What will it take to make a Retina iPad mini realistic?

In the last couple of days, it’s clear that a new Apple TV model is going to be released, but that it won’t be an explicit upgrade like the last release (which introduced 1080p output). Instead, it’s just a small component shift, and reports are saying that the real purpose of the changes to make this new Apple TV model a testbed for a new Apple chip. Why does this chip need testing? Because it might just be the one that makes a Retina iPad mini possible, which got us thinking about whether what’s rumoured is actually possible.

Basically, it looks like this Apple TV will be test run for a 32nm A5X chip, just like the last Apple TV was a trial for a 32nm A5 chip (which has since found its way into newer iPad 2s, the iPad mini and the iPod touch fifth-gen). What does 32nm mean? It refers to the size that the chips are manufactured at – you make an essentially identical chip, but you make it smaller. The original A5X was made at 45nm, meaning that it was physically larger. Reducing the manufacturing size doesn’t just have the advantage of making processors smaller, though – a 32nm processor requires less power and produces less heat than an identical one made at 45nm.

The 45nm A5X was a big power hog, but was necessary to drive the high-resolution Retina display – you need a lot of graphics power for that many pixels. This just isn’t feasible in the iPad mini, because its battery capacity is less than half that of the iPad 3. So you’ll need to change how you’re using your power, and a good first step is going from a 45nm processor to a 32nm one.

Anandtech did some extensive testing of the iPad 2 as it was originally released (with a 45nm A5 chip), the revised iPad 2 (with a 32nm A5 chip) and the iPad 3 (with a 45nm A5X chip). This gives us some great baselines to work from, because the changes are very close to what we’d expect to see in the iPad mini – the devices are just bigger.

We should say that these are very rough calculations – we can’t be more precise without more information – but they should be close enough to give us the right idea.

Switching to a 32nm A5 in the iPad 2 increased battery life by around 20% overall. It was less than 20% in some tasks and more in others, but it can be averaged to around that. We know that the iPad 3 had a battery capacity of 11,666mAh when released. So we can estimate that it would have needed 20% less battery capacity to maintain its battery life – reducing the necessary capacity to a theoretical 9,332mAh.

The battery in the iPad 3 was 70% larger than the battery in the iPad, because it required nearly double the power. The iPad mini currently has a battery capacity of 4,490mAh. If you increase that by 70% (so that it matches the comparable increase from the iPad 2 to 3, because we’re talking about using all the same components), it becomes 7,633mAh. That figure is based on the iPad 3 using a 45nm A5X though, so now we reduce that figure by 20% (for the reasons given above). Eventually, we see that the iPad mini would need a battery capacity of 6,106mAh in a Retina version to maintain its current battery life – a battery capacity increase of 36% over what it is currently.

That’s a lot. Yes, Apple managed to increase the battery capacity in the iPad 3 by 70% over the iPad 2, but it had to make it slightly larger and heavier. Apple made better use of the space inside the iPad to make the impact on size and weight even as low as it was. But it’s fair to say that Apple is already making damn good use of the space in the iPad mini.

The best bet for finding some extra space in the mini’s case seems to be whether Apple can include Sharp’s new IGZO screen technology, which not only allows for thinner screens at Retina resolutions, but also more battery-friendly ones. There’s also a potentially helpful unknown in that graphics usage was one area where switching to 32nm offered much greater gains than average – 29%. Seeing as the biggest difference between the A5 and the A5X is the GPU to drive the high-res screen, the chip could be even more power-friendly than we’ve estimated.

But there’s another problem, and it’s a much bigger one. The 20% figure we’re using is the percentage improvement in battery life overall in the iPad 2 – meaning that it includes the A5 chip, but also the likes of the storage, the wireless antenna and, crucially, the screen. We know that the screen in the iPad 3/4 draws a lot more power – the unit as a whole uses nearly double the Wattage of the iPad 2, and we know that this isn’t all down to the A5X chip. This means that the positive effects of a processor shrink will be proportionally less in an iPad 3 than in an iPad 2 – that is to say, battery life improvements would be less than 20%.

Basically, that 36% figure we’ve worked out above is probably the minimum increase necessary for an iPad mini to maintain its current battery life. No easy task.

What does this mean for an iPad mini in 2012? A 32nm A5X chip won’t be a magic bullet – it looks like other technological advances will be needed to get it right. Whether that’s denser battery technology, an IGZO screen or better use of internal space, Apple will only do it when it’s ready, which might not be for a while.