Power Dissipation in Circuits

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Questions and Answers

What does the internal power dissipation of a Non-linear Power Model (NLPM) primarily depend on?

Input net transition and total output net capacitance (correct)

Frequency of the input signal

Input voltage levels and temperature

Time duration of the input signal

Which of the following statements is true about rise and fall power in NLPM?

They do not depend on the internal power dissipation.

They can be represented using different arcs. (correct)

Rise power and fall power must be identical at all input levels.

Fall power is always greater than rise power.

In the context of static power in CMOS logic gates, which value does the power dissipation depend on?

The number of gates in circuit

The state of the gate (0 or 1) (correct)

The output load capacity

The input frequency level

What format does the NLPM use to represent internal power?

Two-dimensional table Signup and view all the answers

What do the values in the rise_power function represent?

Energy dissipated per transition Signup and view all the answers

What mode captures the response of the fabricated circuit during testing?

Capture Mode Signup and view all the answers

In the MUXED-D Scan Cell, what happens when the SE pin is set to 0?

The value at D is latched Signup and view all the answers

During which mode is the scan input SI latched?

Shift Mode Signup and view all the answers

What does the Q pin in a scan cell function as?

Scan Output Signup and view all the answers

What is the state of the SE pin in Normal and Capture modes?

0 for both modes Signup and view all the answers

What type of power dissipation occurs when a circuit is powered on but not actively computing?

Static Power Dissipation Signup and view all the answers

Which parameter in the switching power dissipation formula represents the frequency of the clock?

f_clk Signup and view all the answers

In dynamic power dissipation, what does the term $\alpha$ represent?

Signal activity Signup and view all the answers

What is the formula for calculating the energy dissipated in one cycle of transition from 0 to 1?

$E_{sw} = \frac{1}{2} C_L V_{DD}$ Signup and view all the answers

Which of the following is NOT a type of power dissipation mentioned?

Thermal Power Dissipation Signup and view all the answers

What happens to dynamic power dissipation when a circuit performs computation actively?

It increases due to switching Signup and view all the answers

Which parameter is NOT part of the total power dissipation equation?

Resistance of the circuit Signup and view all the answers

Which component is included in the formula for switching power dissipation?

Capacitance Signup and view all the answers

What is the leakage power value when both signals A and B are high?

300 Signup and view all the answers

What primarily defines the occurrence of static power dissipation?

Circuit being powered on with no active computation Signup and view all the answers

The total power dissipation can primarily be affected by which of the following factors?

Supply voltage ($V_{DD}$) Signup and view all the answers

In the context of VLSI, what does the parameter $\alpha$ represent?

Signal activity Signup and view all the answers

Which statement correctly describes how the activity of a signal can vary?

It is influenced by the logical structure and circuit topology. Signup and view all the answers

Which of the following describes the vector-based technique for estimating activity?

It requires simulation using a test bench. Signup and view all the answers

What is the leakage power value for the condition when A is high and B is low?

150 Signup and view all the answers

What does the symbol $I_{SC}$ represent in power dissipation equations?

Static current Signup and view all the answers

What is the primary purpose of scan configuration during scan synthesis?

To decide the number of scan chains and which elements to convert Signup and view all the answers

Which of the following tasks is involved in scan verification?

Verify the scan shift/capture operation using a logic simulator Signup and view all the answers

What is a common cost associated with scan design flow regarding area overhead?

Costs due to the use of scan cells and routing resources Signup and view all the answers

During which phase of the scan design flow does scan reordering and stitching occur?

Physical design Signup and view all the answers

What is a drawback of integrating multiplexors within the scan design flow?

Performance degradation due to added delay Signup and view all the answers

Study Notes

Overview

Power dissipation broadly consists of two components: dynamic power dissipation, and static power dissipation.
Dynamic power dissipation occurs when a circuit actively computes.
Static power dissipation occurs when the circuit is powered on, but not actively computing.

Dynamic Power Dissipation

Dynamic power dissipation is also referred to as switching power.
The formula to calculate switching power in a synchronous circuit is: 𝑃𝑠𝑤 = 𝐶𝐿 𝑉𝐷𝐷 𝛼𝑓𝑐𝑙𝑘, where:
- 𝑓𝑐𝑙𝑘 = frequency of the clock in the circuit
- 𝛼 = activity of the signal
- 𝐶𝐿 = load capacitance
- 𝑉𝐷𝐷 = supply voltage
The energy dissipated during one cycle of 0→1→0 transition is: 𝐸𝑠𝑤 = 𝐶𝐿 𝑉𝐷𝐷

Non-Linear Power Model (NLPM)

Internal power dissipation depends on the output load and input slew.
It is modeled as a two-dimensional table, referred to as the Non-linear Power Model (NLPM), representing the internal power dissipation.
The table represents energy dissipation per transition as dependent on the output load and input slew.

Technology Library Models: Static Power

Static power dissipated inside a CMOS logic gate depends on the value (0 or 1) at its input pin.
It can be modeled using a when condition in the library, with a value representing the static power dissipation for different input pin values.

Estimating Power Dissipation

The total power dissipation can be calculated using the following formula: 𝑃𝑡𝑜𝑡 = 𝐶𝐿 𝑉𝐷𝐷 𝛼𝑓𝑐𝑙𝑘 + 𝑉𝐷𝐷 𝐼𝑆𝐶 + 𝑉𝐷𝐷 𝐼𝑙𝑒𝑎𝑘, where:
- 𝑉𝐷𝐷 = supply voltage
- 𝐶𝐿 = load capacitance
- 𝑓𝑐𝑙𝑘 = frequency of the clock in the circuit
- 𝛼 = activity of the signal
- 𝐼𝑆𝐶 = short circuit current
- 𝐼𝑙𝑒𝑎𝑘 = leakage current

Estimation of Activity

Activity of a signal depends on the application and the circuit's logical structure and topology.
Simulation-based techniques (Vector-based Technique) rely on test benches to estimate activity.

Scan Cells

Scan cells are used for testing.
They are typically multiplexer-based D flip-flops with scan input (SI), scan enable (SE), and scan output (SO) pins.
Most popular is the MUXED-D Scan Cell.
During normal/capture mode, SE=0 and the value at D is latched.
In shift mode, SE=1 and the SI value is latched.
Output pin produces the content of the D flip-flop.

Scan Design Flow: Tasks

Design Preparation: Ensures the design is testable.
Scan Synthesis: Converts the design into a scan design.
- Scan Configuration: Decides on the number of scan chains, scan cells, and excludes elements from being converted to scan cells.
- Scan Replacement: Replaces flip-flops with scan cells.
- Scan Reordering and Stitching: Reorders scan cells based on physical location to facilitate easier routing.
Test Vector Generation: Generates test vectors.
Scan Verification: Verifies scan shift/capture operation and timing (STA).

Scan Design Flow: Costs

Area Overhead: Scan cells and routing resources contribute to area overhead.
IO Pin Cost: Increased IO pins are required.
Performance Degradation: The multiplexer adds delay, leading to performance degradation.
Design Effort Cost: Increased design effort is required for scan design.

OpenSTA Tutorial: Power Analysis

OpenSTA is a tool for power analysis.
Tutorial 9 of the course explores the power analysis using OpenSTA tool.
OpenSTA installation and usage information is detailed in Tutorial 7.

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Description

This quiz covers key concepts of power dissipation in electronic circuits, focusing on dynamic and static power. You will learn about the formulas for calculating switching power and the Non-Linear Power Model as it relates to internal power dissipation. Prepare to test your understanding of these critical elements in circuit design.