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This version (08 Jun 2016 18:00) was approved by TomMac.The Previously approved version (03 Aug 2015 20:42) is available.Diff

ADIsimADC and ADIsimDAC

ADIsimADC™ and ADIsimDAC™ are brand names for a behavioral modeling simulator developed by Analog Devices. The internal name is MOTIF. The following document describes in detail what MOTIF is and how to use it.

What is MOTIF

MOTIF (Modeling Operation Through the Implementation of Features) is a behavioral modeling simulator developed by Analog Devices. We developed MOTIF with two main objectives in mind:

  1. Create a solution to a certain class of simulation problems that were either difficult or intractable through existing technologies
  2. Architect this technology to make it as accessible a possible

All modeling is an exercise in abstraction. We identify which aspects are most important to us and we develop a language around that. SPICE focuses on the flow of electricity through circuits. IBIS focuses on interface boundaries and loading effects. MOTIF, in distinction, focuses on the operation of a device or circuit by identifying and implementing features that are most conspicuous or interesting.

That sounds sufficiently nebulous and vague. Can you explain what you mean by operation? Feature? Conspicuous or interesting?” Yes. We will address each of these in turn.

By operation we mean the natural response of a device or circuit to an input stimulus over time. An example is how an analog-to-digital converter converts from voltage to code at some sampling frequency. Another is convolving a digital sequence of words with the latent impulse response of a Sinc filter. You might want to see the effect of increasing the Sinc order to your reconstructed signal which, by definition, is modeling how that device or circuit operates. If we were being more precise with our language, MOTIF is more of an operational simulator than a behavioral simulator.

By feature we mean some abstract merit that people would consider worthy of notice. An example might be an amplifier’s response to a change in gain. Another is the noise spectral density of a digital-to-analog converter as fOUT changes. Yet another is an exploration of the signal processing capabilities available on some of our analog-to-digital converters.

By conspicuous or interesting we are qualifying the above notion of “worthy of notice.” Not all features are worth the effort to be modeled. For example, whether the data format is Offset Binary or Two’s Complement. Or whether a device is a dual- or quad-channel. Or whether the physical data interface is LVDS or JESD204B. While these are features of the device or circuit of interest, we have deemed that they do not provide sufficient value when modeling operation. This is arbitrary, but as stated above every model is an exercise in abstraction. These same decisions are made when authoring a new SPICE model. By and large all MOTIF models ADI produces lie at approximately the same level abstraction. We strongly feel that there is room for MOTIF to complement, not compete, with existing simulation technologies.

So what problems do MOTIF help to solve that we could not before?” The area of interest that we have focused on is modeling mixed-signal devices. Analog-to-digital and digital-to-analog converters are difficult to model well in SPICE. If you do have a SPICE model of a converter, the required computing power for acquiring meaningful results are both cost and time prohibitive. And this says nothing of the impressive signal processing that continues to be added to our converters, for which SPICE is especially ill-suited.

Why not just make models in ADS? Or Simulink? Or Verilog-AMS? Or VSS? Or XSPICE?[listed in alphabetical order as to not show preference, nor is it exhaustive] This speaks to the second objective of MOTIF which is an emphasis on accessibility. It takes time and resources to create a model. To justify the cost associated with creating for each new device a native model for every simulation environment is an impossible business proposition. Also, we know that the activation energy required to switch tools is significant, and depreciably lowers the rate of adoption. Our solution was develop a single simulator with an open and documented interface and provide a suite of wrappers to embed within popular external simulators. This approach is the best of both worlds: we write one model and you get to keep your favorite simulator!

Our goal is to enable you innovative opportunities to better do your job through the use of this simulator, whether it be through product selection, training, system design, or algorithm development.

Is MOTIF Accurate

We believe so. Check out Umesh Jayamohan's article on ADC Modeling Tools Speed Up Evaluation. There he compares simulation data with a real bench setup and summarizes his findings.

Here's a comparison between hardware (top) and MOTIF (bottom), FFT (left) and SFDR vs. Power Level (right):  Hardware (top) vs. MOTIF (bottom)

In all fairness, there are things MOTIF cannot do. The models are one-way which is to say that data is passed through without consideration of “what” is connected. You could even place an amplifier after an analog-to-digital converter, but we wouldn't recommend it! These considerations must be kept in mind when using MOTIF.

Test Drive MOTIF Online

If you’re interested to see MOTIF in action, we have good news for you. There is a web interface to let you test drive it right now. Consider it a Virtual Eval experience. There you will be able to run behavioral simulations online. There is no need to download anything. Simply select the product you are interested in evaluating and start simulating. Data is generated, simulated with, transformed, graphed, and analyzed.

If you are intrigued with behavioral simulation and want to download the experience, keep reading. The next section on MOTIF Wrappers will help you migrate your web experience to your own machine.

MOTIF Wrappers

Below is a list of wrappers we have initially developed to embed MOTIF within your workflow. Since the interface to MOTIF is open and documented, all wrapper code lacks proprietary information. We have decided to give our wrappers to the open source community. This is the most efficient vehicle we are aware of to encourage the development, dissemination, and ultimately adoption of MOTIF in the industry. If MOTIF doesn't yet work within your simulator of choice, let us collaborate and make it happen!

ADI VisualAnalog
AWR VSS

tbd

C++

tbd

Resources

API Definition
For a detailed description of how to interface to the shared object, see this section.

AN-737
AN-737 Application Note, How ADIsimADC Models an ADC, provides a description of how behavioral simulation is used to model an ADC.

resources/technical-guides/motif.txt · Last modified: 08 Jun 2016 18:00 by TomMac

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