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

1. i cng v phn loiFET ( 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.

k hiu

P

N

P

N

P

N

P

N

P

N

P

N

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

2. Cu to JFET 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 p

N

P

P

Drain (D)

Source (S)

Gate (G)

P

N

N

Drain (D)

Source (S)

Gate (G)

P

C bn v hot ng ca JFET

JFET 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 cc

N

P

P

Drain (D)

Source (S)

Gate (G)

JFET knh N khi t in p vo D v S, chn G khng kt ni

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

JFET knh N khi phn cc bo ha

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS=0V

JFET knh N phn cc

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS

JFET knh N ch ngng

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS=-Ve

JFET knh N khi cha phn cc

N

P

P

Drain (D)

Source (S)

Gate (G)

JFET knh N khi t in p vo D v S, chn G khng kt ni

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

JFET knh N khi phn cc bo ha

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS=0V

JFET knh N phn cc

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS

JFET knh N ch ngng

P

P

Drain (D)

Source (S)

Gate (G)

`

VDS

ID

VGS=-Ve

c im hot ng JFETJFET knh N c 3 ch hot ng c bn khi VDS >0:

A.VGS = 0, JFET hot ng bo ha, ID=Max

B.VGS < 0, JFET hot ng tuyn tnh, IDC. VGS =-Vngt, JFET ngng hot ng, ID=0

Nguyn l hot ng ca JFET

c tuyn truyn t

c tuyn ra ca JFET , UGS=const, ID=f(UDS)

0

2

4

6

8

2

4

6

8

10

ID(mA)

UDS(V)

Vng dng in ID khng i

10

UGS=-4V

UGS=-0.5V

UGS=-1V

UGS=-2V

UGS=-0V

Vng thun tr

UDSsat

nh thng

3

Cc cch mc ca JFET trong s mch

S cc ngun chung

S cc ngun chung c im ca s cc ngun chung:

- Tn hiu vo v tn hiu ra ngc pha nhau.- Tr khng vo rt ln Zvo = RGS - Tr khng ra Zra = RD // rd- H s khuch i in p S rd > 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 chung

S mc cc mng chung 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 chung 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 MOSFETy 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.

P

N

P

N

Nguyn l hot ngKhi 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 ib. 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.

P

N

P

N

Nguyn l hot ng E-MOSFETNguyn 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 Summary

MOSFET type Vgs >0 Vgs =0 Vgs

Cch mc MOSFETC 3 cch mc, tng t nh JFET2 cch thng dng nht l cc D chung v cc S chung.

Phn cc JFET v DE-MOSFET iu hnh theo kiu him

Phn cc c nh

0

2

4

6

8

2

4

6

8

10

ID(mA)

VDS(V)

10

VGS=-VGG

VGS=-1V

VGS=-2V

VGS=-0V

Q

VDSQ

ID(mA)

VGS(V)

0

-6

-4

-2

-7

VGS(Off)

Q

VGSQ=-VGG

IDSS

Phn cc t ng

ID(mA)

VGS(V)

0

IDQ

ng phn cc

RS

VGS(Off)

Q

VGSQ

IDSS

Phn cc bng cu chia in th

ID(mA)

VGS(V)

0

VGS(Off)

Q1

VGSQ1

IDSS

DE-MOSFET iu hnh kiu tng

Phn cc bng cu chia in th

Phn cc bng mch hi tip in th

iDSS

+VDD

RD

iD

D

S

G

iG

RG

Mch phn cc E-MOSFET

Phn cc bng hi tip in th

+VDD

RD

iD

D

S

G

iG

RG

ID(mA)

VGS(V)

0

VGSQ

VGS(th)

VDD

Q

IDQ

Phn cc bng cu chia in th

R2

+VDD

RD

iD

D

S

G

iG

RS

iS

R1