Thursday, December 13, 2012

Apple iPad 4 – A6X Tear-down

Chipwork's teardown of the new Apple iPad 4 reveals a major redesign of the graphic processor (GPU). The much larger area dedicated to the GPU and wider interface of the DRAM improves the display and touch screen performance of the iPad 4. It probably also helps prolong battery life.

" The A6 is 94mm2 while the A6X is 123mm2 – a full 30% larger.So where did that extra area go? Well, firstly, it did not go to the CPU core. The A6X uses the identical CPU to the A6. Same size, same layout. This is not surprising given that the prior CPU used custom layout techniques, and therefore it would be a huge amount of work to redesign so soon. Much of the extra area has gone to the GPU cores which are up from 3 to 4. More notable is that each of these GPU cores is much larger.On the A6X each GPU core is 8.7mm2 while the A6 GPU cores are only 5.4mm2. The overall area occupied by the A6X GPU cores is more than double that of the A6!

So we see that of the 29 mm2 of new area on the A6X, a full 18.6 mm2 is the result of the increased quantity of graphics processing. Impressive!

Additionally, if you look closely at the GPU cores (which our high magnification scopes allow us to do), we can see they are actually split into sub-cores themselves. Each GPU core is sub-divided into 9 sub-cores (2 sets of 4 identical sub-cores plus a central core). This could be done to allow for more efficient parallel processing, or to allow for a higher maximum clock rate. In either case, these GPUs should result in some blazing graphics on your iPad.

Other items of note:

It looks like the A6X has double the SDRAM interface width of the A6 (again likely to allow for greater graphics processing power).

Other than the CPU, it appears all the other digital cores have new layouts. This chip is not just a minor tweak from the A6, a lot of work has gone into this.

Apple has reduced the number of core PLLs needed from 9 on the A6 to 8 on the A6X. However they have moved them close to the middle of the chip which may allow for better control over clock skew across the chip.

Many of the analog and interface cores have been reused from the A6, however there are also some new interface blocks."

Additional information

Ron Maltiel

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