NewsBytes Explainer: Why iPhone 13 LTPO display tech is game-changing
Apple switching to new LTPO-enhanced OLED displays for the iPhone 13 is considered the next significant advancement in smartphone hardware. It's such a big deal that industry analysts predict it will become the dominant display technology in the next two years. That's significant because displays are not only our primary means of interaction with smartphones, but they also significantly affect battery life.
Problem #1: No one knows how or why LTPO's better
However, try looking for an explanation on what exactly makes Apple's LTPO-powered OLED display tech special, and you will find articles explaining how it will enable high refresh rates while lowering power consumption. But wait just a minute there, mister! Mid-range smartphones already come equipped with LCDs sporting variable refresh rate technology. So, how does Apple implementing an existing feature suddenly make it special?
Problem #2: iPad Pro already has variable refresh rate tech
And here is another kicker—the 2018 iPad Pro already has Apple's ProMotion variable refresh rate technology scaling up to 120Hz. This categorically debunks prevalent theories attributing the magical properties of the LTPO display to variable refresh rate. Let's now demystify the complicated underpinnings of Apple's LTPO display technology to understand the real reason behind its significance.
But first a primer on OLED v/s LCD technologies
Apple's LTPO display tech is significant because it offers higher refresh rates while also reducing battery consumption by approximately 15 percent. To figure that out, we must first understand why OLED displays are more power efficient than their LCD counterparts. That's primarily because OLEDs are emissive displays, where individual pixels generate light, whereas LCDs are transmissive and must rely on an external light source.
Why only OLEDs benefit from power-efficiency of Always-On Display technology?
The Always-On Display (AOD) feature demonstrates this concept quite well. For instance, an OLED display can switch 95 percent of the pixels off while rendering a digital clock against a black background. The display's battery consumption is, therefore, significantly reduced. The same isn't true for LCD panels. Here, the pixels don't emit light, but can only block/allow the same generated by the backlight.
Meanwhile, switching off an LCD pixel doesn't really save power
Even if 95 percent of LCD pixels are oriented to block the backlight, the latter remains active irrespective of the state of the pixels. The AOD feature, therefore, offers no measurable power savings for devices bearing LCD technology. In other words, although the 2018 iPad Pro has ProMotion's variable refresh rate, the very nature of its LCD panel precludes it from meaningful power savings.
What exactly does a backplane do in a display?
Now that we have the basics in order, let's understand what constitutes an LTPO display. It is a special OLED backplane technology developed by Apple and manufactured by Samsung. What is a backplane, you ask? That is the part of the OLED display responsible for switching the individual pixels on and off, while also supplying electric current in order to control their light intensity.
Traditional amorphous silicon backplanes aren't fast enough
These are technically called Thin-Film Transistor (TFT) backplanes, because they use transistors to control individual pixels in order to create coherent images. Traditional TFT backplanes use amorphous silicon (a-Si) as the active layer. However, a-Si backplanes lack high carrier mobility, or the speed at which electrons move within them. This means, they can't switch the pixels fast enough for high refresh rate (120Hz) displays.
Enter LTPS backplane technology enabling high refresh rate displays
One way to fix the low carrier mobility of a-Si backplanes is through heat-treatment using laser beams to transform the amorphous silicon into the polycrystalline variety. Such TFT backplanes with Polycrystalline Silicon (poly-Si) active layers are called Low-Temperature Polycrystalline Silicon (LTPS) backplanes. This backplane technology forms the bedrock of all high refresh rate displays available today, whether it's used in OLEDs or LCDs.
Why did Apple choose to design a new display backplane?
What would have compelled Apple to create a new backplane technology? Apple has been late to the high refresh rate display party because it wasn't happy with the higher battery consumption. Leveraging variable refresh rate is one way of reducing battery usage. The display only needs to be responsive when the user is interacting with it or when it's fed with fast-paced video/interactive content.
Prevalent LTPS backplane technology has one serious shortcoming
A display can be refreshed once a minute when displaying a clock, or never while browsing websites displaying static images and text unless it is interacted with. Furthermore, only parts of a website displaying, say, video can be refreshed. While current LTPS backplanes can reduce power consumption by switching the display at a lower frequency, they aren't very power efficient at another important aspect.
High leakage current negates low refresh rate power savings
We already went over the first display backplane component (switching circuit) controlling the refresh rate. The other one (driving circuit) delivers power to each individual pixel. At lower refresh rates, the driving circuit of the LTPS backplane becomes a problem due to its high leakage current. That represents the parasitic power draw of a transistor even when it is switched off.
LTPO backplane combines LTPS and IGZO active layers
Apple's primary requirement was reducing the leakage current of the driving circuit, in order to maximize power savings when switching off large groups of pixels. That is the underlying reason for which Apple developed the LTPO backplane. LTPO stands for low-temperature polycrystalline oxide, which is a hybrid backplane using LTPS active layer for the switching circuit and IGZO active layer for the driving circuit.
LTPO is characteristic of Apple's uncompromising approach to engineering
The driving circuit's Indium Gallium Zinc Oxide (IGZO) active layer is the secret sauce in Apple's LTPO backplane technology. The low leakage current of this driving circuit allows LTPO displays to reduce battery usage by up to 15 percent when paired with variable refresh rate technology. The IGZO driving circuit significantly reduces the parasitic power draw from inactive pixels during low refresh rate cycles.
Apple's bespoke display tech could truly be a game changer
If everything goes right, the LTPO display (rumored to debut with the iPhone 13) could potentially reduce battery consumption by up to 15 percent by making the variable refresh rate technology a lot more power efficient than it is in traditional LTPS displays. This should allow the iPhone 13 to deliver similar or even better endurance without being compelled to use a larger battery.
