Apple gives a foundry lesson

October 23, 2015 //By Kevin Krewell
Apple gives a foundry lesson
The rush to analyze Apple products has led to distorted conclusions from some who fail to appreciate the nuances of semiconductor technology, says one analyst.

People in the market for an iPhone 6s or 6s Plus, may have heard that there’s two different chips (Apple’s A9 SoC) powering the phones – one manufactured by Samsung and the other by TSMC. While the chip from both foundries are supposed to perform identically, the manufacturing processes used by TSMC and Samsung are not the same.

Once the secret of the Apple dual sourcing was out, gadget Web sites began testing the phones to compare the two version of the A9 processor. The result showed that the two versions do not appear to operate exactly the same. This could have a legitimate impact on which phone consumers chose, depending on how they use their phones. This situation has led to some consumer concerns that may have been inflated by some unrealistic testing.

One real difference is the physical size of the SoC - the Samsung die is 8% smaller than the TSMC chip. The size difference could be due to some small difference in the transistor size. Both companies have new 3D transistor processes - TSMC advertise its process as 16 nm FinFET, while Samsung calls its process 14 nm FinFET, implying the Samsung transistor should be smaller than the TSMC transistor. But the process names are no longer directly connected to process feature sizes and are now more marketing designations.

The difference in die size might also be explained by the different design libraries used to build the two chips. Even though the chips are functionally identical, the A9 design team had to work with each foundry’s unique design libraries. For example, the SRAM cell used for caches can differ in transistor count and area depending on the design of the standard library. But this difference in die size should not impact a consumer's experience in any way.

Testing from a number of sites have shown that there’s another difference – the TSMC parts (at least those few tested so far) have shown to have longer battery lives than the Samsung version. The actual extent of the difference is a matter of some controversy. Some tests, like GeekBench and AnTuTu, have shown a significant difference in battery life between the two chips.

Apple felt compelled to comment. The company said the differences should be only 2 to 3% in real world conditions. Apple’s response gets to the core of the problem: Were the tests real world enough? The tests did show that under heavy CPU-focused processing, the battery did drain faster. But in real world conditions, a normal user would use the CPU periodically, not constantly. That said there does seem to be some significant differences between the two chips and the question is why the difference.

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