Passive LCD vs. Active LCD

and PMOLED vs. AMOLED 

 

 

 

LCD (Liquid Crystal Display) and OLED (Organic Light Emitting Diode) are the most popular display technologies used for consumer, industrial, automotive, home appliance, IoT etc.  But there are some confusion between passive LCD vs active LCD and PMOLED (Passive Matrix OLED) and AMOLED( Active Matrix OLED). We will explain the differences as below. 

 

Passive LCD vs. Active LCD 

Passive Matrix LCD uses grid of vertical and horizontal conductors comprised of ITO( Indium Tin Oxide) to create an image. Each pixel is controlled by an intersection of two conductors. By creating a potential voltage difference at an intersection, the LC fluid is able to respond by creating an “on” state at that intersection, also commonly referred to as a pixel. Please see the structure of passive LCD as below.

Fig. 1 Passive Matrix LCD Structure

Active-Matrix LCD uses TFT (thin film transistors) that are arranged in a matrix on a glass surface. To control the voltage tiny switching transistors and capacitors are used at each pixel location. The active pixel is called so because it has the ability to control the individual pixels and switch them quickly. Please see the active matrix LCD structure below.

Fig. 2 Active Matrix LCD Structure

Fig. 3 Passive Matrix LCD and Active Matrix LCD Driving Comparison

 

Difference Between Passive Matrix LCD and Passive Matrix LCD

  Passive Matrix LCD Active Matrix LCD
Structure It uses grid of vertical and horizontal conductors comprised of Indium Tin Oxide to create an image. Each pixel is controlled by an intersection of two conductors. It uses thin film transistors that are arranged in a matrix on a glass surface. To control the voltage tiny switching transistors and capacitors are used at each pixel location.
Cost Lower Higher
Customization Flexible with lower cost Higher NRE with $100K to $1M
Contrast Ratio Lower Higher
Response time Slower Faster
Color Saturation Lower, not true color Higher
Resolution Limited to 320×240 with reasonable contrast Capable for much higher resolution, can produce 8K resolution now.
Gray scale Very limited Capable for high gray scale
Current Consumption Lower Higher
Application Low cost watches, calculators, utility meters etc. Mainly low cost, low power monochrome displays Laptop, monitor, mobile phones, TVs, ATM, Kiosk, Advertisement panels etc. Mainly color displays

 

PMOLED vs. AMOLED

OLEDs are made from organic light-emitting materials that emit light when electricity is applied. OLED displays are emissive. That is the reason that OLED displays do not require backlight or filtering that are used in LCDs. As a result, OLEDs can be made flexible and transparent while providing the best images and great contrast and view angles.

Similar to LCD displays having two types: Passive Matrix LCD and Active-Matrix LCD, OLED displays also has two types: PMOLED and AMOLED. The difference is in the driving electronics – it can be either Passive Matrix (PM) or Active Matrix (AM).

Similar to passive matrix LCD, a PMOLED display uses a simple control scheme in which you control each row (or line) in the display sequentially (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. Because of this ,more voltage is needed to make PMOLED brighter. If you have 10 lines, for example, you have to make the one line that is on 10 times as bright (the real number is less than 10, but that’s the general idea).

While PMOLEDs are easy and low cost to produce, they are not efficient and the OLED materials suffer from lower lifetime (due to the high voltage needed). PMOLED displays are also restricted in resolution and size (the more lines you have, the more voltage you have to use). PMOLED displays are usually small (up to 2″ in color and 6” in monochrome typically) and can be used in simple digits/icons, characters, alphanumeric and low resolution dot matrix application such as  a MP3 players, mobile phone sub displays, simple waist watch etc.

Fig. 4 PMOLED Structure

Similar to active-matrix LCD, an AMOLED (Active-Matrix OLED) is driven by a TFT (Thin Film Transistor) which contains a storage capacitor that maintains the line pixel states, and so enables large size (and large resolution) displays. AMOLEDs can be made much larger than PMOLED and have no restriction on size or resolution.

AMOLED panels started to emerge in the market in 2007. Because of its high cost, it is normally found applications of high end consumer products, such as mobile phones, cameras, tablets, laptops and TVs. Samsung and LG are dominant in producing AMOLED. Now, some manufacturers in China are trying to catching up but we believe it will still take several years for us to see AMOLED widely used in other applications. 

Fig. 5 AMOLED Structure

  PMOLED AMOLED
Structure Each row (or line) sequentially is controlled. PMOLED doesn’t have a storage capacitor and  the pixels in each line are off most of the time. Driven by a TFT (Thin Film Transistor) which contains a storage capacitor that maintains the line pixel states
Cost Lower Higher
Customization Flexible with reasonable cost Very high NRE , high volume needed
Contrast Ratio Good Excellent
Response time Excellent Excellent
Color Saturation Lower, not true color Higher
Resolution and size Limited to 320×240 , 2” for color and 6” for monochrome Capable for much higher resolution, can produce 8K resolution, 110” available in the market now
Life time Relatively Lower Can be higher
Current Consumption Lower Higher
Application Low cost watches, MP3, cell phone sub display Laptop, monitor, mobile phones, TVs,