editor's blog
Subscribe Now

Small single-package IMU

Bosch-Sensortec recently announced a new integrated IMU, the BMI055.

Which, amongst other things, brings up the question: exactly what is an IMU? While researching this for a gyroscope article couple of years ago, I found that the term (which stands for “inertial measurement unit”) was used to refer generically to a class of sensors that use some type of inertia as a way of sensing motion. That inertia might be linear (using an accelerometer) or rotational (using a gyroscope).

The definition Bosch-Sensortec used differed from that, and as I look around now, I see other usage that is similar: an IMU is a combination of sensors – in particular, accelerometers and gyroscopes – for detecting motion. (Some so-called IMUs also include other sensors like magnetometers and possibly even a pressure sensor/barometer, for a so-called 10 degrees of freedom – 6 of which degenerate to 3). Whether this represents a change or simply varying definitions is unclear to me (it’s hard to recreate the internet of a couple years ago). Nonetheless, the term is, to some extent, overloaded; the combo definition seems to predominate now.

While we’re on definitions, you might think of a magnetometer, when used in a navigation application, as a compass (or eCompass) by analogy to an old-school needle compass, which is simply a magnetometer. But that’s not how the MEMS version is defined: a MEMS compass is the combination of an accelerometer and a magnetometer.

To be clear, Bosch-Sensortec announced what they claim to be the smallest combination accelerometer/gyroscope available. It is a multi-die integration (both with respect to the MEMS sensors and the accompanying ASICs); the size advantage comes from housing them in the same package.

As to whether those dice might ever merge, they said that it might happen, but that it’s more likely that the ASICs and MEMS chips will independently merge first, possibly followed by full MEMS/CMOS integration.

They’ve added a power-saving feature through this integration: the accelerometer can wake up the gyroscope. Gyros are notoriously power-hungry; you have to keep the proof mass moving (unlike an accelerometer). So the BMI055 allows the gyro to be turned off. Which isn’t a first, but they’ve sped up the wake-up time from a more typical 30 ms to 10 ms. This is intended to allow the gyro to be woken by the accelerometer without it taking so long that the gyro misses an event. The effect is to cut power in half.

The combined unit comes with free fusion software. There have been two ways of approaching fusion software: using either “tight” or “loose” coupling. Loose coupling means that the data from each sensor is independently processed to some degree before being presented for munging with the output of other sensors. Tight coupling performs the fusion with the raw data from the sensors.

Loose coupling is easier to do (and less reliant on the low-level data format of a sensor), but it’s less accurate. Tight coupling provides a more accurate result, but is more complex and needs to work at the lowest data level (which ties it more closely to the specific sensor).

Bosch-Sensortec uses both: where loose coupling provides sufficient accuracy, they use it, reverting to tight coupling when necessary. Where they make that cut is something they’re keeping to themselves.

You can find more information in their release

Leave a Reply

featured blogs
Aug 13, 2020
My first computer put out a crazy 33 MHz of processing power from the 486 CPU. That was on “Turbo Mode” of course, and when it was turned off we were left with 16 MHz. Insert frowny face. Maybe you are too young to remember a turbo button, but if you aren’t ...
Aug 13, 2020
Hi readers! Welcome to Veri-Fire, a blog series that helps you deep dive into Virtuoso® ADE Verifier and learn about its various whys and hows. In this series, Walter Hartong, a Product... [[ Click on the title to access the full blog on the Cadence Community site. ]]...
Aug 13, 2020
Imagine ambling into a small town, heading to the nearest public house to blow the froth off a few cold beers, and hearing your AI whisper '€œ...'€...
Aug 7, 2020
[From the last episode: We looked at activation and what they'€™re for.] We'€™ve talked about the structure of machine-learning (ML) models and much of the hardware and math needed to do ML work. But there are some practical considerations that mean we may not directly us...

Featured Video

Product Update: New DesignWare USB4 IP Solution

Sponsored by Synopsys

Are you ready for USB4? Join Gervais Fong and Eric Huang to learn more about this new 40Gbps standard and Synopsys DesignWare IP that helps bring your USB4-enabled SoC to market faster.

Click here for more information about DesignWare USB4 IP

Featured Paper

Improving Performance in High-Voltage Systems With Zero-Drift Hall-Effect Current Sensing

Sponsored by Texas Instruments

Learn how major industry trends are driving demands for isolated current sensing, and how new zero-drift Hall-effect current sensors can improve isolation and measurement drift while simplifying the design process.

Click here for more information

Featured Chalk Talk

uPOL Technology

Sponsored by Mouser Electronics and TDK

Power modules are a superior solution for many system designs. Their small form factor, high efficiency, ease of design-in, and solid reliability make them a great solution in a wide range of applications. In this episode of Chalk Talk, Amelia Dalton chats with Tony Ochoa of TDK about the new uPOL family of power modules and how they can deliver the power in your next design.

Click here for more information about TDK FS1406 µPOL™ DC-DC Power Modules