INF3410 — Fall 2016
Transcript of INF3410 — Fall 2016
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INF3410 — Fall 2016
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs)
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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
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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
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Device Concept
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 4
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Device Cross Section
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 5
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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
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nFET/NMOS and pFET/PMOS cross section
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 7
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Above Threshold Regions of Operation NFET
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 8
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Above Threshold Regions of Operation PFET
’Above Threshold’ is also called ’Strong Inversion’
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 9
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nMOSFET Device Symbols
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 10
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pMOSFET Device Symbols
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 11
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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
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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
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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
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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
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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
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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
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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
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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
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Illustration ID vs VGS
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 20
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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
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Diode Connected Transistor
In strong inversion:
i =1
2kn(v − Vtn)2
Excerpt of Sedra/Smith Chapter 5: CMOS Field EffectTransistors (FETs) 22
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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
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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