# Mentor Blogs

28 Jan, 2013
System Modeling

## VHDL-AMS Stress Modeling - Part 2

Posted by Mike Jensen

In

Part 1

of this series I started work on a simple resistor model as a way to illustrate some of the flexibility the VHDL-AMS language offers when creating simulation models. Recall that one of the advantages of VHDL-AMS is adding detail to models – a benefit not available with all modeling languages or methods. With VHDL-AMS, it’s possible to get your model and simulator to report performance details not available with other tools. To illustrate this flexibility, my resistor model will include a power dissipation calculation, and a comparison of the result with a user defined power limit to determine stress conditions.

Before jumping into the next model piece, however, I’ll tie up a loose end I left dangling in my earlier post. I mentioned the use of “==” when formulating device equations in a VHDL-AMS model. And at that time I said to simply interpret the syntax as “equal to”. But that definition doesn’t quite cover what’s going on inside the simulator. The “==” is more accurately interpreted as “balance both sides of the equation”. Once the simulator generates a matrix of equations that represent the system, the unknowns are adjusted during simulation, through a series of iterations, until all equations are solved within a user defined accuracy.

Now back to my resistor model. I’m going to jump right into the next architecture, so if you need a review (or a preview) of the model so far, take a quick look at Part 1. Up to this point it’s a basic Ohm’s Law-based resistor: voltage across the resistor is directly proportional to the product of the current and resistance. Now it’s time to add commands to calculate the power.

Recall once again from your first physics or electric circuits class that the power dissipated in a resistor is dependent on any two of its three operating parameters: voltage, current, resistance. There are a few different combinations of these parameters that calculate power, but I’ll use the following:

power = voltage x current

Based on this equation, here is the next section in my model:

1: architecture power1 of resistor is

2: quantity vres across ires through p1 to p2;

3: quantity pwr : power;

4: begin

5: vres == ires*res;

6: pwr == v*i;

7: end architecture power1;

Here I’ve created a new architecture named “power1” for the resistor model. This architecture is the same as the “basic” architecture in my earlier post, except that its name is changed and Lines 3 and 6 are added to setup the power calculation. Line 3 defines a new quantity named “pwr” (remember that a quantity is an analog element in a model) with an assigned VHDL-AMS type of “power”. Note that pwr is not directly associated with the p1 and p2 ports of the model. Therefore the type assignment simply determines what units will be used (in this case “watts”) to plot the pwr quantity. Line 6 calculates pwr as the product of the voltage across the resistor and the current through it, as define in the standard power equation above. This architecture can be added to the model in Part 1 to create a resistor model with one entity and two architectures (recall that a VHDL-AMS model can only have one entity, but multiple architectures). When I use the resistor model in a SystemVision schematic, I can select which architecture to use for that resistor instance. If I choose the power1 architecture, the resistor’s power is calculated at each time or frequency step during the simulation, and becomes a waveform I can plot when the simulation is finished.

Now that my basic resistor is complete, I can add details that will determine if the power exceeds a user defined power rating. In Part 3 of this series I’ll create another new architecture that detects when the resistor’s power exceeds a user defined limit, and notifies me when there is a problem.

29 Oct, 2012
System Modeling

## Preserving Expertise

Posted by Mike Jensen

Like many youth since time began and there were pianos to play, my daughter takes piano lessons. In musical ways, she is much like her mom. Both play piano and sing beautifully. And like her mom, my daughter’s talent is several notches above average, at the level that leaves you wanting to hear more when each piece is over. I recently attended a recital to listen to my daughter and her fellow … Read More

7 Aug, 2012
System Modeling

## Tsunami Remnants

Posted by Mike Jensen

I’m back at my keyboard after a brief, but enjoyable, vacation. Like last year, I trekked with my family to the Oregon Coast. Yes, we enjoy time at the beach, though this time we travelled with extended family so we spent a bit more time driving around site seeing than playing in the tide. In seven days I personally logged some 1200 miles in the driver’s seat. Luckily I don’t mind … Read More

30 Mar, 2012
System Modeling

## Analog Modeling - Part 6

Posted by Mike Jensen

In Part 5 of this series we used the mathematical descriptions of the thermal and electrical properties of an incandescent lamp to create the architecture of a VHDL-AMS-based simulation model. Now it’s time to finish the model, and this blog series, by creating a VHDL-AMS entity for the lamp model. As I mentioned in Part 5, the VHDL-AMS entity defines how a model connects to other elements in a system, … Read More

23 Mar, 2012
System Modeling

## Analog Modeling - Part 5

Posted by Mike Jensen

If you’ve followed this Analog Modeling series, you know we’ve been talking about a general process for HDL-based modeling of analog behavior. If you’re new to the discussion, or simply want to review what we’ve talked about so far, check these links: Part 1, Part 2, Part 3, Part 4. In my last post we developed a set of equations describing the relationship between the thermal … Read More

2 Mar, 2012
System Modeling

## Analog Modeling - Part 4

Posted by Mike Jensen

It’s time to dig a little deeper into the incandescent lamp behavior I introduced in Part 3 of this blog series. My goal is to select a set of equations that best describe the elements of the lamp’s behavior that I want to quantify during simulation. Recall my comment in Part 3 that a lamp has several characteristics worth analyzing including electrical properties, thermal properties, aging … Read More

10 Feb, 2012
System Modeling

## Analog Modeling - Part 3

Posted by Mike Jensen

Welcome to the third installment in my Analog Modeling blog series. In Part 1 I wrote about why equations are important for simulation. In Part 2 I suggested a process flow for turning device equations into a simulation model, and introduced the basic structure of a VHDL-AMS model. Now it’s time to begin the model definition process. As I outlined in Part 2, the first step is deciding what you want … Read More

2 Feb, 2012
System Modeling

## Analog Modeling - Part 2

Posted by Mike Jensen

In Analog Modeling – Part 1 I reviewed the importance of equation selection in the analog modeling process. In a nutshell, the first step in getting good simulation results is choosing equations that best describe the behavior or device you want to analyze. Your analog equation set could be as simple as a single transfer function describing the relationship between the inputs and outputs of a … Read More

25 Jan, 2012
System Modeling

## Analog Modeling - Part 1

Posted by Mike Jensen

I recently spent some time rummaging around my basement. I suppose my basement is not unlike many others — it’s kind of my family’s catch-all storage place for items too big to fit in a closet. Besides housing my HVAC and water heating systems, my basement is home to a variety of holiday decorations, lots of canned, bottled, and bulk food items, a small collection of mismatched folding tables … Read More

2 Dec, 2011
System Modeling

## Analyzing the Big Picture

Posted by Mike Jensen

As engineers we often use “system” to describe different levels of design abstraction. Chip designers refer to integrated circuits as systems on chips. Audio designers refer to an amplifier as a system. Aircraft brake designers create systems for stopping aircraft. There truly are a variety of ways to define and implement a system. And most things we call a system are really just a subsystem … Read More

12 Oct, 2011
System Modeling

## VHDL-AMS Model Portability -- Fact or Fiction?

Posted by Mike Jensen

Once in awhile I work with customers who want to move VHDL-AMS models between multiple simulators. The ability to do so is one of the great promises of standard modeling languages and, at face value, should be an easy task. After all, if a language is an industry standard, and multiple simulation tools claim to support it, then moving models between tools should be a plug-and-play process, right? Well, … Read More

22 Aug, 2011
System Modeling

## Qualities of VHDL-AMS Quantities

Posted by Mike Jensen

One of the most important things I’ve learned during my 20+ years working with simulation tools is simply this: my simulation results will only be as good as my models. While not a revolutionary concept, it’s none the less a fact of system simulation that anyone using a simulator in their design process knows. But there is an equally important companion principle: my model will only give me the … Read More

16 May, 2011
System Modeling

## Integrated System Design

Posted by Mike Jensen

All EDA companies share a common business objective: convincing customers to buy their tools over the competition. Among other marketing tasks, we search for graphics that best express the value of our tools, graphics that customers can look at and immediately understand. Having worked on many charts and graphs myself over the years, I’ll admit it’s not an easy job to find or develop just the right

7 Feb, 2011
System Modeling

## Ideas in Motion

Posted by Mike Jensen

In May 2010 I wrote about a couple of personal transport projects in a post titled Segway to U3-X. Naturally, the Segway Personal Transport (PT) is in production with a variety of options and models. Honda’s U3-X, though cool and seemingly quite practical, as far as I know has yet to see a showroom floor. Perhaps the U3-X was just a platform for Honda’s engineers to research mobility possibilities. … Read More

3 Sep, 2010
System Modeling

## Do You Trust Your Simulator?

Posted by Mike Jensen

Admittedly, I’m a bit biased. After 20+ years in the EDA industry, I’ve developed increasing confidence in modern simulation technology. In short, I generally believe what SystemVision tells me about the systems I analyze. With the right models and simulation settings, I am confident my simulation results will closely match lab measurements on prototype hardware. Part of building confidence is simply … Read More