Effect of the temperature on BMI270 readings

[Myzhar]

Hi,
testing the effect of the temperature on BMI270 readings I noticed a strange behavior. I expected to see a drift on readings according to increasing temperature, instead I see many different steps, like if there is something acting internally to compensate the changing temperature.
I searched on the datasheet, but I have not found any explanation.

You can appreciate what I'm saying in the attached 30' plot of the Gyro value for the Z axis where also the temperature value is reported.

Any idea about what can be the cause of those steps?

PS the sensor was steady and I verified that nothing was acting on it while testing.

[o_o · Accepted solution]

Hi Walter,

I can confirm that this expected behavior, but also that these "steps" are much smaller than the noise floor. It is indeed an artifact of the temperature compensation and cannot be disabled.

The offset stability of BMI160 is also not perfect. In case your application is more sensitive to offset stability, then BMI085 is an order of magnitude more stable.

"The behavior of BMI160 is predictable and the effect on temperature on readings can be compensated by software."
I also want to point out that all parts are calibrated at the factory, and that further TCO calibration will vary part to part (not necessarily in the same direction), and also be impacted by the soldering process, and mechanical stress (for example by using 4 mounting screws instead of 3).

o_o

[sebmadgwick]

o_o, you've said that the "BMI085 is an order of magnitude more stable".  I do not see this in the datasheets.  Are you mistaken?

Gyroscope characteristic	BMI270	BMI085
Sensitivity temperature drift	0.02 %/K	0.03 %/K
Zero-rate offset change over temperature	0.015 dps/K	0.015 dps/K

Sources:

• https://www.bosch-sensortec.com/media/sensortec_1/downloads_2/documents/product_related_documents/da...
• https://www.bosch-sensortec.com/media/sensortec_1/downloads_2/documents/product_related_documents/da...

[o_o]

Hi sebmadgwick,

Thanks for correcting me, I was thinking about BMI160 and not BMI270. However, there is a fundamental architecture difference between the BMI160/BMI270 and the BMI055/BMI085/BMI088.

The BMI085 is using what we call a "closed-loop" gyroscope architecture which is common in automotive IMUs, but unique in the consumer electronics space. There is an additional control loop that actively moves the MEMS structure using electrodes to eliminate the errors induced by temperature. This does have one major downside in the higher current consumption and voltage requirements.

BMI160/BMI270 are what we call "open-loop" gyroscopes, where the error is measured and compensated with digital filters, instead of physically moving the MEMS structure back into place. This approach is much lower power, but has some downsides such as short term drift and overall worse non-linearity.

From the specifications alone, these effects are difficult to quantify, but the BMI085 is the combination of our BMG160 closed-loop gyroscope, which is our most stable gyroscope in temperature, and our BMA456, which is our most stable accelerometer in temperature.

Hope that clarifies my previous comment.

o_o