In the past, designing a data collection system meant finding suitable combinations of components from a stack of data tables and troubleshooting the assembled prototype. Now, designers can use digital design tools to drag and drop models of sensors, analog signal conditioning blocks, analog-to-digital converters (ADCs), and digital filters into virtual signal chains, saving time and reducing detours. This software can simulate virtual chain output, allowing designers to understand how selected components affect the results, such as signal-to-noise ratio (SNR), gain and offset errors, and power.
Analog Devices, Inc.'s (ADI) digital design suite Precision Studio, including Signal Chain Designer, is not translated. This module can help designers simulate data acquisition systems before creating them. In Signal Chain Designer, users can select a sensor, set parameters for the model, and then place it into the circuit block representing the signal chain components (Figure 1).
Signal Chain Designer in ADI Precision Studio
Figure 1: Using the Signal Chain Designer in ADI Precision Studio, designers can select sensors and drag the corresponding circuit blocks into the signal chain for data acquisition component simulation. (Image source: Analog Devices, Inc.)
Before converting sensor signals into reliable data, they need to undergo multi-level processing, with each level consisting of one or more electronic components or integrated circuit IC modules, which serve as the pre-processing signal for the next level. The most common processing stage can amplify analog signals, filter analog signals, convert analog signals to digital signals, and filter digital signals.
Analog signal amplification stage
The analog signals generated by sensors often do not match the optimal input of the data acquisition system. The analog signal amplification stage uses operational amplifiers (op amps), fully differential amplifiers, voltage references, as well as passive components such as resistors, capacitors, and inductors to convert sensor signals into the effective form required by the data acquisition system.
In Signal Chain Designer, users can set the input and output types, required gain, and level shift required to achieve correct voltage input for analog amplification stages. Then, the software uses ADI products to build circuits that meet the set parameters and outputs schematic diagrams.
For example, for the sensor with 1 k Ω impedance, 1 kHz frequency, and 100 pF capacitance used in Figure 1, the user can set the gain to 2 V/V and the level offset to 2.5 V (Figure 2).
Users can set parameters such as configuration, gain, and level shift
Figure 2: User settings for analog signal amplification stage configuration, gain, level shift, and other parameters in Signal Chain Designer. (Image source: Analog Devices, Inc.)
Based on these parameters, the software constructed a circuit schematic of the analog signal amplification stage (Figure 3, top), which includes an ADA4097-2 operational amplifier. The ADA4097-2 series operational amplifier requires only 32.5 µ A current per channel to achieve a gain bandwidth product (GBP) of 130 kHz, and the peak to peak (P-P) noise between 0.1 Hz and 10 Hz is 1000 nV, with a typical 1/f noise angular frequency of 6 Hz.
The software also developed a reference circuit for the amplifier stage, which includes an LTC6655B-2.5 precision bandgap voltage reference and an AD8510 operational amplifier (Figure 3, bottom), both of which are from ADI.