AMMC-5024 datasheet(8/10 Pages) BOARDCOM

8 / 10 page

Biasing and Operation

AMMC-5024isbiasedwithasinglepositivedrainsupply

(Vdd)anegativegatesupply(Vg1).Forbestoverallperfor-

mancetherecommendedbiasisVdd =7VandIdd=200

mA.Toachievethisdraincurrentlevel,Vg1istypically

between–2.5to–3.5V.Typically,DCcurrentflowforVg1

is–10mA.

TheAMMC-5024hasasecondgatebias(Vg2)thatmaybe

usedforgaincontrol.Whennotbeingutilized,Vg2should

beleftopen-circuited.

Thisfeaturefurtherenhancestheversatilityofapplica-

tions where variable gain over a broad bandwidth is

necessary.

Thissecondgatebias(Vg2)isconnectedtothegatesof

theupperFETsineachcascodestagethroughasmall

de-queingresistor.Theotherendofthegatelineistermi-

natedinanon-chipresistive/diodedividernetwork,which

allowsthesecondgatetoself-bias.Thus,withVg2left

open-circuited,thedraincurrentissetbythe(Vg1)gate

biasvoltageappliedtothelowerFETineachstage.

ThenominalopencircuitvoltageforVg2isapproximately

2volts.Underthisoperatingcondition,maximumgain

andpowerareachievedfromtheTWA.

Byapplyinganexternalvoltagetothesecondgatebias

(Vg2)lessthantheopen-circuitpotential,thedrainvolt-

ageonthelowerFETcanbedecreasedtoapointwhere

thelowerFETentersthelinearoperatingregion.This

reducesthecurrentdrawnbyeachstage.DecreasingVg2

furtherwillreducethedrainvoltageonthelowerFETto-

wardszerowhilepinchingofftheupperFETineachstage.

AtlargernegativevaluesofVg2(between0and-2.5volts)

thegainoftheTWAwilldecreasesignificantly.

Usingthesimplestformofassembly(Figure20),thedevice

iscapableofdeliveringflatgainovera2–50GHzrange

withaminimumofgainslopeandripple.However,this

deviceisdesignedwithDCcoupledRFI/Oports,and

operationmaybeextendedtolowerfrequencies(<2

GHz)throughtheuseofoff-chiplow-frequencyextension

circuitryandproperexternalbiasingcomponents.With

lowfrequencybiasextensionitmaybeusedinavariety

oftime-domainapplications(through40Gb/s).

Figure21showsatypicalassemblyconfiguration.

WhenbypasscapacitorsareconnectedtotheAUXpads,

thelowfrequencylimitisextendeddowntothecorner

frequencydeterminedbythebypasscapacitorandthe

combinationoftheon-chip50ohmloadandsmallde-

queingresistor.Atthisfrequencythesmallsignalgain

willincreaseinmagnitudeandstayatthiselevatedlevel

downtothepointwheretheCauxbypasscapacitoractsas

anopencircuit,effectivelyrollingoffthegaincompletely.

Thelowfrequencylimitcanbeapproximatedfromthe

followingequation:

fCaux =

πCaux(Ro + RDEQ)

where:

Roisthe50Ωgateordrainlineterminationresistor.

RDEQisthesmallseriesde-queingresistorand10Ω.

Cauxisthecapacitanceofthebypasscapacitorcon-

nectedtotheAUXDrainpadinfarads.

WiththeexternalbypasscapacitorsconnectedtotheAUX

gateandAUXdrainpads,gainwillshowaslightincrease

between1.0and1.5GHz.Thisisduetoaseriescombina-

tionofCauxandtheonchipresistancebutisexaggerated

bytheparasiticinductance(Lc)ofthebypasscapacitorand

theinductanceofthebondwire(Ld).Thereforethebond

wirefromtheAuxpadstothebypasscapacitorsshould

bemadeasshortaspossible.

InputandoutputRFportsareDCcoupled;therefore,DC

decouplingcapacitorsarerequiredifthereareDCpaths.

(Donotattempttoapplybiastothesepads.)

RFbondconnectionsshouldbekeptasshortaspossible

toreduceRFleadinductancewhichwilldegradeperfor-

manceabove20GHz.

Anoptionaloutputpowerdetectornetworkisalsopro-

vided.A>0.5µFcapacitorisrequiredfortheDet_Out

padtoexpandpowerdetectionperformancebelow100

MHz.

Groundconnectionsaremadewithplatedthrough-holes

tothebacksideofthedevice;therefore,groundwiresare

notneeded.

AMMC-5024 Datenblatt(PDF) 8 Page - Broadcom Corporation.

AMMC-5024 Datenblatt(HTML) 8 Page - Broadcom Corporation.

Html Pages

1 2 3 4 5 6 7 8 9 10

Datenblatt Download

Link URL