka khokahano ea lefats’e ea bypass capacitor hole le kenyelletso eohle. Sena ke ‘nete haholo bakeng sa li-amplifi tse nne. Li-chips tsa Quad-amplifier li na le lits’oants’o tsa ho kenya ka lehlakoreng ka leng, ka hona ha ho na sebaka sa lipotoloho tse fetang tse fokotsang tšitiso ho kanale ea ho kenya.

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Setšoantšo sa 5 se bonts’a mokhoa o bonolo oa sebopeho sa li-amplifier tse ‘ne. Lisebelisoa tse ngata li hokela ka kotloloho ho pini ea seholisa sa quad. Matla a phepelo ea motlakase a le mong a ka senya matla a motlakase a kenang le matla a fatše a phepelo e ngoe ea motlakase, a fella ka ho sotha. Mohlala, (+ Vs) bypass capacitor e kanaleng ea 1 ea quad amplifier e ka beoa ka kotloloho haufi le se e se kenyang; (-Vs) bypass capacitor e ka beoa ka lehlakoreng le leng la sephutheloana. Hona joale (+ Vs) mobu oa hona joale o ka senya mocha oa 1, ha motlakase oa (-vs) o sa khone.

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Ho qoba bothata bona, tlohela lefatše hajoale le ferekanye maikutlo, empa tlohella phallo ea hajoale ea PCB e tsamaee hantle. Ho fihlella sena, bypass capacitor e ka hlophisoa ho PCB ka tsela ea hore maqhubu a (+ Vs) le (- Vs) a phalle ka tsela e ts’oanang. Haeba lets’oao la ho kenya le ts’oenngoa ka mokhoa o ts’oanang ke maqhubu a matle le a mabe, ho khopama ho ke ke ha etsahala. Ka hona, hokahanya li-capacitor tse peli tse fetang haufi le tse ling e le hore li arolelane sebaka. Hobane likarolo tse peli tsa polar tsa hajoale tsa lefats’e li tsoa sebakeng se le seng (sehlahisoa se sirelletsang se sirelletsang kapa mojaro oa mojaro) mme ka bobeli li phallela ntlheng e le ‘ngoe (khokahano e tloaelehileng ea lefats’e ea bypass capacitor), boemo bo nepahetseng / bo bobe ba hona joale bo phalla tsela e tšoanang. Haeba khanyetso e kenang ea kanale e ferekanngoa ke (+ Vs) hajoale, (- Vs) hona joale e na le phello e tšoanang ho eona. 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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Ho netefatsa polelo e boletsoeng kaholimo, ho sebelisitsoe meralo e ‘meli e fapaneng ea PCB: sebopeho se bonolo (Setšoantšo sa 5) le sebopeho se sothehileng haholo (Setšoantšo sa 6). Phapang e hlahisitsoeng ke FHP3450 quad-operating amplifier e sebelisang fairchild semiconductor e bonts’oa tafoleng ea 1. Boholo bo tloaelehileng ba FHP3450 ke 210MHz, letsoapo ke 1100V / rona, hona joale leeme la 100nA, ‘me leqhubu la ts’ebetso la kanale ke 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. Ho hlakile hore kanale e fuoeng seholisa e sitisa feela kenyelletso ea eona, empa le kenyelletso ea liteishene tse ling hape. The earth current flows through all the different channel inputs and produces different effects, but is influenced by each output, which is measurable.

Tafole ea 2 e bonts’a li-harmoniki tse lekantsoeng liteisheneng tse ling tse sa sebetsoeng ha ho tsamaisoa mocha o le mong feela. Seteishene se sa sebetsoeng se bonts’a lets’oao le lenyane (crosstalk) ho maqhubu a mantlha, empa hape se hlahisa khopamiso e hlahisitsoeng ka kotloloho ke lefatše hajoale ha ho se na lets’oao la bohlokoa la bohlokoa. Sebopeho sa phokotso e tlase ho Setšoantšo sa 6 se bonts’a hore litšobotsi tsa bobeli tsa harmonic le khokahano ea harmonic (THD) li ntlafalitsoe haholo ka lebaka la pheliso e haufi ea mobu o teng hona joale.

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Kakaretso ea sengoloa sena

Ka mantsoe a bonolo, ho PCB, mokokotlo oa morao-rao o phallela ho li-capacitor tse fapaneng (bakeng sa phepelo e fapaneng ea motlakase) le phepelo ea motlakase ka boeona, e lekanang le ts’ebetso ea eona. Letšoao la maqhubu a phahameng la morao-rao le khutlela ho capacitor e nyane. Maqhubu a maqhubu a tlase, joalo ka a matšoao a molumo, a ka phalla haholoholo ka li-capacitor tse kholoanyane. Le ha maqhubu a tlase a ka “se natse” bokhoni bo felletseng ba ho feta ebe a phalla ka kotlolloho ho lead ea motlakase. Kopo e ikhethileng e tla etsa qeto ea hore na ke tsela efe ea morao-rao e bohlokoa haholo. 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.

Molao oa khauta bakeng sa moralo oa HF PCB ke ho boloka HF bypass capacitor e le haufi le phini ea motlakase ka hohle kamoo ho ka khonehang, empa papiso ea Setšoantšo sa 5 le Setšoantšo sa 6 se bonts’a hore ho fetola molao ona ho ntlafatsa litšobotsi tsa ho khopama ha ho etse phapang e kholo. Litšobotsi tse ntlafalitsoeng tsa ho khopama li bile teng ka lebaka la ho eketsa ka lisenthimithara tse 0.15 tsa maqhubu a maqhubu a phahameng a maqhubu a phahameng, empa sena ha se na tšusumetso e kholo ts’ebetsong ea karabelo ea AC ea FHP3450. Moralo oa PCB o bohlokoa ho ntlafatsa ts’ebetso ea seholisa sa boleng bo holimo, ‘me litaba tse tšohloang mona ha li felle feela ho li-amplifi tsa hf. Matšoao a maqhubu a tlase joalo ka molumo a na le litlhoko tse matla tsa ho sotha. Phello ea hajoale ea mobu e nyane ho maqhubu a tlase, empa e kanna ea ba bothata ba bohlokoa haeba index ea khopamiso e hlokahalang e ntlafatsoa ka nepo.