Previous blogs in this series have covered selection tools for ADCs and DACs. This blog will dig a bit deeper into evaluation using Active Functional Models for ADCs. Analog-to-digital converters are complicated creatures. While we can simplify them for basic functionality and parametric selection, they tend to have a variety of sample rates, gains, and modes. More modern products may have complete configurable analog front-end circuits (AFE), plus digital features including configurable averaging filters, offset and gain adjustment, and FIFO. The analog-centric models must be augmented with reconfigurability to recognize and properly evaluate differences in behavior. Active Functional Models (AFM) do exactly this. These models allow a user to specify selectable configurations, much as will be done in a real system, and then examine the performance. In addition, AFMs give information about onboard digital functions and I/O timing in a simple graphical format.
The first step is to find a product. The prior blogs in this series address that process. Once a product is identified and evaluated at a high level for suitability, it is necessary to look at more detail. This is the point where evaluation begins, though for many applications, it may have already been effectively completed in prior steps. Looking at a landing page for AD7606, the AD7606 Family Software Model is listed under Tools and Simulations. Clicking the link will download an executable file (.exe).
Figure 1: Finding an AFM
Running the executable will launch the installer, which will allow the Active Functional Model to run on your local computer. This is the first tool in this series that does not run on Analog’s web page but runs locally.
The Software Model is designed to allow a user to easily, and virtually, configure a product for use in each application. It is not designed to interface with AFEs and show system performance. Instead, it shows how the ADC will perform in terms of key performance parameters, plus specify digital signaling characteristics, in its various configurations.
Here the configuration screen is shown with the AC Response tab active. At the left are two configuration columns, Config A and Config B which may be used to compare two different configurations of the same ADC, or two different family members of this ADC family. AD7606C and AD7606B are shown in this comparison. Available information tabs include Input Signal (to show the virtual input), Frequency Response, Phase Delay, Time Domain, Step Response, Timing Diagram, DC Histogram, Open Detect, and CRC. Each is easily selected and gives a wealth of useful information.
Figure 2: AFM GUI
Outputs may include Step Response plots, or plots of digital signaling, as below. Each is labeled for configuration, and the actual configurations A and B are always shown graphically.
Figure 3: AFM Outputs
As with the prior tools, the GUI is graphical and includes easy-to-populate text fields for the configuration of the ADC and the signal characteristics. In addition, a register map is included. This makes configuration simple but also gives an easy output to firmware engineers via a memory map that can be saved and exported.
The Software Model gives the user a potent but simple tool to explore the characteristics of an ADC in detail. It requires a low commitment of time or effort, which translates to faster and more effective design. This information is all available in a datasheet but is more easily connected to the design process in this interactive environment. The result of time spent with this tool is a better understanding of the ADC’s capabilities and an optimized configuration and register map that can be used to write control software well before PC board implementation. This allows the system software design to move forward while sensors, AFE, and other circuit elements are still in analog design or evaluation. Finally, the Software Model can work in conjunction with Analog Devices’ ACE plugin Eval Board platform. Future models will be included in the ACE environment for a unified software/hardware evaluation environment.
In addition, junior engineers will find the Software Model helpful for understanding the basics of how a converter works. The ability to look at results relative to sample rate, input amplitude and frequency, dynamic range, antialias filter characteristics, and more, is highly educational. The graphical nature of the tool helps build an intuitive understanding of all converters, as well as the product under investigation.
The next blog post will introduce simulation via LTspice®, which allows for a more complete evaluation of an exact system design.
