Apple Uses Nine Degrees-of-Freedom Sensing in the iPhone 4

Posted by  21 September 2010

The iPhone 4 is the first portable consumer device to feature full nine degree-of-freedom (9-DoF) inertial sensing. Apple have done this by integrating a three-axis accelerometer and a three-axis gyroscope from STMicroelectronics (ST), together with an electronic compass from AKM.  The iPhone product line has moved steadily towards this goal with each successive model. Steve Nasiri and his Invensense colleagues discussed the benefits of 9-DoF sensing in some detail in a recent Whitepaper.


The original 2G iPhone, released in 2007, featured an ST 3 mm x 5 mm LIS302DL three-axis accelerometer. This provided the screen orientation function, by using the acceleration of gravity to determine the orientation, and it was also available to “app” developers for simple games. The iPhone 3G also only contained an accelerometer, but in this case Apple used the 3 mm x 3mm LIS331DL MEMS device, also from ST. Next up, the iPhone 3GS added digital compass capability by adding an AKM AK8973 electronic compass.  This provided improved GPS location functionality, even though (as described on an AKM web site) it required regular recalibration by waving the phone in a figure-eight motion  – no, it’s not a tai-chi app!

The iPhone 4 features an ST LIS331DLH three-axis accelerometer and an AKM AK8975 three-axis electronic compass. To get the 9-DoF, Apple added an ST L3G4200D three-axis gyroscope sensor, packaged in a 4 mm x 4 mm LGA package.
Chipworks has examined all of the inertial sensors found in the iPhone product family and detailed reverse engineering analysis reports are now available. The following is a summary of our findings for the sensors found in the iPhone 4;

Read the full teardown here.

Last modified on Tuesday, 21 September 2010 11:13