THE INVERTERS
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Transcript of THE INVERTERS
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
THE INVERTERS
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
DIGITAL GATES Fundamental Parameters
Functionality Reliability, Robustness Area Performance
» Speed (delay)» Power Consumption» Energy
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Noise in Digital Integrated Circuits
VDDv(t)
i(t)
(a) Inductive coupling (b) Capacitive coupling (c) Power and ground
noise
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
DC Operation: Voltage Transfer Characteristic
V(x)
V(y)
VOH
VOL
VM
VOHVOL
fV(y)=V(x)
Switching Threshold
Nominal Voltage Levels
V(y)V(x)
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Mapping between analog and digital signals
"1"
"0"
VOH
VIH
VIL
VOL
UndefinedRegion
V(x)
V(y)
VOH
VOL
VIH
VIL
Slope = -1
Slope = -1
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Definition of Noise Margins
VIH
VIL
UndefinedRegion
"1"
"0"
VOH
VOL
NMH
NML
Gate Output Gate Input
Noise Margin High
Noise Margin Low
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
The Regenerative Property
(a) A chain of inverters.
v0, v2, ...
v1, v3, ... v1, v3, ...
v0, v2, ...
(b) Regenerative gate
f(v)
finv(v)
finv(v)
f(v)
(c) Non-regenerative gate
v0 v1 v2 v3 v4 v5 v6
...
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Fan-in and Fan-out
N
M
(a) Fan-out N
(b) Fan-in M
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
The Ideal Gate
Vin
Vout
g=
Ri =
Ro = 0
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
VTC of Real Inverter
0.0 1.0 2.0 3.0 4.0 5.0Vin (V)
1.0
2.0
3.0
4.0
5.0
Vo
ut (V
)
VMNMH
NML
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Delay Definitions
tpHL
tpLH
t
t
Vin
Vout
50%
50%
tr
10%
90%
tf
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Ring Oscillator
v0 v1 v2 v3 v4 v5
v0 v1 v5
T = 2 tp N
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Power Dissipation
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS INVERTER
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
The CMOS Inverter: A First Glance
VDD
Vin Vout
CL
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverters
Polysilicon
InOut
Metal1
VDD
GND
PMOS
NMOS
1.2 m=2
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Switch Model of CMOS Transistor
Ron
|VGS| < |VT||VGS| > |VT|
|VGS|
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverter: Steady State Response
VDD VDD
VoutVout
Vin = VDD Vin = 0
Ron
Ron
VOH = VDD
VOL= 0
VM = Ronp) f(Ronn,
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverter: Transient Response
VDD
Vout
Vin = VDD
Ron
CL
tpHL = f(Ron.CL)
= 0.69 RonCL
t
Vout
VDD
RonCL
1
0.5
ln(0.5)
0.36
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Properties
Full rail-to-rail swing Symmetrical VTC Propagation delay function of load
capacitance and resistance of transistors No static power dissipation Direct path current during switching
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Voltage TransferCharacteristic
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverter VTC
Vout
Vin1 2 3 4 5
12
34
5
NMOS linPMOS off
NMOS satPMOS sat
NMOS offPMOS lin
NMOS satPMOS lin
NMOS linPMOS sat
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Simulated VTC
0.0 1.0 2.0 3.0 4.0 5.0Vin (V)
0.0
2.0
4.0
Vo
ut (V
)
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Gate Switching Threshold
0.1 0.3 1.0 3.2 10.01.0
2.0
3.0
4.0
kp/kn
VM
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
MOS Transistor Small Signal Model
rogmvgsvgs
+
-
S
DG
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Determining VIH and VIL
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Propagation Delay
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverter: Transient Response
VDD
Vout
Vin = VDD
Ron
CL
tpHL = f(Ron.CL)
= 0.69 RonCL
t
Vout
VDD
RonCL
1
0.5
ln(0.5)
0.36
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverter Propagation Delay
VDD
Vout
Vin = VDD
CLIav
tpHL = CL Vswing/2
Iav
CL
kn VDD
~
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Computing the Capacitances
VDD VDD
VinVout
M1
M2
M3
M4Cdb2
Cdb1
Cgd12
Cw
Cg4
Cg3
Vout2
Fanout
Interconnect
VoutVin
CL
SimplifiedModel
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
CMOS Inverters
Polysilicon
InOut
Metal1
VDD
GND
PMOS
NMOS
1.2 m=2
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
The Miller Effect
Vin
M1
Cgd1Vout
V
V
Vin
M1
Vout V
V
2Cgd1
“A capacitor experiencing identical but opposite voltage swings at both its terminals can be replaced by a capacitor to ground, whose value is two times the original value.”
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Computing the Capacitances
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Impact of Rise Time on Delayt p
HL(n
sec
)
0.35
0.3
0.25
0.2
0.15
trise (nsec)10.80.60.40.20
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Delay as a function of VDD
0
4
8
12
16
20
24
28
2.00 4.001.00 5.003.00
Nor
mal
ized
Del
ay
VDD (V)
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Where Does Power Go in CMOS?
• Dynamic Power Consumption
• Short Circuit Currents
• Leakage
Charging and Discharging Capacitors
Short Circuit Path between Supply Rails during Switching
Leaking diodes and transistors
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Dynamic Power Dissipation
Energy/transition = CL * Vdd2
Power = Energy/transition * f = CL * Vdd2 * f
Need to reduce CL, Vdd , and f to reduce power.
Vin Vout
CL
Vdd
Not a function of transistor sizes!
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Impact ofTechnology
Scaling
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Technology Evolution
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Technology Scaling (1)
Minimum Feature Size
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Technology Scaling (2)
Number of components per chip
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Propagation Delay Scaling
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Technology Scaling Models
• Full Scaling (Constant Electrical Field)
• Fixed Voltage Scaling
• General Scaling
ideal model — dimensions and voltage scaletogether by the same factor S
most common model until recently —only dimensions scale, voltages remain constant
most realistic for todays situation —voltages and dimensions scale with different factors
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Scaling Relationships for Long Channel
Devices
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Digital Integrated Circuits © Prentice Hall 1995InverterInverter
Scaling of Short Channel
Devices