• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Electrical Engineering News and Products

Electronics Engineering Resources, Articles, Forums, Tear Down Videos and Technical Electronics How-To's

  • Products / Components
    • Analog ICs
    • Connectors
    • Microcontrollers
    • Power Electronics
    • Sensors
    • Test and Measurement
    • Wire / Cable
  • Applications
    • Automotive/Transportation
    • Industrial
    • IoT
    • Medical
    • Telecommunications
    • Wearables
    • Wireless
  • Resources
    • DesignFast
    • Digital Issues
    • Engineering Week
    • Oscilloscope Product Finder
    • Podcasts
    • Webinars / Digital Events
    • White Papers
    • Women in Engineering
  • Videos
    • Teschler’s Teardown Videos
    • EE Videos and Interviews
  • Learning Center
    • EE Classrooms
    • Design Guides
      • WiFi & the IOT Design Guide
      • Microcontrollers Design Guide
      • State of the Art Inductors Design Guide
    • FAQs
    • Ebooks / Tech Tips
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • 5G

The difference between LED and OLED displays

January 19, 2022 By dherres

Despite some initial difficulties, it is reasonable to think that OLED (organic light emitting diode) displays will replace LCDs, making possible low-power flexible screens relatively inexpensive to manufacture. OLEDs have several advantages. For one thing, they can be made onto a suitable substrate by means of silk screen-printing or an inkjet printer. Roll-to-roll vapor deposition methods permit economical mass production of OLEDs. The downside for now is that multi-layer devices have registration problems, i.e. lining up printed layers to the required degree of accuracy.

OLEDs lend themselves to production on flexible plastic substrates, facilitating development of new applications such as roll-up displays embedded in fabric or built into curved walls. Compared to LCDs, OLEDs exhibit a superior contrast ratio and wider viewing angle because the pixels emit light directly. The black level is deeper because a black OLED emits no light. (LCDs filter the light from dark areas, so there is no absolute black, except in recent models, which turn off the LED backlighting to create a perfectly black screen.) An inactive OLED element does not consume power. And OLEDs render superior video because they have a faster response time compared to LCDs.

Currently there remain some disadvantages when it comes to TV displays, including above all limited lifetime. A typical OLED TV panel after 1,000 hours experiences a 12% blue luminance degradation with 7% red and 8% green reduction. In comparison, LCDs have 25,000 to 40,000 hour ratings to half brightness. (A point to note: TVs advertised as LED TVs–not OLED TVs–actually have LCD technology. The LEDs provide backlighting instead of traditional cold-cathode fluorescent backlights. LED-backlit displays use the same TFT LCD technologies as CCFL-backlit LCDs.)

OLED schematicAn OLED generates light via a mechanism that differs from that of ordinary LEDs. Ordinary LEDs are comprised of a semiconductor material, usually a GaN compound, that releases energy in the form of photons when electrons in the semiconductor recombine with electron holes. The color of the LED light (corresponding to the energy of the photons) is determined by the energy electrons need to cross the band gap of the semiconductor. A layer of light-emitting phosphor often sits on the LED semiconductor to produce white light.

LG OLED tv combo
OLED displays range from the LG OLED TV, which goes for a mere $4,000, to simple OLED display modules for the Arduino which communicate with the MPU via an I2C interface.

In contrast, OLEDs contain organic material between their anode and cathode. For OLEDs on plastic substrates, the organic material is a version of the polymer poly(p-phenylene vinylene). The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of ordinary semiconductors. In addition, OLEDs often contain a special conductive layer of material chosen to aid charge injection at electrodes. This material is typically PEDOT:PSS, used because its HOMO level generally lies between the work function of ITO, which typically serves as the OLED’s transparent anode, and the HOMO of other commonly used polymers, reducing the energy barriers for hole injection. Metals such as barium and calcium are often used for the OLED cathode as they have low work functions which promote injection of electrons into the LUMO of the organic material.

Electrical current flows through an OLED from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. The withdrawal of electrons at the anode may also be described as the injection of electron holes into the HOMO. Electrostatic forces bring the electrons and the holes toward each other. They recombine to form an exciton, a bound state of the electron and hole. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation having a frequency in the visible light region. The frequency of this radiation depends on the band gap of the organic material, in this case the difference in energy between the HOMO and LUMO.

There are two types of OLED display modules. They are differentiated by how the OLED display is powered. PMOLED, for Passive-Matrix OLED, uses a simple control scheme in which each row (or line) in the display is sequentially lit (one at a time). PMOLED electronics do not contain a storage capacitor and so the pixels in each line are actually off most of the time. To compensate, the display power supply produces a voltage high enough to make the OLED pixels brighter.

PMOLEDs are inexpensive and also restricted in resolution and size (the more lines in the display, the more voltage necessary). PMOLED displays are usually small (up to 3 in typically) and are used to display characters or small icons. They typically are found in wearable devices and small appliances like hand tools.

 

oled driver ic
An example of an OLED display driver IC. This one is from Raydium Semiconductor Corp. and handles 480×480 RGB OLED displays using a DSI serial interface.

The AMOLED (or Active-Matrix OLED) display consists of a matrix of OLED pixels deposited or integrated onto a thin-film transistor (TFT) array. The TFTs generate light upon electrical activation and function as a series of switches to control the current flowing to each individual pixel. Typically, this continuous current flow is controlled by at least two TFTs on each pixel, one to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel and eliminate the need for the high currents as necessary for PMOLEDs. AMOLED displays consume the zero power with a black screen and the most power with a white screen. Thus AMOLEDs consume less power than PMOLEDs, have faster refresh rates and make possible larger displays with higher resolutions. Smartphones, digital cameras, and OLED TVs are all AMOLED devices.

Both types of OLED displays require a relatively high voltage (usually around 12 V) but a relatively small current (usually less than 100 mA).

When it comes to using OLED displays, the electrical interface of an OLED display module is generally a lot like the interface for an LCD or LED matrix. Display modules using all these technologies typically either accept conventional digital inputs or incorporate widely used serial interfaces such as I2C. More sophisticated OLEDs generally use a DSI serial interface

You may also like:


  • Quantifying and measuring non-electrical phenomena – Light

  • How to measure display screen output
  • displays
    Making sense of displays: OLED, AMOLED, POLED, PMOLED and T-OLED

  • Display options for MCUs: LCD, LED, and OLED
DesignFast Banner version: 03e68ea8

Filed Under: Featured, Test and Measurement Tips Tagged With: FAQ

Primary Sidebar

EE Training Center Classrooms

EE Classrooms

Featured Resources

  • EE World Online Learning Center
  • CUI Devices – CUI Insights Blog
  • EE Classroom: Power Delivery
  • EE Classroom: Building Automation
  • EE Classroom: Aerospace & Defense
  • EE Classroom: Grid Infrastructure
Search Millions of Parts from Thousands of Suppliers.

Search Now!
design fast globle

R&D World Podcasts

R&D 100 Episode 7
See More >

Current Digital Issue

Our second 5G Handbook is now available

Featuring 15 articles, the 2022 5G Handbook looks at private networks, timing, connectivity, latency, mmWaves, test, and other topics.

Digital Edition Back Issues

Sponsored Content

Positioning in 5G NR – A look at the technology and related test aspects

Radar, NFC, UV Sensors, and Weather Kits are Some of the New RAKwireless Products for IoT

5G Connectors: Enabling the global 5G vision

Control EMI with I-PEX ZenShield™ Connectors

Speed-up time-to-tapeout with the Aprisa digital place-and-route system and Solido Characterization Suite

Siemens Analogue IC Design Simulation Flow

More Sponsored Content >>

RSS Current EDABoard.com discussions

  • A circuit that can adjust a resistance and probing a voltage node
  • DC to DC buck converter
  • A circuit that can probe 2 currents and adjust the resistor
  • Microsoft Project 2019 dependencies
  • MOSFET ORing circuit simulation (LTspice)

RSS Current Electro-Tech-Online.com Discussions

  • Enclosure sought
  • Need help using a common power supply for two devices
  • Fletcher's Law
  • Setting the 18F24K20 to digital.
  • Multistage BJT amplifier

Oscilloscopes Product Finder

Footer

EE World Online

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDABoard Forums
  • Electro-Tech-Online Forums
  • Engineer's Garage
  • Microcontroller Tips
  • Power Electronic Tips
  • Sensor Tips
  • Test and Measurement Tips
  • Wire & Cable Tips

EE WORLD ONLINE

  • Subscribe to our newsletter
  • Lee's teardown videos
  • Advertise with us
  • Contact us
  • About Us
Follow us on TwitterAdd us on FacebookConnect with us on LinkedIn Follow us on YouTube Add us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy