Designing a circuit to capture precision data from a sensor can be a complex juggling act. Each application has a unique set of target specifications and tradeoffs that must be considered. The chosen circuit architecture and interaction between components may introduce unexpected side effects. And, the process of picking components from a myriad of datasheets is filled with back-of-envelope calculations, spreadsheets, spaghetti-wired prototypes, and plenty of uncertainty. 
Typical Design Tools: Datasheets, Spreadsheets, Prototypes
Signal Chain Designer, the latest addition to the Precision Studio suite of design tools, is tailored for navigating the challenges of data acquisition system development. This interactive tool allows designers to drag-and-drop sensor models, analog signal conditioning blocks, ADCs, and digital filters into a signal chain and immediately see the impact of design choices on critical system parameters like SNR, gain and offset error, power, and more.
To begin designing a signal chain, start with one of several examples or build from scratch by selecting a sensor and setting a few simple parameters to model the sensor behavior. After selecting a sensor, creating a signal chain is as easy as dropping circuit blocks into place and specifying the desired function of each block.
Drag-and-drop circuit blocks into signal chain
Typically, amplifier stages are used for signal buffering and amplification, level-shifting, and converting between single-ended and differential signals. Once the stage is placed in the signal chain and the I/O types, gain, and level-shift parameters are specified, Signal Chain Designer generates an appropriate circuit architecture for that function, complete with ADI amplifiers, passives, and voltage references. The tool also gives the flexibility to choose whether to use fully-differential amplifiers, instrumentation amplifiers, or operational amplifiers to implement the signal conditioning, when appropriate.
Configure Amplifier Stage
Amplifier stage schematic generated by Signal Chain Designer
Another common signal conditioning function in precision data acquisition systems is filtering. The Signal Chain Designer offers two methods for implementing analog filters. For simple filters, the behavior can be specified directly in the tool by setting parameters for filter type, f₀, and Q factor. For higher-order filters (or to utilize its powerful design capabilities), the Filter Wizard tool can be invoked directly from the Signal Chain Designer and the filter imported back into the signal chain.
Configure Filter Stage
Filter stage schematic generated by Signal Chain Designer
No data acquisition system would be complete without converting the analog real-world signal into a digital form. The Signal Chain Designer models the performance of many of ADI’s precision SAR and Sigma-Delta ADCs, including several data acquisition μModules. After specifying the input type, resolution, and output data rate, the tool generates an ADC circuit, including an appropriate voltage reference and input RC filter. Some ADCs have additional device settings, such as Hi-Z mode or integrated digital filtering, that can be changed using the Configure Settings gear icon.
ADC stage schematic generated by Signal Chain Designer
Often, the performance of a data acquisition system is optimized by oversampling and applying digital filtering to the sampled data. By dropping a filter block after the ADC, the designer can implement a digital filter, such as a moving-average (CIC decimation) low-pass filter.
A simulator is only as good as its models. The Signal Chain Designer uses custom models for hundreds of ADI amplifiers, ADCs, and voltage references that are benchmarked against datasheet tables and plots. In any Stage View, components can be changed to optimize the circuit with the performance of a particular part. Choose to select a new component and the tool displays a Product Selection Table that is filtered for appropriate parts and can be further filtered for specific parameters.
ADC Selection Table
The Signal Chain Designer has several simulation views including frequency response, noise analysis, DC error budget, power, and input range that will be discussed later in this blog series. For other simulations, the tool exports auto-generated testbenches from the Next Steps tab that can be edited in LTspice. These ready-to-run test benches are also a very convenient way to generate LTspice schematics, complete with sources for power supplies and input stimulus, even if the full functionality of the Signal Chain Designer is not used.
LTspice testbench schematic generated by Signal Chain Designer
To learn more, see the Signal Chain Designer video series. Or try the tool directly at www.analog.com/signalchaindesigner.
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