Engineering specs, discussions emerge for Apple Watch Series 4 LTPO-OLED screens

Following Apple’s announcement last week, you may have notice that the Apple Watch Series 4 unit incorporates a “LTPO-OLED” screen.

Here to explain what that is, a quick engineering discussion screen cap offered the following details:

Apple’s watch comparison [Source : 0]
Section 1: What are backplanes

Before we can understand what the LTPO OLED really is, we need to understand the current state of OLED displays.

When high resolution/large size OLED displays are involved, as in the case of high resolution Televisions and the increasingly common high resolution OLED displays on iPhones, there is a need to drive the large number of pixels correctly.

This is accomplished by something called the Backplane which is a Thin Film Transistor(TFT) layer that activates the OLED pixels and control the current going to the OLED layer which then determines what they show and at what brightness. This is because unlike LCD’s, OLED’s produce their own light and so the Backplanes need to take on the dual role of LCD’s Backplane and the Backlight by providing both the control voltage and the driving voltage to the OLED matrix. As a result OLED backplanes play a pivotal role in the OLED technology.

Amoled vs Amlcd [Source : Google Images, might be subject to copyright]
On the other hand, LCD TFT backplanes let the light from the backlight go through and apply a controlling voltage to the Liquid Crystal Layer to determine what is shown on the screen. In essence, LCD’s backplanes have a lesser responsibility than their OLED counterpart as the ‘pixel-activation’ aspect is absent.

TL;DR Section 1:
It is important to note that Backplanes act as puppet masters for the displays that we see, silently synchronising millions of pixels at 60 or so times a second. On OLED they take on the additional responsibility of activating the OLED Pixels due to the absence of a backlight, whereas LCD screens, they only apply the controlling voltage to the Liquid Crystals. So any changes to this backplane technology plays a massive role in the overall performance and power utilisation of OLEDs.

Section 2: Current Backplane technologies
The major three Backplane technologies used in both LCD and AMOLED include LTPS, IGZO and a-Si which are respectively Low Temperature Polycrystalline Silicon, Indium Gallium Zinc Oxide, and Amorphous-Silicon.

IV Backplanes [Source : 1]
The graphs above show the IV curves of the three types of most commonly used backplanes. Backplanes include transistors and Capacitors to drive the OLED panels, but in the simplest terms,
The negative X-axis shows the current leakage when the transistor is off. The lower the value here the better the power savings as the standby drainage for switched off pixels is less.

The positive X-Axis shows the current supply to the OLED layer above the Layer when the pixel is switched on. The higher the value the more the current is supplied to the OLED layer and the better looking/performing is the display. LTPS backplanes are best in this regard (owing to the inherently high electron mobility) but however drain some current even when the transistor is off.
Apple currently uses LTPS Backplanes in its iPhones [Source : 3]

Section 3: So, what is LTPO?
Put simply, LTPO, Low Temperature Polycrystalline Oxide is essentially a hybrid of LTPS and IGZO giving the high current when the transistor is on and the low power drain when the transistor is off.

The rest of the piece dives pretty deep as to what’s happening on the engineering end, what new technologies are in place, and the science behind them.

Click the link below for the full story, take a gander, and please let us know what you make of your Apple Watch Series 4 once it arrives at your doorstep.

Via Reddit