Spectre Tech Tips: Dynamic Power Density Circuit Check

Device and circuit reliability heavily depend on how much power is consumed by the individual MOSFET devices and how much heat is generated in a short period of time. To ensure improved reliability and lifetime, circuit designers need to optimize the power consumption of devices in the given design. Starting with Spectre 21.1 ISR10, the circuit simulator provides a new transient-based approach to identify MOSFET devices with large power density values. This dynamic design check is called the dynamic power density check. The details of this check are explained below.

Consider the following power waveform (green) for MOSFET X1.mp1 over a transient period:

The dynamic power density check uses the sliding window approach to locate a time region where the MOSFET has the maximum average power density.

Consider that you want to run the check between the time window from 5n to 20n (grey area in the figure below). This can be set by the parameter time_window. This parameter is optional, and its default value is from the start to the end of transient analysis.

Next, you must set the width of a measuring window for the average power calculation. This can be set by parameter window. There can be multiple measuring windows, where each measuring window is shifted (or slided) by a value set by parameter shift.

Consider that the parameters are set as time_window=[5n 20n], window=10n, and shift=1n. There will be six measuring windows with a width of 10ns each, as shown below.

Each measuring window is shifted by 1ns.

Measuring window 1 = [5ns to 15ns]

Measuring window 2 = [6ns to 16ns]

Measuring window 3 = [7ns to 17ns]

Measuring window 4 = [8ns to 18ns]

Measuring window 5 = [9ns to 19ns]

Measuring window 6 = [10ns to 20ns]

The average power is calculated in each measuring window. For example, the average power of X1.mp1 between 5ns to 15ns is 20e^-6 W and its average power between 10ns to 20ns is 50e^-6 W.

Only the maximum average power (50e^-6 W) and its corresponding measuring window (10n to 20n) is reported by the check.

The maximum average power density is equal to the maximum average power divided by the width of a MOSFET.

By using the above report, you will know that the maximum average power density for device X1.mp1 lies in the 10n to 20n time window.

Related Resources 

Spectre Circuit Simulator Reference

You may also contact your Cadence support AE for guidance.

For more information on Cadence products and services, visit www.cadence.com.

Amaninder Saini

About Spectre Tech Tips

Spectre Tech Tips is a blog series aimed at exploring the capabilities and potential of Spectre^® circuit simulator. In addition to providing insight into the useful features and enhancements in Spectre, this series broadcasts the voice of different bloggers and experts, who share their knowledge and experience on all things related to Spectre. Enter your email address in the Subscriptions box and click SUBSCRIBE to receive notifications about our latest blog posts.