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
Nov 23, 2022
The current challenge in custom/mixed-signal design is to have a fast and silicon-accurate methodology. In this blog series, we are exploring the Custom IC Design Flow and Methodology stages. This methodology directly addresses the primary challenge of predictability in creat...
Nov 22, 2022
Learn how analog and mixed-signal (AMS) verification technology, which we developed as part of DARPA's POSH and ERI programs, emulates analog designs. The post What's Driving the World's First Analog and Mixed-Signal Emulation Technology? appeared first on From Silicon To So...
Nov 21, 2022
By Hossam Sarhan With the growing complexity of system-on-chip designs and technology scaling, multiple power domains are needed to optimize… ...
Nov 18, 2022
This bodacious beauty is better equipped than my car, with 360-degree collision avoidance sensors, party lights, and a backup camera, to name but a few....

featured video

Unique AMS Emulation Technology

Sponsored by Synopsys

Learn about Synopsys' collaboration with DARPA and other partners to develop a one-of-a-kind, high-performance AMS silicon verification capability. Please watch the video interview or read it online.

Read the interview online:

featured paper

How SHP in plastic packaging addresses 3 key space application design challenges

Sponsored by Texas Instruments

TI’s SHP space-qualification level provides higher thermal efficiency, a smaller footprint and increased bandwidth compared to traditional ceramic packaging. The common package and pinout between the industrial- and space-grade versions enable you to get the newest technologies into your space hardware designs as soon as the commercial-grade device is sampling, because all prototyping work on the commercial product translates directly to a drop-in space-qualified SHP product.

Click to read more

Featured Chalk Talk

Direct Drive: Getting More Juice from Your JFET

Sponsored by Mouser Electronics and UnitedSiC

In this episode of Chalk Talk, Jonathan Dodge from UnitedSiC (now part of Qorvo) and Amelia Dalton discuss how you can take full advantage of silicon carbide JFET transistors. They delve into the details of these innovative transistors including what their capacitances look like, how you can control their speed and how you can combine the benefits of a cascode and a directly driven JFET in your next design.

Click here for more information about UnitedSiC UF4C/SC 1200V Gen 4 SiC FETs