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Tackling IoT and Industry 4.0 sensor backplane needs

Posted: 28 Apr 2016 ?? ?Print Version ?Bookmark and Share

Keywords:Internet of Things? IoT? Industry 4.0? network sensors? PHY layer?

The Internet of Things (IoT) sensor backplane is fuelling a need to associate multiple sensor inputs into a single node in order to minimise the workload on the wireless gateway and enable unobtrusive and cost effective form factor solutions. These are also needs as defined by Industry 4.0 requirements where intelligent network sensors are called upon to provide fully automated control environments in an industrial factory setting, accounting for multiple sensed parameters. These parameters include temperature, pressure, flow, position and more. The sensor backplane is also called upon to support the PHY layer interface to wired communication protocols minimising the number of system components.

This bimodality requires that the node interface manage various input and output signals and as a result manage different signal conditioning solutions. In this paper we discuss the benefits of a configurable analogue architecture integrated into a 16bit microcontroller (MCU) which provides for the signal conditioning requirements of various sensor nodes. The modular analogue architecture is configurable via register settings and enables dynamic interfacing across different analogue modules and through the microcontroller for additional data processing. Provided are several signal conditioning circuit examples enabled by the configurable sensor interface as required in many IoT and Industry 4.0 sensor backplanes and comparison of actual circuit results with corresponding SPICE simulations of the signal conversion.

Benefits of embedded flexible analogue architectures
The analogue front-end provides a bridge between the real world signal and the microcontroller for end node solutions that make up the IoT and Industry 4.0 sensor backplanes. The signal conditioning implementation converts the continuous time domain signal into a digital bit stream that can be processed by the embedded MCU to either provide real-time calibration of the sensor output parameters and subsequent signal conditioning or to act on the world around it C in this case, in the form of digital-to-analogue converters (DAC).

The digitally controlled analogue modules of the configurable analogue architecture perform a critical signal transformation to ensure signal compatibility within the system. The analogue sensor front-end may be called upon to amplify the signal so that it may fit the range within the data converter specifications for analogue-to-digital conversion (ADC). It may also provide a conversion of a sensor output current signal to a corresponding voltage signal so that it can be further converted into the digital domain. Additionally, the signal conditioning circuit must manage amplification of differential voltage signals commonly used in most resistive bridge circuits. Finally, the output response of the sensor may introduce high frequency or low frequency noise which interferes with the primary signal response. The signal conditioning circuit provides for the appropriate filtering solution whether as a low pass or high pass filter.

Having the sensor signal conditioning integrated into the microcontroller provides for better system power consumption as functionality is distributed in a single chip. This also translates to increased throughput with faster system switching times and a reduction in system noise. Inherently these mixed signal designs will also lead to simplified system designs with pre-verified aspects of the component integration. Signal and power integrity conformance to device specifications is verified through specification-based functional validation. This allows the system designer to speed up the design process as functional verification of the flexible analogue architecture and MCU blocks is carried out across different modes of operation. This alleviates concerns to susceptibility to noise associated with power supply, cross talk and random noise (burst, flicker, shot, thermal etc.). Design layout is additionally optimised to assure proper signal and power integrity without excessive isolation, which can significantly increase die size. Overall the single-chip solution which handles the signal conditioning of multiple sensor inputs results in a reduction of the bill of materials (BOM) and PCB board size. A number of end-equipment applications within the IoT and Industry 4.0 space can benefit from the small form factor and low power solutions enabled by the embedded configurable analogue architecture.

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