1. ELEC 301 Volkan Kursun Design Metrics ECE555 - Volkan Kursun

2. Announcements Project is announced
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Announcements
Project is announced
Form a group of two students by March (next Thursday)
Give the names of your group members to the lab technician Alex by March
You cannot modify the group members after March 19
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3. Announcements HW1 solution is on the web HW2: on the web Midterm exam
ECE555 - Volkan Kursun
Announcements
HW1 solution is on the web
HW2: on the web
Midterm exam
Venue: Lecture Theater A
Date: 31 Mar 2009 (Tue)
Time: 18: :00
Closed book exam
No copy sheets
Bring a calculator
ECE555 - Volkan Kursun

4. Representation of Digital Signals
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Representation of Digital Signals
Digital systems perform operations on logical (Boolean) variables
A logical variable can have two discrete values
X: 0, 1
A logical variable is a mathematical abstraction
Physical implementation requires the representation of logical variables with electrical quantities
Voltage
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5. Representation of Digital Signals
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Representation of Digital Signals
Node voltage
Not discrete
Has a continuous range of values
Turn the electrical voltage into a discrete variable by associating a nominal voltage level with each logic state
1: VOH
0: VOL
VOH and VOL represent the nominal high and low logic levels, respectively
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6. Reliability― Noise in Digital Integrated Circuits
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Reliability― Noise in Digital Integrated Circuits v ( t ) V DD i ( t )
Inductive coupling
Capacitive coupling
Power and ground
noise
Noise: unwanted variation of voltage and current at a circuit node
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7. Mapping Between Analog and Digital Signals
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Mapping Between Analog and Digital Signals
Digital circuits can tolerate certain amount of deviations from the nominal voltages
Logic levels are represented by a range of acceptable voltages, rather than only by a nominal voltage
The voltage ranges of logic levels are separated by a region of uncertainty OH OL IH IL V V V V ” ” 1
Undefined
Region “ “
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8. DC Operation Voltage Transfer Characteristics
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DC Operation Voltage Transfer Characteristics
Electrical function of a gate is determined by the voltage transfer characteristics
DC transfer characteristics
Plot the output voltage as a function of the input voltage
Vout = f (Vin)
Determine the acceptable ranges of input and output voltages
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9. DC Operation Voltage Transfer Characteristic
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DC Operation Voltage Transfer Characteristic
Vout
VOH = f(VOL)
VOL = f(VOH)
VM = f(VM) V f OH
Vout = Vin VM
Switching Threshold Voltage V OL V V
Vin OL OH
Nominal Voltage Levels
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10. Mapping Between Analog and Digital Signals
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Mapping Between Analog and Digital Signals
The regions of acceptable high and low voltages are delimited by VIH and VIL V
out V “ 1 ” OH
Slope = -1 V OH V IH
Vin = Vout
Undefined
Gate switching threshold voltage
Region V IL
Slope = -1 V “ ” V OL OL V V V IL IH in
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11. ECE555 - Volkan Kursun
Noise Margins
For a gate to be robust, the acceptable voltage ranges of the “0” and “1” logic levels must be as large as possible
Concept of noise margins
A measure of the tolerance of a gate to noise
Noise margin low (NML)
Quantizes the range of voltages considered valid 0
Noise margin high (NMH)
Quantizes the range of voltages considered valid 1
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12. Definition of Noise Margins
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Definition of Noise Margins
Steady-state signals must avoid the undefined region for a proper operation
Lowest voltage that is considered logic high: “1”
"1" V OH NM
Noise margin high H V IH
Undefined Region NM V
Noise margin low L IL V OL
Highest voltage that is considered logic low: “0”
"0"
Gate Output
Gate Input
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13. Noise Budget Noise sources: supply noise, cross talk, and interference
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Noise Budget
Noise sources: supply noise, cross talk, and interference
Differentiate between static and dynamic noise sources
Static noise budget allocates gross noise margins to expected sources of noise
Static noise margins result in very conservative designs
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14. Regenerative Property
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Regenerative Property
A voltage v0 that deviates from the nominal voltages is applied to the first inverter
The signal gradually converges to one of the nominal values after a number of inverter stages
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15. Signal Regeneration (Restoration)
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Ex: Chain input signal Vo is degraded due to noise → reduced voltage swing v 1 2 3 4 5 6
A chain of inverters
The deviation in voltage levels disappears as the signals propagate through a chain of inverters
Simulated response
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16. Fan-in and Fan-out
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Fan-out: number of loading gates connected to the output of a gate
Fan-in: number of inputs N
Fan-out N M
Fan-in M
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17. Fan-in and Fan-out
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Increasing the fan-out can affect the output logic level
To minimize the effect of fan-out on logic levels
Input resistance of load gates must be as large as possible
Low output current to the fan-out gates
Output resistance of the driver gate must be as small as possible
Reduce the effect of output currents on the output voltage level N
Fan-out N
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18. The Ideal Gate Voltage Transfer Characteristics
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The Ideal Gate Voltage Transfer Characteristics V
out R i = R o
= 0
Fanout = ¥
NMH = NML = VDD/2
g =  V in
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19. An Old-time Inverter: NMOS
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VDD = 5V, VGND = 0V
VOH = 3.5V, VOL = 0.45V, VIH = 2.35V, VIL = 0.66V, VM = 1.64V, NML = 0.21V, NMH = 1.15V NM H V in
(V)
out L M
0.0
1.0
2.0
3.0
4.0
5.0
Issues:
Asymmetrical VTC
Narrow noise margins
Low NML
VOH < VDD
VOL > 0
Low output voltage swing
(VOH - VOL) < VDD
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20. Delay Definitions
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How quickly does a circuit respond to a change of the inputs?
Delay experienced by a signal while propagating through a circuit
Propagation delay is a function of
Technology
GaAs vs. silicon CMOS
Circuit topology
Slopes of the input signals
Load and driver impedances
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21. Delay Definitions High-to-low and low-to-high propagation delays
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High-to-low and low-to-high propagation delays
tp = (tPHL + tPLH) / 2
Rise time: tr
Fall time: tf
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22. Ring Oscillator For oscillation: 2Ntp >> tr+tf T = 2 ´ t N 1 1 1
ECE555 - Volkan Kursun 1 1 1 1 1 1
T = 2 t p N
For oscillation: 2Ntp >> tr+tf
Otherwise the propagating signals overlap and dampen the oscillation
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23. A First-Order RC Network
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A First-Order RC Network v
out in C R
tp = ln (2) t = 0.69 RC
Simplest model to represent the delay of an inverter
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24. Power Dissipation Power: energy dissipated or stored per unit of time
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Power: energy dissipated or stored per unit of time
Influences several design decisions
Power supply
Power distribution network
Nominal supply voltage VDD and tolerable variation
Supply current demand
Battery lifetime
Heat dissipation
Packaging
Cooling system
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25. Power Dissipation
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Limits the number of devices than can be integrated on an IC
Limits how fast a circuit can operate
Faster circuits tend to consume more power
Limits the number of operations that can be performed between battery changes
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26. Power Dissipation Instantaneous power: p(t) = v(t)i(t) = Vsupplyi(t)
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Instantaneous power:
p(t) = v(t)i(t) = Vsupplyi(t)
Peak power:
ppeak = Vsupplyipeak = max [p(t)]
Critical in power supply and distribution network design
Average power:
Critical to determine the cooling and battery requirements
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27. Power – Components
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Dynamic power: Occurs during transients when a circuit is switching
Due to charging of capacitors
+ temporary current paths between the supply rails
Proportional to the switching frequency
The higher the number of switching events the greater the dynamic power consumption
Static power: Occurs statically, all the time, regardless of a switching activity
Caused by the static conduction paths between the supply rails and the leakage currents
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28. Power – Speed Relationship
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Propagation delay is determined by the speed at which a given amount of energy can be transferred to/from the parasitic capacitors of a circuit (C = Q / V)
The faster the energy transfer, the higher the circuit speed is
Faster energy transfer means higher power consumption
Reminder:
Power: energy dissipated or stored per unit of time
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29. A First-Order RC Network
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A First-Order RC Network R v
out v in CL
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30. Energy and Energy-Delay Product
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Energy and Energy-Delay Product
Power-Delay Product (PDP) = Pav  tp
PDP: Energy (E) consumed by a gate per switching event
Energy-Delay Product (EDP) = power x delay2
quality metric of a gate = E  tp
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