Chuong 06 Transistor FET, Mosfet

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Transcript of Chuong 06 Transistor FET, Mosfet

Chng 6:TRANSISTOR TRNG NG FET (FIELD EFFECT TRANSISTOR)ThS. Nguyn B Vng

FET ( Field Effect Transistor) -Transistor hiu ng trng Transistor trng. C 2 loi: - Junction field- effect transistor - vit tt l JFET: Transistor trng iu khin bng tip xc P-N (hay gi l transistor trng mi ni). - Insulated- gate field effect transistor - vit tt l IGFET: Transistor c cc ca cch in. Thng thng lp cch in c dng l lp oxit nn cn gi l metal - oxide - semiconductor transistor (vit tt l MOSFET). Trong loi transistor trng c cc ca cch in c chia lm 2 loi l MOSFET knh sn (DE-MOSFET) v MOSFET knh cm ng (E-MOSFET). Mi loi FET li c phn chia thnh loi knh N v loi knh P.

1. i cng v phn loi

FET

JFET

MOSFET DE-MOSFET E-MOSFET

N

P

N

P

N

P

k hiu

u nhc im ca FET so vi BJT Mt s u im: Dng in qua transistor ch do mt loi ht dn a s to nn. Do vy FET l loi cu kin n cc (unipolar device). FET c tr khng vo rt cao. Ting n trong FET t hn nhiu so vi transistor lng cc. N khng b in p ti dng ID = 0 v do n l ci ngt in tt. C n nh v nhit cao. Tn s lm vic cao. Mt s nhc im: Nhc im chnh ca FET l h s khuch i thp hn nhiu so vi transistor lng cc.

Ging v khc nhau gia FET so vi BJT Ging nhau: S dng lm b khuch i. lm thit b ng ngt bn dn. Thch ng vi nhng mch tr khng. Mt s s khc nhau: BJT phn cc bng dng, cn FET phn cc bng in p. BJT c h s khuch i cao, FET c tr khng vo ln. FET t nhy cm vi nhit , nn thng c s dng trong cc IC tch hp. Trng thi ngt ca FET tt hn so vi BJT

C 2 loi JFET : knh n v knh P. JFET knh n thng thng dng hn. JFET c 3 cc: cc Ngun S (source); cc Ca G (gate); cc Mng D (drain). Cc D v cc S c kt ni vo knh n. cc G c kt ni vo vt liu bn dn pDrain (D) Drain (D)

2. Cu to JFET

Gate (G)

P

N

P

Gate (G)

N

P

N

NSource (S)

PSource (S)

C bn v hot ng ca JFETJFET hot ng ging nh hot ng ca mt kha nc.

Ngun p lc nc-tch ly cc ht e- in cc m ca ngun in p cung cp t D v S. ng nc ra - thiu cc e- hay l trng ti cc dng ca ngun in p cung cp t D v S. iu khin lng ng m nc-in p ti G iu khin rng ca knh n, kim sot dng chy e- trong knh n t S ti D.

s mch JFET

JFET knh N khi cha phn ccDrain (D)

Gate (G)

P

N

P

Source (S)

JFET knh N khi t in p vo D v S, chn G khng kt niID Drain (D)` P P

VDS

Gate (G)

Source (S)

JFET knh N khi phn cc bo haID Drain (D)` P P

VDS

Gate (G)

VGS=0V

Source (S)

JFET knh N phn ccID Drain (D)` P P

VDS

Gate (G)

VGS 1 - i vi transistor JFET knh N th h s khuch i in p khong t 150 ln n 300 ln, cn i vi transistor JFET knh loi P th h s khuch i ch bng mt na l khong t 75 ln n 150 ln.

S mc cc mng chungVDD C1 Uvo RS iG iS C2 URa RS

S mc cc mng chungVDD C1 Uvo RS iG iS C2 URa RS

c im ca s ny c: - Tn hiu vo v tn hiu ra ng pha nhau. - Tr khng vo rt ln Zvo = RGD = - Tr khng ra rt nh - H s khuch i in p < 1 - S cc mng chung c dng rng ri hn, c bn l do n gim c in dung vo ca mch, ng thi c tr khng vo rt ln. S ny thng c dng phi hp tr khng gia cc mch.

S mc cc ca chungS Uvo G D U Ra G

S ny theo nguyn tc khng c s dng do c tr khng vo nh, tr khng ra ln.

Transistor trng loi cc ca cch ly (MOSFET)

Transistor MOSFET y l loi transistor trng c cc ca cch in vi knh dn in bng mt lp cch in mng. Lp cch in thng dng l cht oxit nn ta thng gi tt l transistor trng loi MOS. Tn gi MOS c vit tt t ba t ting Anh l: Metal - Oxide - Semiconductor. Transistor trng MOS c hai loi: transistor MOSFET c knh sn v transistor MOSFET knh cm ng. Trong mi loi MOSFET ny li c hai loi l knh dn loi P v knh loi N.

Cu to ca MOSFET knh sn Transistor trng MOSFET knh sn cn gi l MOSFET-ch ngho (Depletion-Mode MOSFET vit tt l DE-MOSFET). Transistor trng loi MOS c knh sn l loi transistor m khi ch to ngi ta ch to sn knh dn.

Nguyn l hot ng Khi transistor lm vic, thng thng cc ngun S c ni vi v ni t nn US=0. Cc in p t vo cc chn cc ca G v cc mng D l so vi chn cc S. Nguyn tc cung cp ngun in cho cc chn cc sao cho ht dn a s chy t cc ngun S qua knh v cc mng D to nn dng in ID trong mch cc mng. Cn in p t trn cc ca c chiu sao cho MOSFET lm vic ch giu ht dn hoc ch ngho ht dn. Nguyn l lm vic ca hai loi transistor knh P v knh N ging nhau ch c cc tnh ca ngun in cung cp cho cc chn cc l tri du nhau. c tnh truyn t: ID = f(UGS) khi UDS = const

Nguyn l hot ng

c tuyn

a. H c tuyn iu khin ID = f(UGS) khi UDS khng i b. H c tuyn ra ID = f(UDS) khi UGS khng i

Cu to ca MOSFET knh cm ng

Transistor trng loi MOS knh cm ng cn gi l MOSFET ch giu (Enhancement-Mode MOSFET vit tt l E-MOSFET). Khi ch to MOSFET knh cm ng ngi ta khng ch to knh dn. Do cng ngh ch to n gin nn MOSFET knh cm ng c sn xut v s dng nhiu hn.

Nguyn l hot ng E-MOSFET Nguyn l lm vic ca loi knh P v knh N ging ht nhau ch khc nhau v cc tnh ca ngun cung cp t ln cc chn cc. Trc tin, ni cc ngun S vi v ni t, sau cp in p gia cc ca v cc ngun to knh dn.

MOSFET SummaryMOSFET type N-Channel DE-MOSFET N-Channel E-MOSFET P-Channel DE-MOSFET P-Channel E-MOSFET Vgs >0 ON ON OFF OFF Vgs =0 ON OFF ON OFF Vgs RS2 Q1 Q2I D2 = VG R S2

I D2 ID1 = VG R S1 I D1VGS = VG R SI D

0 VG VGS(V)

DE-MOSFET iu hnh kiu tng

Phn cc bng cu chia in th+VDD=+18V R1 110M iG G R2 10M iS S iD RD 1.8k D i DSS=6mA VGS(Off) =-3V ID (mA) 10.67 10 IDQ 7.6 Q

RS 150 0 V GS(Off) -3V -1 1 VG 1.5 V GSQ VGS(V)

Phn cc bng mch hi tip in thiD RG iG G S +V DD RD D iDSS

Mch phn cc E-MOSFET

Phn cc bng hi tip in thiD RG iG G SIDQ 0 V GS(th)

+V DD RD D

VDD RD

ID(mA)

Q

V GSQ VDD

VGS (V)

Phn cc bng cu chia in th+VDD R1 iG G R2 iS S RS IDQ 0 VGS(th) VGSQ VG VGS(V) Q iD RD DVG RD

c tuyn truyn ID(mA) ng phn cc