OLED basic and ICs

OLED, low cost modules for embedded and standalone

OLED (Organic Light Emitting Diode) is the technology that promises to revolutionize the next future display systems market. The most recent estimate revenues of 7 billions of dollars can be reached by 2017. The OLED display consist of (see Figure 1) a thin film of organic compound (typically polymers or small molecules, such as conjugated dendrimers or organometallic chelates) enclosed between two electrodes, one of which is transparent.

OLED structure
Human hair is 200X the thickness of the OLED layers

When current flows in the film, you induce excitation and decay phenomena in the unoccupied molecular bands, more or less the same way what happens with electrons and holes in the valence and conducting bands of inorganic devices when they are biased. The device emits so light in the visible spectrum.

The main advantages of OLED technology include a low response time that allows you to achieve high screens refresh rate, a higher contrast ratio and a more wide viewing angle compared to LCD devices, a lower power dissipation.

Oleds can also be planted on substrates of virtually any type, allowing, for example, to realize rigid-flexible display. The main disadvantages are the lower lifetime, color balance and burn-in problems, with a not uniform degradation of screen brightness at different frequencies of light which leads, over time, to a predominance of some component of color in the image reproduced. In addition, because of the difficulties in making economical large screen production processes, OLED technology was first available on the market solely for small screens, typically up to 7″, finding main use in portable devices such as mobile phones, PDA, gaming consoles and video cameras. The first 42 inch OLED TVs were marketed in 2012. In this regard, it should be noted that LED TVs have nothing to do with the OLED technology. They are in fact based on LCD screens using LEDs rather than traditional fluorescent sources for light in backlight panels, thereby improving the quality of the picture to the point of being comparable to that of plasma devices.

Modules

4D Systems is an Australian company rather known for its smart display modules. The following describes in particular the main solutions available from the company for the production of low resolution/cost OLED display which can be used in the most common embedded equipment. All modules include a OLED display and a graphics processor for its control.

Devices μOLED-96-G1 (SGC), μOLED-128-G1 (SGC) and μOLED-160-G1 (GSC), employ a passive matrix type screen. The module μOLED-160-G1 (SGC) (Figure 2), for example, supports a 1.7″ panel with an active area of 33.6 x 27 mm and a resolution of 160×128 pixels. The screen has a brightness of 100 cd/m2 and a contrast ratio of 5000:1; the viewing angle is greater than 160°. All three versions adopt the graphics processor GOLDELOX (SGC) that has a serial port for communication to the host. In addition to this, there are also available a reset line, 5 inputs with pull-up resistors that can be connected to switches, joystick or buttons and an audio output, capable of driving a classic low impedance speaker. There is also a slot for micro-SD memory cards with capacity up to 2 GB and micro-SDHC.

The supply voltage is 5 V; a 3.3 V line, derived from this, with current capacity up to 50 mA is also availbale and can be used to power external interface circuits. The graphics processor can be controlled, as said, using serial port. Among the main supported commands there are those of generic type, graphic, text and those for low-level access to memory uSD/uSDHC; the processor can also perform scripts in a dedicated language called 4DSL. Among the main features of highest level available, they include the ability to upload pictures from SD memory card and display them on the screen, draw geometric figures or icons and superimpose text strings.

μOLED-96-G1(SGC)
μOLED-96-G1(SGC)

The series μOLED-3202x-P1 is based instead on the graphics processor PICASO (SGC) and utilizes active matrix OLED 2.83″ or 2.4″ size, thus supporting images in standard resolution up to QVGA (240 x 320 pixels). The display μOLED-32028-P1T module is even equipped with touch-screen functionality. The graphics processor PICASO has serial interface as the GOLDELOX (SGC) and a micro-SD/micro-SDHC memory port. It can, however, access the memory using a standard file system like FAT16 (DOS), so resulting able, for example, to play WAV files. Audio output supports a PWM control and includes an amplifier and one 8Ω speaker. Sixteen general-purpose lines are also available (of which 8 can be used for making a fast data transmission parallel interface) and an interface for managing resistive 4-wire touch-screen panels.

The GFX series for standalone applications

The same modules μOLED-xx-G1 and μOLED-3202x-P1 are also available in GFX based GOLDELOX (GFX) and PICASO (GFX) processors, which differ from the corresponding series SGC for a different native firmware. This implements in the physical device a virtual processor named EVE (Extensible Virtual Engine) that can run applications in the proprietary language 4DGL. This way, the modules do not require a host processor for control and configuration but can be used in stand-alone applications. Alternatively, you can choose to code complex graphics features in 4DGL language so that they are executeded by graphics processor in response to a single statement sent by the host, thus reducing the computational load required to it for display management.

The language 4DGL inherits many basic features of popular programming languages like C, Basic or Pascal making available classical statements like If-Else-Endif, While-WEnd or Repeat-Until. It is so easy and quick to learn. To traditional instructions, however, it adds other more specific ones, for example, for the management of graphic objects. Also, some complex math functions (such as sine, cosine, and square root) are supported and so instructions for dynamic memory allocation. 4DGL-Workshop3 IDE is an integrated environment with editor, compiler and linker for 4DGL applications. It integrates a downloader that allows you to copy the compiled application from PC to the flash memory module. The module μOLED-3202x-P1 (GFX) based on PICASO-GFX2 processor (Figure 2), for example, integrated up to 15 KBytes of flash memory for code and up to 14 KBytes of SRAM memory for data/program.

4D Systems Picaso processor
Figure 2. 4D Systems Picaso processor

Besides the common features, the SGC version also has a second communications serial line , a master I2C port and eight 16-bit timers with 1ms resolution. In the end, a 2×30 pin header facilitates the connection of any expansion cards.