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Archived - PowerBook Displays: Active Matrix and Passive Matrix Compared

This article compares active matrix and passive matrix LCD displays used in PowerBook and iBook computers.
This article has been archived and is no longer updated by Apple.
Liquid Crystal Display (LCD) is the technology used on the screens of PowerBook and iBook computers. LCDs are non-emissive (no extra low frequency (ELF) or very low frequency (VLF) emissions); they do not create their own light, but reflect and block light. LCDs use a reflector, backlight, sidelight, or a combination of a reflector and back/sidelight to display an image.

The main difference from a cathode-ray tube (CRT) display is that the pixel (the little dots of light that comprise the picture on a computer or TV screen) is not the source of light. A typical LCD consists of a reflector, rear polarizer, back glass, liquid crystal material, front glass, and front polarizer.

The liquid crystal material is a liquid with rod-shaped molecules inside. The rod-shaped molecules can form a twisting helix, or spiral pattern and bend light that enters the display. When electric current is applied, the rods straighten out and no longer bend the light. The inside surfaces of the glass are treated and polished to induce the rod-shaped molecules in the liquid crystal material to line up with the polarizers.

The display uses two polarizers to line up the light and reduce glare. If the light is out of phase, it can not pass through the polarizer. By using two polarizers 90 degrees out of phase with each other, the light is blocked. The liquid crystal material bends the light 90 degrees so it will pass through the polarizer. When the LCD has power to it, it does not bend the light, hence it does not pass through the polarizer.

This type of display is called an active matrix, or Thin-Film Transistor (TFT), display. Passive matrix, or Film SuperTwist Nematic (FSTN), displays are similar to TFT displays, but the liquid crystal molecules in a SuperTwist Display bend or twists light much farther than in a standard TFT display. In fact, the molecules in a SuperTwist display can bend 270 degrees or more to transmit light. One difference you may notice between passive and active matrix screens is that active matrix has a much wider viewing range than passive matrix. In other words, you can see information displayed on the screen from a wider side angle on an active matrix display than on a passive matrix display.

Passive Matrix

In a passive matrix, or FSTN, display a grid of electronic control wires or lines are placed on the front and back glass. A pixel is located at the junction of each row and column control lines. Passive matrix displays use one transistor to address each row and one to address each column of pixels. Pixels are turned on when both row and column lines are energized and off when both control lines are de-energized. This addressing scheme is called multiplexing.

The residual electrical current that travels down each control line can cause crosstalk at unselected pixels. Crosstalk partially darkens pixels and lowers the display's overall contrast. This usually appears on a passive matrix PowerBook display as two dark boxes, parallel to each other on the display.

Active Matrix

The active matrix, or Thin-Film Transistor (TFT) display is the latest technology used in Macintosh PowerBook computers. Rather than using multiplexing (row and column wires on the glass) techniques to address the matrix of crystals, the active matrix LCD includes a transistor fabricated along with each pixel. You can think of the display as one large Integrated Circuit (IC), with the transistors acting as switches to turn on individual pixels. (An IC is a slice or chip of material on which is etched or imprinted a circuit comprised of electronic components and their interconnections.) Because of the transistors, pixels can be turned on and off at a very fast rate. The transistor at each pixel eliminates the crosstalk phenomenon, which lowers contrast on an FSTN display.

The TFT method eliminates the time dependency associated with multiplexed displays by directly addressing each pixel.

The following charts which PowerBook models have active matrix or passive matrix displays:

PowerBook Model
B&W/Color/Grayscale
Display Type
100
B&W
Passive
140
B&W
Passive
145
B&W
Passive
145B
B&W
Passive
150
Grayscale (4 Grays)
Passive
160
Grayscale (16 Grays)
Passive
165c
Color (256 Colors)
Passive
170
B&W
Active
180
Grayscale (16 Grays)
Active
180c
Color (256 Colors)
Active
190
Grayscale (16 Grays)
Passive
190cs
Color (256 Colors)
Passive
520
Grayscale (16 Grays)
Passive
520c
Color (256 Colors)
Passive
540
Grayscale (16 Grays)
Active
540c
Color (256 Colors)
Active
1400cs
Color (thousands of colors)
Passive
1400 c
Color (thousands of colors)
Active
5300
Grayscale (16 Grays
Passive
5300c/100 8/500
Color (256 Colors) (2)
Active
5300c/100 16/750
Color (thousands of colors) (2)
Active
5300cs
Color (256 Colors)
Passive
5300ce
Color (thousands of colors)
Active
Duo 210
Grayscale (16 Grays)
Passive
Duo 230
Grayscale (16 Grays)
Passive
Duo 250
Grayscale (16 Grays)
Active
Duo 270c
Color (256 Colors) (1)
Active
Duo 280
Grayscale (16 Grays)
Active
Duo 280c
Color (256 Colors) (1)
Active
Duo 2300c
Color (256 Colors) (1)
Active
2400c
Color (thousands of colors)
Active
3400c
Color (thousands of colors)
Active
G3
Color (thousands of colors)
Active
G3 Series
Color (thousands of colors)
Passive
G3 Series
Color (millions of colors) (3)
Active
G3 Series (Bronze Kbd)
Color (millions of colors)
Active
G3 Series (FireWire)
Color (millions of colors)
Active
G4 - all models
Color (millions of colors)
Active
iBook - all models
Color (millions of colors)
Active

Notes:
    1. Thousands of colors in 640 by 400 resolution
    2. The PowerBook 5300c computer is available in two configurations. One model has 512K of built-in VRAM, the other has 1 MB.
    3. Also available in 30 cm STN passive display.
    4. Some of the descriptions in this table only apply to computers sold in the United States.
Last Modified: Feb 20, 2012
  • Last Modified: Feb 20, 2012
  • Article: TA21582
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