E Ink released the Carta e-paper screen in 2013 and Carta HD in 2015. Both of these technologies rely on the Regal Waveform Controller. Regal virtually eliminates the need for a full refresh, giving the viewer smoother viewing transitions and prevents ghosting. This enhances the reader’s experience by providing smoother page turns and more focused reading. There are no technical details on how Regal works and this is by design, Regal and the other waveforms on the market are a closely guarded secret that is not shared with anyone, except under an NDA.

You might not have heard the term before but “waveforms” are software based and control the transition from different state changes on the screen. In order to understand how they work, you need to understand what an E Ink screen does and how waveforms effect it.

An e-ink display is a fairly weird beast, mainly because of how it works. Basically, the display logic itself consists of a shift register to select a row of pixels, plus a ‘shift register’ you can load with 8 bits at a time to clock in the pixel values for the selected row. This shift register has two bits per pixel, to select if a pixel should go black, go white or stay the same. By shifting display changes like that through all the rows, you can partially or fully replace the image that’s on the screen.

Because the display works with electrophoretic ink particles, it needs a fairly high voltage to attract and repel them. For example, a generic off the shelf e-paper display from Ebay needs +15V and -15V These voltages are switched with two MOSFETs per pixel, and these need a gate voltage that’s more than the positive and negative 15V: on this display, +22 and -20 volts are required. The display also needs a standard 3.3V power rail for its logic, and a display-specific Vcommon voltage of about -1 to -3 volts.

On a programming level in order to go from white to black, it can be accomplished in 4 clock cycles in the form of 0b10 0b01 0b01 0b01, to go from grey to darker grey, the table can be something like 0b01 0b01 0b10 0b01, etc (it is an example, in general it is about 20 or 40 cycles).

The only two types of waveform controllers that I am aware of – Regal and A2 mode, which is really called dithering. Regal is the most popular one because it is used on virtually all of the mainstream e-readers such as the Kindle Paperwhite, Kindle Oasis, Nook Glowlight 3, Kobo Aura One and Kobo Clara HD.

The exact implementation of Regal on these e-readers depends on the internal construction and what type of temperature is being generated, cables and even the size of the screen. Each model has a slightly different variation and the implementation is different whether the device is employing an IMX.6 Solo Lite or IMX.7 dual core processor. I have found from my research that if an e-reader is using a Freescale/NXP processor it is going to be using Regal.

The Onyx Boox Note, Boyue Likebook Mars and Icarus Illumina XL6 use an E Ink Carta screen, but instead of using Freescale processors they use generic quad-core or octa-core processors. Their technical specifications make no reference to Regal. This is likely why all of these models employ A2 mode, which enables faster page refreshes, but somewhat degrades the image quality. It is a workaround that emulates the best aspects of Regal, but the engineering team working at these e-reader companies have better flexibility to refine the process.

Are A2 and Regal the only waveform controllers that exist and is there any documentation? In a statement E Ink told me “The specifics about how exactly our waveforms work is something my IP department will not allow me to share. When we engage with a new customer, we do share information about waveform options that are available for their product, but this is all done under an NDA. These are software-based and have been developed by our in-house engineers specifically for our materials. Different hardware could perform differently between types of waveforms, in that the communication protocols are different, but choices about refreshes often are a balance of speed, functionality and energy consumption, and our customers make the final decision about the waveform they will use.”

The lack of forthcoming information on waveform controllers is why Google is a barren wasteland when you try and find technical documentation, simply because none exists. The only things that are available are specific waveform files that venders send you when you order the E Ink display from their website. No OEM’s or companies that make white labeled e-readers for brands in Europe and China would also comment on it.

