SAN JOSE, Calif. – Apple apparently tested a three-axis gyroscope from InvenSense in its iPad, but probably plans to use a similar device from STMicroelectronics in a future version of the tablet, according to an analysis by UBM TechInsights.
The Apple iPhone 4 was the company's first smartphone to uses a three-axis gyroscope, specifically the L3G4200D from STMicroelectronics. The chip is geared to provide more detailed position information than an accelerometer or GPS.
“It seemed strange at the time that a product like the iPad would have been designed to not include a gyroscope but an iPhone 4 that was being designed at around the same time would,” said Steve Bitton, a product manager at UBM TechInsights that did a teardown of the iPad. UBM TechInsights is part of United Business Media, the publisher of EE Times.
In his teardown, Bitton discovered an unpopulated 24-pad spot next to an STMicro STM33DH accelerometer on an iPad circuit board. A circuit board on the iPhone 4 uses the same accelerometer and places next to it an STMicro L3G4200D gyro, but that chip requires just 16 pads.
"That told us maybe [Apple had] another part in mind,” for the original iPad, Bitton said.
The only other three-axis digital gyroscope available on the market at that time was the ITG-3200 from InvenSense, and it required a 24-pad interface, according to TechInsights. Bitton subsequently traced the digital output from the gyro on the iPhone 4 to its A4 processor and found similarities to the signal path between the iPad processor and the empty 24-pad space on the iPad board.
As a follow up, TechInsights used a SkyScan 1173 microtomography system from Micro Photonics, Inc. to take X-ray images of the iPhone 4. “In order to perform signal tracing without removing any part from the iPhone, we used slices parallel to the plane of the PCB, and were able to change the Z-axis to step through the metal layers," Bitton said.
The conclusion, Bitton said, "is that Apple was possibly testing the idea of a gyroscope within the iPad and had done so using the ITG-3200 by InvenSense as it was the first digital three-axis gyroscope to be released," he said. "Apple probably chose to wait until the next iteration of the iPad to introduce gyroscope capabilities [and plans] to use [the] ST Micro’s L3G4200D to reduce the amount of [software] development required,” he added.
TechInsights plans to post a video online explaining its analysis. It has already released an analysis of the iPad's A4 processor.