editor's blog
Subscribe Now

Old-School Analog Outputs

Today we looked at the role of Freescale’s new FXLN83xxQ accelerometer for analyzing vibrations. But one feature of the accelerometer had me cocking an eyebrow: analog outputs.

We’ve covered a lot about sensors here before, and in the huge majority of the cases, a sensor consists of a MEMS (or other) sensing element, an ASIC to clean up and digitize the signal, and then a series of registers where all the relevant data gets placed.

An outside entity, like a sensor hub, can then read those registers over a bus connection – typically I2C or SPI. What could be simpler?

Well, I guess an analog output could be simpler: you eliminate all of that messy digital stuff. But it seems to me that, running an analog signal halfway across town to get it to the analog inputs of a microcontroller (aka MCU, or whatever hub is used) would run the risk of seriously degrading the analog value in a way that wouldn’t happen with a digital signal.

XL_schematic_red.jpg

 

(Click to enlarge)

Image courtesy Freescale.

I asked Freescale about this, and they justify it based on the wide variety of digital interfaces in use, in particular in industrial settings. Heck, they say that even CAN bus is leaving the confines of vehicles and moving into other applications.

Freescale makes lots of microcontrollers. This variety of MCUs partly reflects the diversity of interfaces they may talk to: Rather than having one large unit with all possible interfaces, they offer different devices. And yes, they’re assuming (or at least hoping) that you’ll be using their MCU.

So the idea goes thusly: first off, you simply don’t run the analog signals halfway across town. In these applications, an MCU is likely to be right nearby. (If not, then you want to move it so that it is nearby.) The MCU you choose will then reflect whatever bus you’re using, and that’s where you go digital. They prefer this, obviously, to having to have a bunch of different versions of the sensor to suit the various digital protocols.

There’s one other convenient thing about digital registers, however: they’re good at storing values while the rest of the system goes to sleep for a while to reduce power. Well, apparently these analog outputs can manage the same trick. The internal electronics shut down between samples, but the output is held between samples. This decouples the rate at which the MCU samples the analog outputs from the rate at which the sensor samples the system and allows power as low as 200 µA when running.

That’s how they see it; if you see it differently, then your comments are encouraged below.

Leave a Reply

featured blogs
Sep 22, 2021
3753 Cruithne is a Q-type, Aten asteroid in orbit around the Sun in 1:1 orbital resonance with the Earth, thereby making it a co-orbital object....
Sep 21, 2021
Placing component leads accurately as per the datasheet is an important task while creating a package footprint symbol. As the pin pitch goes down, the size and location of the component lead play a... [[ Click on the title to access the full blog on the Cadence Community si...
Sep 21, 2021
Learn how our high-performance FPGA prototyping tools enable RTL debug for chip validation teams, eliminating simulation/emulation during hardware debugging. The post High Debug Productivity Is the FPGA Prototyping Game Changer: Part 1 appeared first on From Silicon To Softw...
Aug 5, 2021
Megh Computing's Video Analytics Solution (VAS) portfolio implements a flexible and scalable video analytics pipeline consisting of the following elements: Video Ingestion Video Transformation Object Detection and Inference Video Analytics Visualization   Because Megh's ...

featured video

Accurate Full-System Thermal 3D Analysis

Sponsored by Cadence Design Systems

Designing electronics for the data center challenges designers to minimize and dissipate heat. Electrothermal co-simulation requires system components to be accurately modeled and analyzed. Learn about a true 3D solution that offers full system scalability with 3D analysis accuracy for the entire chip, package, board, and enclosure.

Click here for more information about Celsius Thermal Solver

featured paper

IPU-Based Cloud Infrastructure: The Fulcrum for Digital Business

Sponsored by Intel

As Cloud Service Providers consider their investment strategies and technology plans for the future, learn how IPUs can offer a path to accelerate and financially optimize cloud services.

Click to read more

featured chalk talk

Build, Deploy and Manage Your FPGA-based IoT Edge Applications

Sponsored by Mouser Electronics and Intel

Designing cloud-connected applications with FPGAs can be a daunting engineering challenge. But, new platforms promise to simplify the process and make cloud-connected IoT design easier than ever. In this episode of Chalk Talk, Amelia Dalton chats with Tak Ikushima of Intel about how a collaboration between Microsoft and Intel is pushing innovation forward with a new FPGA Cloud Connectivity Kit.

Click here for more information about Terasic Technologies FPGA Cloud Connectivity Kit