Podcast
Questions and Answers
What is the total power dissipation in CMOS circuits comprised of?
What is the total power dissipation in CMOS circuits comprised of?
- Pdyn plus Pstat (correct)
- Psw plus Psc
- Pdyn only
- Pstat only
Which component of power dissipation accounts for unnecessary transitions in the output?
Which component of power dissipation accounts for unnecessary transitions in the output?
- Static power dissipation
- Glitches (correct)
- Short-circuit power dissipation
- Leakage power dissipation
What does the equation Psw = CL V²DD fCLK α represent?
What does the equation Psw = CL V²DD fCLK α represent?
- Leakage power dissipation
- Total power dissipation
- Static power dissipation
- Switching power dissipation (correct)
Which factor does NOT affect switching power dissipation in CMOS circuits?
Which factor does NOT affect switching power dissipation in CMOS circuits?
What form of energy is dissipated during the output rising transition in a CMOS inverter?
What form of energy is dissipated during the output rising transition in a CMOS inverter?
In the context of power dissipation, what does 'Pdyn' refer to?
In the context of power dissipation, what does 'Pdyn' refer to?
What happens to the total power dissipation as supply voltage is reduced in CMOS technology?
What happens to the total power dissipation as supply voltage is reduced in CMOS technology?
Which statement accurately describes static power dissipation in CMOS circuits?
Which statement accurately describes static power dissipation in CMOS circuits?
What causes glitches in dynamic gates?
What causes glitches in dynamic gates?
Which of the following represents the total power dissipation in a circuit?
Which of the following represents the total power dissipation in a circuit?
How is short-circuit power (Psc) affected by transistor size?
How is short-circuit power (Psc) affected by transistor size?
What condition must be satisfied to prevent short-circuit power consumption in a CMOS gate?
What condition must be satisfied to prevent short-circuit power consumption in a CMOS gate?
What effect does load capacitance (CL) have on peak short circuit current?
What effect does load capacitance (CL) have on peak short circuit current?
Which of the following components of power is NOT included in dynamic power?
Which of the following components of power is NOT included in dynamic power?
Subthreshold leakage current, Isub, dominates in which condition?
Subthreshold leakage current, Isub, dominates in which condition?
What is a primary cause for an increase in short-circuit power during a transition?
What is a primary cause for an increase in short-circuit power during a transition?
Which leakage component is due to tunneling at the gate-drain overlap?
Which leakage component is due to tunneling at the gate-drain overlap?
What condition is necessary to completely eliminate short-circuit power?
What condition is necessary to completely eliminate short-circuit power?
What happens to short-circuit power when the gate output transition is faster than the input transition?
What happens to short-circuit power when the gate output transition is faster than the input transition?
What type of leakage current becomes significant with scaling due to thin oxide layers?
What type of leakage current becomes significant with scaling due to thin oxide layers?
What approximates the energy drawn during a glitch in a dynamic gate?
What approximates the energy drawn during a glitch in a dynamic gate?
Which condition is necessary for short-circuit conduction to occur in a CMOS gate?
Which condition is necessary for short-circuit conduction to occur in a CMOS gate?
Which of the following is NOT a component of leakage current?
Which of the following is NOT a component of leakage current?
What is the effect of a low threshold voltage (VTH) on subthreshold leakage current?
What is the effect of a low threshold voltage (VTH) on subthreshold leakage current?
Flashcards
CMOS Inverter Power Dissipation
CMOS Inverter Power Dissipation
Power consumed by a CMOS inverter, categorized into dynamic and static components
Dynamic Power (Pdyn)
Dynamic Power (Pdyn)
Power consumed during switching actions in a CMOS circuit, including that used by switching and glitches.
Switching Power (Psw)
Switching Power (Psw)
Component of dynamic power dissipation related to logic activity, directly proportional to capacitance, voltage squared, and frequency
Capacitance (CL)
Capacitance (CL)
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Supply Voltage (VDD)
Supply Voltage (VDD)
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Frequency (fCLK)
Frequency (fCLK)
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Glitches
Glitches
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Static Power (Pstat)
Static Power (Pstat)
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Dynamic Gate Glitch
Dynamic Gate Glitch
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Glitch Power Dissipation
Glitch Power Dissipation
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Dynamic Power Component (Pdyn)
Dynamic Power Component (Pdyn)
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Short-Circuit Power (Psc)
Short-Circuit Power (Psc)
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Peak Short-Circuit Current
Peak Short-Circuit Current
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Short-circuit power reduction
Short-circuit power reduction
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VDD Scaling
VDD Scaling
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Total Power Dissipation
Total Power Dissipation
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CMOS gate short-circuit power
CMOS gate short-circuit power
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Short-circuit conduction
Short-circuit conduction
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Dynamic Power
Dynamic Power
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Static Power
Static Power
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Subthreshold Leakage
Subthreshold Leakage
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Gate-induced drain leakage (IGIDL)
Gate-induced drain leakage (IGIDL)
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Leakage Current Components
Leakage Current Components
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Dynamic Power Components
Dynamic Power Components
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Study Notes
Power Dissipation in CMOS
- CMOS logic (inverter) has no static leakage path for either 1 or 0 inputs.
- Power dissipation consists of dynamic and static components.
- Dynamic Component (Pdyn): Switching power (Psw), logic activity, and glitches.
- Short-circuit power (Psc).
- Static Component (Pstat): Leakage power.
- Total power (Ptotal) = Pdyn + Pstat = (Psw + Psc) + Pstat
Switching Power (Psw)
- Defined as the power consumed when charging and discharging the load capacitance (CL) with the supply voltage (VDD) during a switching cycle (T).
- Psw = CL VDD2 / T
- Switching power depends on capacitance, supply voltage, clock frequency, and activity factor.
Glitches
- Temporary changes in the output value (unnecessary transitions).
- Caused by skew in input signals to a gate.
Type of Logic Function
- Static 2-input NOR gate: Transition probability (0→1) = 3/16
- Static 2-input XOR gate: Transition probability (0→1) = 1/4
Dynamic Gate
- Dynamic gates consume power during pre-charge and evaluation phases of the clock cycle (CLK waveform).
Dynamic Power Consumption
- Dynamic power consumption is data-dependent.
- Logic functions with higher transitions have higher activity factors which in turn, leads to higher power consumption in dynamic gates.
Glitch Power Dissipation
- Glitch power dissipation depends on the voltage swing of incomplete transitions within a clock cycle.
- Formula for approximating glitch power: Pglitch = (1/T) * Cload * VDD * ΣΔVn
Short-Circuit Power (Psc)
- Power dissipation during the transition period when both the NMOS and PMOS transistors are partially ON simultaneously.
- Psc = Imean * VDD
- Short-circuit power increases with transistor size, input transition time, and decreases with load capacitance.
Leakage Power
- Leakage power is the continuous power consumption due to various leakage components like:
- Subthreshold leakage (Isub)
- Reverse bias pn junction leakage (ID)
- Gate-induced drain leakage (IGIDL)
- Drain-source punch-through (Ipt)
- Gate tunneling (IG)
Subthreshold Leakage (Isub)
- Occurs when the gate-source voltage (VGS) is less than the threshold voltage (VTH).
- Dominated by diffusion current.
- Most important OFF-state leakage mechanism in modern CMOS devices.
- Formula for subthreshold leakage in long-channel devices: Isub = μ0 Cox (W/L) VT2 exp{(VGS - VTH)/ηVT}
CMOS Gate and Short-Circuit Power
- A CMOS gate consumes no short-circuit power when the supply voltage (VDD) is less than or equal to the sum of the threshold voltages of the nMOS and pMOS transistors (VDD ≤ Vtn + |Vtp|).
- The short-circuit power occurs when both transistors are ON simultaneously during the input transition.
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Description
This quiz explores the fundamentals of power dissipation in CMOS circuits, covering both dynamic and static components. You'll learn about factors affecting switching power and the significance of glitches in digital logic. Test your understanding of how these concepts contribute to overall power consumption in CMOS technology.
