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Posts tagged with 'Modeling'

25 Mar, 2014
System Modeling

Engineering Oops!

Posted by Mike Jensen

Mike Jensen Awhile back I wrote about the importance and joy of design practice. In that post I suggested that everytime we design something, we are practicing and improving our design skills. And while we do learn from our successful designs, we no doubt learn more from the failures that sometimes litter the path to a project success. If you have done any design practice at all, you have no doubt had a design … Read More

Modeling

21 Jan, 2014

Mike Jensen I wrote a month or so ago about the challenge of finding — or creating — simulation models. In that post, I suggested there are three general categories of engineers looking for a model: Give me a model Help me understand the model Help me develop a model For the “help me develop a model” category, I mentioned Graphical Modeling and Language-based Modeling as two popular model … Read More

modeling tools, Modeling, SPICE

10 Dec, 2013

Mike Jensen Many of my recent interactions with customers have been on a single theme: modeling. Simulation is a great tool, but only if you have models that tell the simulator what to do. Models vary in type and complexity, but they all share a common purpose: to tell you something about how a device or system works, often in a specific application or under specific operating conditions. But there is a gap, an … Read More

SPICE, Modeling

21 May, 2013

Mike Jensen I have written a time or two about my daughter’s piano recitals. As luck would have it, springtime is yet another popular recital season. This time my daughter had two – one for her own piano teacher’s studio, and the other as an invited duet accompanist to play in a friend’s recital. All-in-all, not a bad way to spend a mid-spring evening. As I listened to students play their prepared pieces, I noticed … Read More

Modeling, Mechatronics

25 Mar, 2013

Mike Jensen I’ve been away from my blog for a couple of months helping the SystemVision Engineering team with a few details related to our upcoming release: SystemVision 5.10. We’re excited about this new release. It introduces, among other things, a new way to create simulation models from a variety of data sources. We think this new capability will make it much easier to create SystemVision simulation models. … Read More

Modeling

28 Jan, 2013

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.

Read More

Modeling

29 Oct, 2012
System Modeling

Preserving Expertise

Posted by Mike Jensen

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

Modeling

7 Aug, 2012
System Modeling

Tsunami Remnants

Posted by Mike Jensen

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

Modeling

30 Mar, 2012

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

HDL, Modeling, analog modeling

23 Mar, 2012

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

HDL, analog modeling, Modeling

2 Mar, 2012

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

vhdl-ams training, HDL, analog modeling, Modeling

10 Feb, 2012

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

HDL, analog modeling, Modeling

2 Feb, 2012

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

HDL, Modeling, analog modeling

25 Jan, 2012

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

Modeling, analog modeling

2 Dec, 2011

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

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