The smartphone represents one of the biggest changes in our world. In less than thirteen years, we’ve gone from a few people owning a dumb phone to the majority of the planet owning a smartphone (~83.7% in 2022, according to Statista). There are very few things that a greater percentage of people on this planet have. No drinking water, no housing, not even food.
How does a smartphone work? Most people have no idea; they are incredibly complicated devices. However, you can break them down into eight sub-modules, each of which is simply complex. What makes them work is that each of these components can be small, with huge economies of scale, and are tightly integrated, allowing for easy assembly.
So, without further ado, the eight fundamental elements of the modern cell phone are: the application processor, the baseband processor, a SIM card, the RF processor, sensors, a display, cameras and lenses, and power management. Let’s take a look at them all, and how they fit together.
When you think computer or, by extension, smartphone, you think of a single cohesive unit that powers what your smartphone does. However, even setting aside universal multi-core processors, the processing inside your phone isn’t a single voice, but a cacophony of arguing voices. The Application Processor (AP) is what we think of as this traditional brain. It has a large multi-core processor, almost always ARM-based.
These access points can be part of an extended system-on-chip (SoC). The SoC can include memory, GPU, digital signal processors, image processing units, modem (which we will come to later), and other minor items like video decoders and AI engines .
But back to the CPU. It runs your phone’s operating system and is primarily the ringleader in your phone’s decisions. Nowadays it often has big powerful cores which consume much more power and small cores which consume much less power. This is usually done by having the smaller cores dispatched all at once, in order, while the larger cores are massive multiscalar cores out of order. We could spend enough time breaking down the different parts of a modern CPU, but we think you could learn better. by making your own or repair a broken simulation.
The baseband processor (BP) is an entirely separate processor to which the access point can communicate, often referred to as a modem. Even the iPhone, which has its own custom hotspot, uses a Qualcomm or Intel BP. Typically, Wi-Fi, Bluetooth, and other radio-type communications are handled by the AP, and the BP focuses entirely on cellular communications. Even the old 3G protocol specifications are long and dense, with each revision adding complexity. Complex power amplifiers, multiband-multimode transceivers and other techniques add up to a complex circuit.
Baseband processors have their own firmware and RAM, and codebases are manufacturer-specific opaque binaries. There is a good conversation about hack an old usb 3g modem. In fact, some of the Intel modems in some iPhones models had x86 processors. [Comsecuris] detailed a buffer overflow they found in many iPhone modems which gives useful information on the inner workings.
We think of them as just storage, but the small piece of carrier-branded plastic with the gold contacts handle contains a small chip. Everything is as per specifications, but the interactions between the AP, BP and SIM cards have become quite complex. SIM cards step into the security spotlight, as they are updated remotely with little user control. They can talk to the BP without the AP knowing. Can you imagine your phone calling or texting someone, and the only way to find out would be to check your phone records? Your phone already does. We’re slowly moving away from SIM and towards eSIM, but that’s a long way for most of us.
Sensors make your phone much more aware of its surroundings. Cameras, GPS, microphones, distance sensors, proximity sensors, gyroscopes, accelerometers, altimeters, magnetometers, LIDARfingerprint sensors, radar sensors, ambient light level sensors, and pressure sensors are all common additions to adorn our smartphones.
The amount of streaming data can be truly staggering. Many of these sensors have their own microprocessor to manage the load and present a more consistent view to the AP. In reality, some phones have coprocessors to manage these different sensors in a more energy efficient way. So we have the AP talking to a coprocessor, talking to microprocessors, and reading sensors. All of these sensors go a long way towards making a smartphone much more useful on a day-to-day basis. You can call, get directions, rotate for portrait mode or use your phone for physics experiments.
Smartphone screens are a marvel. They have a resolution that matches or beats many home TVs while being high quality and affordable. Used phone screens are often used in projects here on Hackaday because they are easy to find and drive. We see progress here with OLED screens and microLED screens. As the screen is often the front of your phone, having it to heal himself would be very convenient. Smartphone screens are nothing special because they are just miniaturized versions of larger panels.
Modern cameras on smartphones are crazy.
For example, the lenses of modern smartphones are crazy. Here is the design used on the iPhone 7; each lens element is highly aspherical with a very large number of correction coefficients; this goal completely breaks the existing poly optic implementation of the 2016 article. pic.twitter.com/cYr9qsa5Bj
— Yining Karl Li (@yiningkarlli) February 27, 2022
Lenses and sensors are unique in many ways. Unlike screens, where you can scale down the process, light and lenses get weird when they’re small. So how do you catch more light in a smaller area? A incredible (although long) the lens design resource is here which details how we proceed. Lens design is a complex art with a long history of iteration and improvement since the early 1800s. There are several notable inventions listed in the link above. We could do a whole article on camera lenses. In particular, the long exposures of old cameras had as much to do with lens design as with film.
The lens and sensor go crazy, but the image signal processor (ISP) that processes the photos going mad too, in some cases blatantly lying. Like a traditional signal processor, the ISP takes an image and processes it, applying some transformation. However, while some filters are done on the AP – think Snapchat filters – the actual sensor reading and image formation is done by the ISP.
The phones are mobile and should last a long time on battery power. Like other battery-powered products, there is a Battery Management System (BMS) that takes care of the battery. However, there are quite high demands placed on it. It needs to charge wirelessly and at incredibly high rates and often. On the other hand, efficiency is factored into all the other parts we discussed. There are power modes on each module. Each component is reviewed against the budget, both monetarily and against the energy budget.
In our modern society, we frequently replace our smartphones, and our world seems to have no end to our hunger for them. So, with more and more smartphones being scrapped every year, packed with features and processors, why don’t we hack them more? They make a perfect companion for your 3D printer.
There have been a few attempts to make smartphones modular, allowing you to swap out the baseband processor, display, or camera. However, the concept seems to be at a standstill. In particular, the application processor, baseband processor and sensor unit are so tightly connected in many modern phones that swapping out any of the components would be like redesigning the whole thing from scratch. Smartphones are valuable because of their scale and tight integration, and it’s simply hard to beat.
However, it is amazing all the way in smartphones in general. At Hackaday, we can’t wait to see what the next decade has in store for us.