The first post in this series covered a lot of ground. This post will spotlight two tools in more detail. Let’s dig into those tools and look at the ADC + Driver, which is often the core of a measurement or monitor system design. The selection process should start in the Product Selection Tables at Analog
Figure 1: Finding the Tools
You can find Precision Converter Products here. These tables give a list of products and are searchable by specifications and features. It’s helpful to know that the Product Selection Tables give the option to look for products that have an appropriate model (Figure 2).
Figure 2: How to select products that have models
Once you’ve narrowed down the selection to a few products you’d like to compare, the ADC Driver Tool is the next step. This tool allows you to experiment with ADC and driver combinations quickly and easily. It is appropriate to look at this pair of blocks together, as the ADC driver is required for many products, and each unique combination of ADC + Driver will give different performance and features. It is also helpful to know that many newer Precision ADC products have EasyDrive inputs, which allow for either no driver or minimal buffering ahead of the ADC inputs.
To use the ADC Driver Tool, simply open it up on the Analog webpage here. Select an ADC, and a circuit will display with the chosen ADC and appropriate driver(s) as in Figure 3. Alternative driver amplifiers and AFE circuits may be substituted to optimize the circuit for a given application. The left-side column gives additional variables, including sample rate and input frequency.
Figure 3: ADC Driver Tool GUI
The ADC Driver Tool then provides analysis including noise, distortion, kickback (charge injection disturbance), and settling. The ADC Driver Tool is not just useful for circuit analysis, it is also helpful in understanding the relationship between the ADC and the driver, learning about drive circuits, and familiarizing the user with common methods and problems. It is possible to easily alter the input antialias filter to observe charge kickback and settling behavior as an example. If this analysis is enough to move forward, the ADC Driver Tool will export an LTspice®-compatible netlist for deeper analysis.
The Noise Tool is an Analog-Front-End (AFE) tool that is designed to evaluate a wider range of circuits from sensor-to-bits. It includes more ADC and amplifier models than the ADC Driver Tool and covers a much wider array of AFE circuits and topologies. As it is more comprehensive, the Noise Tool has more flexibility and options, though it still takes little time and effort. The user may choose to build a schematic from scratch or may choose from a variety of example schematics, including Pulsed Light, Precision Waveform, Low-Power Bridge, and others. Once built, the Noise Tool gives information about total system performance and also breaks out errors by component, which is very helpful for optimizing a design. The circuits may include gain stages, drivers, filters, passives, and more. Components may be swapped, and are easily chosen, as the tool allows for block-by-block analysis and optimization in an intuitive graphical format. Simulations are behavioral, so they respond to changes and run extremely quickly.
Figure 4: Noise Tool GUI
Figure 5: Choosing an architecture in Noise Tool
Figure 6: Choosing alternative blocks - optimizing the amplifier
Analog’s Noise Tool will display the transfer function, plus noise spectrum or total noise, at the system stage level. It is quick and easy to change components and configurations to look for an optimal solution. As with the ADC Driver Tool, the Next Steps section will export results and an LTspice-compatible netlist for deeper analysis. The Noise Tool is still in beta at this time. Work is ongoing to add additional analysis capabilities and components. To let us know what you would value, click on the feedback icon in the tool’s upper right corner.
Both the ADC Driver Tool and Noise Tool give immediate feedback on design choices, allowing a system designer to quickly choose components and optimize a design. Results are immediately displayed in a way that makes it easy to understand how choices affect the system's performance. Finally, there is a direct path to LTspice for comprehensive analysis if desired.
In next month’s blog, I’ll discuss choosing a DAC using the DAC Error Budget Tool!
The ADC Driver Tool and Noise Tool are so useful in precision system design. My experience is that, for many designers, ADC driving isn't well understood but the ADC driver tool helps designers make the best choice given their signal bandwidth and SNR requirements. The noise tool offers eye-opening insight into the dominant noise sources in your signal chain, so that you can optimise designs for the best possible SNR, within the bounds of all your other design constraints.