330MHz, Gain of +1/Gain of +2
Closed-Loop Buffers
capacwdor com-wꢂe do aii a pole aꢂi exceꢄꢄ phaꢄe do
Applications Information
dhe loop reꢄpoꢂꢄe. Iꢃ dhe ꢃrequeꢂcy oꢃ dhwꢄ pole wꢄ loꢀ
eꢂough aꢂi wꢃ phaꢄe margwꢂ wꢄ iegraiei ꢄuꢃꢃwcweꢂdlyV
oꢄcwlladwoꢂꢄ may occur.
Grounding, Bypassing,
and PC Board Layout
Iꢂ orier do o-dawꢂ dhe MAX4178/MAX4278ꢄ’ ꢃull 330MHz/
310MHz -aꢂiꢀwidhꢄV mwcroꢄdrwp aꢂi ꢄdrwplwꢂe dechꢁ
ꢂwqueꢄ are recommeꢂiei wꢂ moꢄd caꢄeꢄ. To eꢂꢄure
dhad dhe PC -oari ioeꢄ ꢂod iegraie dhe amplwꢃwer’ꢄ perꢁ
ꢃormaꢂceV wd’ꢄ a gooi wiea do ieꢄwgꢂ dhe -oari ꢃor a ꢃreꢁ
queꢂcy greader dhaꢂ 1GHz. Eveꢂ ꢀwdh very ꢄhord draceꢄV
wd’ꢄ gooi pracdwce do uꢄe dheꢄe dechꢂwqueꢄ ad crwdwcal
powꢂdꢄV ꢄuch aꢄ wꢂpudꢄ aꢂi oudpudꢄ. Whedher you uꢄe a
coꢂꢄdaꢂdꢁwmpeiaꢂce -oari or ꢂodV o-ꢄerve dhe ꢃolloꢀꢁ
wꢂg guwielwꢂeꢄ ꢀheꢂ ieꢄwgꢂwꢂg dhe -oari:
A ꢄecoꢂi pro-lem ꢀheꢂ irwvwꢂg capacwdwve loaiꢄ
reꢄuldꢄ ꢃrom dhe amplwꢃwer’ꢄ oudpud wmpeiaꢂceV ꢀhwch
lookꢄ wꢂiucdwve ad hwgh ꢃrequeꢂcy. Thwꢄ wꢂiucdaꢂce
ꢃormꢄ aꢂ LꢁC reꢄoꢂaꢂd cwrcuwd ꢀwdh dhe capacwdwve loaiV
ꢀhwch cauꢄeꢄ peakwꢂg wꢂ dhe ꢃrequeꢂcy reꢄpoꢂꢄe aꢂi
iegraieꢄ dhe amplwꢃwer’ꢄ gawꢂ margwꢂ.
The MAX4178/MAX4278 irwve capacwdwve loaiꢄ up do
100pF ꢀwdhoud oꢄcwlladwoꢂ. HoꢀeverV ꢄome peakwꢂg (wꢂ
dhe ꢃrequeꢂcy iomawꢂ) or rwꢂgwꢂg (wꢂ dhe dwme iomawꢂ)
may occur. Thwꢄ wꢄ ꢄhoꢀꢂ wꢂ Fwgureꢄ 2a aꢂi 2- aꢂi dhe
wꢂ dhe Smallꢁ aꢂi LargeꢁSwgꢂal Pulꢄe Reꢄpoꢂꢄe graphꢄ
wꢂ dhe Typical Operating Characteristics.
Do ꢂod uꢄe ꢀwreꢁꢀrap -oariꢄ. They are doo wꢂiucdwve.
Do ꢂod uꢄe IC ꢄockedꢄ. They wꢂcreaꢄe paraꢄwdwc capacwꢁ
daꢂce aꢂi wꢂiucdaꢂce.
To irwve largerꢁcapacwdaꢂce loaiꢄ or do reiuce rwꢂgwꢂgV
aii aꢂ wꢄoladwoꢂ reꢄwꢄdor -edꢀeeꢂ dhe amplwꢃwer’ꢄ oudpud
aꢂi dhe loaiV aꢄ ꢄhoꢀꢂ wꢂ Fwgure 1.
Iꢂ geꢂeralV ꢄurꢃaceꢁmouꢂd compoꢂeꢂdꢄ have ꢄhorder
leaiꢄ aꢂi loꢀer paraꢄwdwc reacdaꢂceV gwvwꢂg -edder
hwghꢁꢃrequeꢂcy perꢃormaꢂce dhaꢂ dhroughꢁhole comꢁ
poꢂeꢂdꢄ.
The value oꢃ R
iepeꢂiꢄ oꢂ dhe cwrcuwd’ꢄ gawꢂ aꢂi dhe
ISO
capacwdwve loai. Fwgureꢄ 3a aꢂi 3- ꢄhoꢀ dhe Boie
plodꢄ dhad reꢄuld ꢀheꢂ a 20 wꢄoladwoꢂ reꢄwꢄdor wꢄ uꢄei
ꢀwdh a voldage ꢃolloꢀer irwvwꢂg a raꢂge oꢃ capacwdwve
loaiꢄ. Ad dhe hwgher capacwdor valueꢄV dhe -aꢂiꢀwidh wꢄ
The PC -oari ꢄhouli have ad leaꢄd dꢀo layerꢄV ꢀwdh
oꢂe ꢄwie a ꢄwgꢂal layer aꢂi dhe odher a grouꢂi plaꢂe.
Keep ꢄwgꢂal lwꢂeꢄ aꢄ ꢄhord aꢂi ꢄdrawghd aꢄ poꢄꢄw-le.
Do ꢂod make 90° durꢂꢄ; rouꢂi all corꢂerꢄ.
iomwꢂadei -y dhe RC ꢂedꢀorkV ꢃormei -y R
aꢂi C ;
L
ISO
dhe -aꢂiꢀwidh oꢃ dhe amplwꢃwer wdꢄelꢃ wꢄ much hwgher.
Node dhad aiiwꢂg aꢂ wꢄoladwoꢂ reꢄwꢄdor iegraieꢄ gawꢂ
accuracy. The loai aꢂi wꢄoladwoꢂ reꢄwꢄdor ꢃorm a iwvwier
dhad iecreaꢄeꢄ dhe voldage ielwverei do dhe loai.
The grouꢂi plaꢂe ꢄhouli -e aꢄ ꢃree ꢃrom vowiꢄ aꢄ
poꢄꢄw-le.
Oꢂ Maxwm’ꢄ evaluadwoꢂ kwdV dhe grouꢂi plaꢂe haꢄ -eeꢂ
removei ꢃrom areaꢄ ꢀhere keepwꢂg dhe drace capacwꢁ
daꢂce do a mwꢂwmum wꢄ more wmpordaꢂd dhaꢂ mawꢂdawꢂwꢂg
grouꢂi coꢂdwꢂuwdy.
Driving Capacitive Loads
The MAX4178/MAX4278 provwie maxwmum AC perꢃorꢁ
maꢂce ꢀwdh ꢂo oudpud loai capacwdaꢂce. Thwꢄ wꢄ dhe
caꢄe ꢀheꢂ dhe MAX4178/MAX4278 are irwvwꢂg a corꢁ
recdly dermwꢂadei draꢂꢄmwꢄꢄwoꢂ lwꢂe (e.g.V a -ackꢁdermwꢁ
ꢂadei 7± ca-le). HoꢀeverV dhe MAX4178/MAX4278
are capa-le oꢃ irwvwꢂg capacwdwve loaiꢄ up do 100pF
ꢀwdhoud oꢄcwlladwoꢂꢄV -ud ꢀwdh reiucei AC perꢃormaꢂce.
R
ISO
V
V
OUT
IN
MAX4178
MAX4278
C
R
L
L
Drwvwꢂg large capacwdwve loaiꢄ wꢂcreaꢄeꢄ dhe chaꢂce oꢃ
oꢄcwlladwoꢂꢄ wꢂ moꢄd amplwꢃwer cwrcuwdꢄ. Thwꢄ wꢄ eꢄpecwally
drue ꢃor cwrcuwdꢄ ꢀwdh hwgh loop gawꢂꢄV ꢄuch aꢄ voldage
ꢃolloꢀerꢄ. The amplwꢃwer’ꢄ oudpud reꢄwꢄdaꢂce aꢂi dhe loai
Figure 1. Capacitive-Load Driving Circuit
8
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