Long Channel Current Equations-6 Increasing Vos causes the channel to acquire a tapered shape.Eventually, as VDs reaches Ves-VTH the channel is pinched off at the drain.Increasing Vos above Ves -VTH has little effect (ideally,no effect)on the channel's shape. ps≥Gs-V, Source Channel Drain UDs =0 Microelectronic Circuits,2004 Oxford University Press When Vos is more than Ves-VTH the channel is pinched off,and the horizontal electric field produces a current. 2西 16
2020/3/7 16 SM 25 EECE 488 ± Set 1: Introduction and Background Long Channel Current Equations - 6 Increasing VDS causes the channel to acquire a tapered shape. Eventually, as VDS reaches VGS ± VTH the channel is pinched off at the drain. Increasing VDS above VGS ± VTH has little effect (ideally, no effect) on the chaQQeO¶V shape. © Microelectronic Circuits, 2004 Oxford University Press When VDS is more than VGS ± VTH the channel is pinched off, and the horizontal electric field produces a current
Long Channel Current Equations -7 If Vos Ves-VTH,the transistor is in saturation (active)region, and the channel is pinched off. Vost Vos2>Vos1 n pinch-off pinch-off: 0 X1 0 V(x1)=VGS-VTH V(x2)=VGS-VTH L VGS-VTH Ipdx=SWCoH [VGs-V(x)-Vmnldv Saturation Region x=0 V=0 Vas3 1 1。=7“C ,(cs-')2 Vas2 Vast Let's,for now,assume that L'=L.The fact that Vos L'is not equal to L is a second-order effect known as channel-length modulation. Since Ip only depends on Ves,MOS transistors in saturation can be used as current sources. 西/日
2020/3/7 17 SM 26 EECE 488 ± Set 1: Introduction and Background Long Channel Current Equations - 7 If VDS > VGS ± VTH, the transistor is in saturation (active) region, and the channel is pinched off. ³ ³ VGS VTH V ox n GS TH L x I Ddx WC V V x V dV 0 ' 0 P [ ( ) ] 2 ( ) 2 ' 1 D n ox VGS VTH L W I P C LeW¶V, for now, assume that L¶=L. The fact that L¶ is not equal to L is a second-order effect known as channel-length modulation. Since ID only depends on VGS, MOS transistors in saturation can be used as current sources
Long Channel Current Equations -8 Current Equation for NMOS: 0 if Vos <VT (Cut-off) C(V)Vnm )(Docp Triod 以c【。o)-r:rara.o-m的 么C.生化s-rgfe>m,a>as-a(am) 西7
2020/3/7 18 SM 27 EECE 488 ± Set 1: Introduction and Background Long Channel Current Equations - 8 Current Equation for NMOS: > @ ° ° ° ° ° ° ° ¯ ° ° ° ° ° ° ° ® ! ! ! ! ( ) ; , ( ) 2 1 ; , ( ) 2 1 ; , 2( ) ( ) 0 ; ( ) 2 2 V V if V V V V V Saturation L W C V V V V if V V V V V Triode L W C V V V if V V V V V Deep Triode L W C if V V Cut off I I n ox GS TH GS TH DS GS TH n ox GS TH DS DS GS TH DS GS TH n ox GS TH DS GS TH DS GS TH GS TH D DS P P P
Long Channel Current Equations -9 。 Current Equation for PMOS: 0;fVsG<ΨHl(Cut-of) 4,C.t(《a-n）nya>ads2 -V)(DeepTrlode) Ip =IsD= a,cng-a)w分周gs>w<-K(Tod j.PC.L.-V.a-WVw)i8Vw-WVw.Vw>Vo-Faul(Somqon) 心2西7 19
2020/3/7 19 SM 28 EECE 488 ± Set 1: Introduction and Background Long Channel Current Equations - 9 Current Equation for PMOS: > @ ° ° ° ° ° ° ° ¯ ° ° ° ° ° ° ° ® ! ! ! ! ( ) ; , ( ) 2 1 ; , ( ) 2 1 ; , 2( ) ( ) 0 ; ( ) 2 2 V V if V V V V V Saturation L W C V V V V if V V V V V Triode L W C V V V if V V V V V Deep Triode L W C if V V Cut off I I p ox SG TH SG TH SD SG TH p ox SG TH SD SD SG TH SD SG TH p ox SG TH SD SG TH SD SG TH SG TH D SD P P P
Regions of Operation-1 Regions of Operation: Cut-off,triode(linear),and saturation (active or pinch-off) ip (mA)A UDS S UGs- Triode Ds≥Gs-V region Saturation region 2.0 gs=V,+2.0 1.5 ≤os=s-V DS %s=V+L.5 1.0 (a) 0.5 s=V,+1.0 %s=V,+0.5 s(V叼 Gs≤V,(cutoff) (b) Microelectronic Circuits,2004 Oxford University Press Once the channel is pinched off,the current through the channel is almost constant.As a result,the I-V curves have a very small slope in the pinch-off (saturation)region,indicating the large channel resistance. 2西/日
2020/3/7 20 SM 29 EECE 488 ± Set 1: Introduction and Background Regions of Operation - 1 Regions of Operation: Cut-off, triode (linear), and saturation (active or pinch-off) © Microelectronic Circuits, 2004 Oxford University Press Once the channel is pinched off, the current through the channel is almost constant. As a result, the I-V curves have a very small slope in the pinch-off (saturation) region, indicating the large channel resistance