# Understanding Component Model Parameters for Electronic Circuit Design

March 5, 2020

While I can’t admit to paying attention to the fashion industry as much as some others, I can confidently say I enjoy watching the fashion shows. I can’t say I understand where, when, or how someone might wear the designs these designers come up with half the time, but it is interesting seeing the twists, gems, and patterns on new lines of clothing.

There are no glamorous runways in electronics design nor models to keep you engaged in your tasks. However, you’ll need to pay attention to getting the component model parameters right before you run any analysis on the circuit. Getting a single value wrong can result in hours of frustration, or worse, making incorrect design decisions.

## What Are Component Model Parameters

In the perfect world, we hope that we can put up a circuit quickly and test it out before having it laid out on a circuit. However, the world isn’t perfect and roughly patching up a circuit is madness when you have hundreds of components in it.

Instead of getting the circuit designed with your best knowledge and hoping that everything goes well after the PCB is made, electronics circuit analysis software is created. Such programs are called SPICE, which stands for Simulation Program with Integrated Circuit Emphasis

For a SPICE program to work, components need to be connected accordingly to the design. The crucial factors that enable SPICE analysis to be performed are the component model parameters. In other words, the components modeled in SPICE need to mimic the behavior of real-life components.

Component model parameters involved are not only limited to the electrical properties but may also involve thermal and physical characteristics. The component models are expressed in a specific netlist syntax for the SPICE program to process. For example, a basic model for the resistor is

R<name> <(+) node> <(-) node> [model name] <value> + [TC = <TC1> [,<TC2>]]

It is visible from the SPICE syntax that not only the value of the resistance is used, but also the length, width, and temperature coefficients of the resistor.  Other types of components have their respective model parameters that reflect their real-world behavior.

## How Component Model Parameters Help Circuit Design

It’s fair to say that electronics design is a complicated affair where even the most experienced designer may overlook some details. A circuit may look good on paper but when the PCBs are made and deployed, multiple issues may appear. Often such issues are related to conditions that are hard to be replicated during prototype testing.

Using SPICE software along with accurate component model parameters provide a good picture of how the circuit will response in specific conditions. SPICE analysis is often used to inspect the DC, AC and transient response of the circuit. Transient analysis, in particular, is useful to identify how the components will respond to sudden changes in voltage or current.

Component model parameters enable SPICE analysis in design.

As the parameters also involved physical and thermal properties, you can also run analysis to determine potential breakpoints when the values are pushed to the limits. Monte Carlo and sensitivity tests also banked on the component parameters to return yield predictions during production.

## Challenges In Mapping Component Model Parameters

Theoretically, using SPICE with the supplied component model parameters is an easy way to test out the circuit. However, you’ll need to have fair control over editing the parameters as most of the pre-built models are based on a specific operating condition. Depending on the SPICE program that you’re using, changing the model parameters can be difficult.

Flexibility in changing component model parameters is key to accurate SPICE Analysis.

It takes a great deal of experience and study to manually edit the netlist of the said component, and it’s easy to make mistakes. The lack of documentation, especially if the model parameters are supplied by the component vendor further complicates matters. It will be pointless to simulate a circuit when the parameters are not configured to the required condition.

No matter what electronics you’re developing, you’ll be sure to need a strong suite of design and analysis tools like those offered by Cadence. Ultimately, you’ll need a SPICE program like PSpice Simulator that allows changes on the component parameters to be made easily.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

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