INF3410 — Fall 2016
Transcript of INF3410 — Fall 2016
INF3410 — Fall 2016
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs)
Content
CMOS FET Large Signal Models (book 5.1-5.2)
MOSFET circuits at DC (book 5.3)
Further Model Refinements (book 5.4, will be discussedlater)
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 2
Content
CMOS FET Large Signal Models (book 5.1-5.2)
MOSFET circuits at DC (book 5.3)
Further Model Refinements (book 5.4, will be discussedlater)
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 3
Device Concept
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 4
Device Cross Section
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 5
Short Sidetrack: PN-junction
(from book: Carusone, Johns, Martin)
Cj =Cj0
r
1 + VRΦ0
(1.17)
Cj0 =
√
√
√qKSϵ0
2Φ0
NAND
NA +ND(1.18)
Φ0 = UT ln
�
NAND
n2i
�
(1.6)
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 6
nFET/NMOS and pFET/PMOS cross section
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 7
Above Threshold Regions of Operation NFET
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 8
Above Threshold Regions of Operation PFET
’Above Threshold’ is also called ’Strong Inversion’
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 9
nMOSFET Device Symbols
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 10
pMOSFET Device Symbols
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 11
The EKV model
iD = iF − iR
iF(R) = IS ln�
1 + evG−Vtn−nvS(D)
nVT
�2
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 12
Regions of operation dependent on vGS:strong- vs weak inversion
weak inversion = subthreshold vs. strong inversion =above thresholdThese are dependent on vGS ≥ Vtn for strong inversionand VGS < Vtn for weak inversion. The transitionbetween the two is refered to as moderate inversion.
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 13
Regions of operation dependent on vDS:triode- vs active region
INDEPENDENT of weak- and strong inversion thetransistor can operate in either:Triode region = ’linear’ region vs. saturation = activeregionThese are dependent on vDS ≥ Vsat for active region andvDS < Vsat for triode region, where the definition of Vsatis different dependent on if the transistor is in weak(Vsat ≈ 4VT)or strong inversion (Vsat = VOV).
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 14
Regions of operation summary
So there are 4 differnt combinations possible:weak inversion, triode region OR weak inversion, activeregion OR strong inversion, triode region OR stronginversion, active region!
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 15
strong inversion, active region
iD =1
2nkn (vOV − nvS)2 (1 + λvDS)
Different name in the EKV model: β := kn and 1 ≤ n ≤ 2and often n ≈ 1 and is neglected
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 16
weak inversion, active region
iD = ISevG−Vtn−nvS
nVT (1 + λvDS) (16.13)
Where IS = 2nknV2T
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 17
strong inversion, triode region
EKV:iD = knvDS
�
vOV −n
2(vD + vS)
�
Sedra & Smith:
iD = knvDS
�
vOV −1
2vDS
�
Which is the same for vS = 0 and n = 1For vDS << VOV (1st order Taylor expansion aroundvDS = 0):
iD = knvOVvDS⇒ gDS = knvOVExcerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 18
weak inversion, triode region
EKV:iD = e
vOVnVT
�
e−vSVT − e
−vDVT
�
For vS = 0:
iD = evOVnVT
�
1− e−vDVT
�
For vDS << VOV (1st order Taylor expansion aroundvDS = 0):
iD = evOVnVT
VD
VT⇒ gDS = e
vOVnVT
1
VT
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 19
Illustration ID vs VGS
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 20
Content
CMOS FET Large Signal Models (book 5.1-5.2)
MOSFET circuits at DC (book 5.3)
Further Model Refinements (book 5.4, will be discussedlater)
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 21
Diode Connected Transistor
In strong inversion:
i =1
2kn(v − Vtn)2
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 22
Simple Current Mirror
When will Iout = Iin, Iout 6= Iin, Iout ≈ Iin, Iout ≈ xIin?Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 23
Content
CMOS FET Large Signal Models (book 5.1-5.2)
MOSFET circuits at DC (book 5.3)
Further Model Refinements (book 5.4, will be discussedlater)
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 24