The brains behind the Snapdragon 835

Every last square millimetre of space inside a smartphone is crammed with the electronics that make it work. Yet, the core components – the processor, the memory, the graphics chip, the cellular modem – are squeezed onto a single chip that’s no larger than a regular postage stamp.

It’s a formidable feat of engineering, the culmination of many years of work and planning. How does it all come together? We’ve been given rare access to the engineering team behind the Qualcomm® Snapdragon™ 835 Mobile Platform – the most powerful smartphone system-on-a-chip (SoC) on the market – to find out.

Years of planning

With companies such as Samsung releasing major new smartphones every few months, you might think that the components inside would move rapidly from the drawing board to production. In fact, an SoC such as the Snapdragon 835 is planned many years in advance – well before even the handset manufacturers have the first clue of what their smartphones will look like.

“What normally happens… is that you have subsystems of the chip like the modem, the graphics, the video, the memory etc. and you start that many years in advance,” Keith Kressin, Senior Vice President of Product Management at Qualcomm told us. “As you approach what the market needs, you either use or slightly modify those different cores and integrate them together to produce a chip.”

“You can’t do anything in less than a year,” Kressin added. “Even if you have the subsystems already developed, to put them all together and integrate it and do the software, it takes more than a year. So, it’s multiple years out that you start to plan these chips.”

The list of companies that Qualcomm must consult and work with to produce even one of those tiny systems-on-a-chip is daunting. There is, of course, the smartphone manufacturers, who typically start to think about what they’re going to include in their handsets 18 months in advance, and the mobile networks. Then there’s the fabrication partners that actually manufacture the chips, the battery makers, the companies that make the screens and all the other parts inside a handset. And not forgetting the huge list of international regulators who decide which chunks of radio spectrum the phone’s modem can use or how much heat the device is allowed to emit.

“That’s a huge effort in itself,” said Kressin. “If we didn’t have that, it would be very difficult to ship handsets worldwide.”

Internal debates

Then there’s teams within Qualcomm, who have to work closely and in competition with one another. Each of those different parts of the SoC has a dedicated engineering team, and they’re all vying to make their part the best it can possibly be. But when you’ve only got a limited amount of battery power to work with and strict limits on the size of the chip itself, someone has to decide which part of the SoC is going to be given priority.

“Every technology product manager wants everything to be the best – the best graphics, the best video, the lowest latency, the best power, whatever,” said Kressin. “But you need to make practical trade-offs. That’s the job of the planning lead and the project manager, to work with our principal engineers to make those trade-offs during the development of the chip.”

Not that there’s much in the way of compromise with the Snapdragon 835. The CPU has eight cores, double the number of the previous generation; it can play back 4K video at a flawless 60fps; its Quick Charge 4 technology can restore five hours of battery life in five minutes of charging; and the 4G modem is now capable of downloading data at 1Gbit/sec – the kind of speed even pure fibre broadband connections struggle to match. And it does all this in a package that’s smaller than the previous generation, despite handsets continuing to grow larger.

Keeping a lid on power

Could Qualcomm not afford to make larger, more powerful chips given that handset sizes continue to grow? No. Firstly because handset manufacturers want to fill the extra space themselves, and secondly because bigger chips drain the battery more quickly, and battery life is the “number one priority” for consumers, according to Kressin.

Yet, consumers also demand features such as voice assistants that require microphones to be running all the time or the ability to use their smartphone inside virtual reality headsets. How does Qualcomm balance the conflicting demands for more power and better battery life? “You need very fine-grained thermal management,” said Kressin, explaining that Qualcomm sets strict power limits for each of the SoC’s individual components and for the chip as a whole.

“The way you thermally stress the chip is you’re transferring files over 4G, and you have Wi-Fi running and Bluetooth running, and you’re playing a game online, and you’re stressing the CPU and GPU, and there’s machine learning in the background,” said Kressin.

“If all the systems are dynamically maxed out, then there are throttling mechanisms to make sure the chip doesn’t overheat. Most mobile devices aren’t active cooling. So, there’s very stringent power parameters on how much heat the chip can generate and how much heat can move to the surface of a device that’s often near your skin. We need to make sure we stay within that envelope all the time.”

Looking to the future

Meanwhile, of course, work is already underway on the SoCs that will be in smartphones in 2020 and beyond. The 835 is based on a 10-nanometre process – a nanometre being one billionth of a metre – and the roadmap shows that by 2020, the process will be down to 5-nanometre. That means we can expect even faster processors that generate less heat and consume less power.

“As a chip guy, we sit here and we’re planning three to five years out,” said Kressin. “In that timeframe, we can continue to get power advantages and physical size advantages through the individual process shrinking. Beyond five years, it’s much harder to see.”

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