How to Improve LCD Viewing Angle


LCD Viewing Angle Definition

Orient Display: LCD Viewing Angle Definition

Fig.1 LCD Viewing Angle Definition

The view direction is the right direction marked with Φ which is with respect to the X-axis. The original location is the center point of the display panel surface, the Z axis is Normal, the X-axis is Horizontal and Y-axis is Vertical.

Normally it was defined 4 angles to correspond with 3, 12, 9, and 6 o’clock respectively. So, you can find the 6 o’clock or 12 o’clock parameter in the LCD datasheet.

Viewing Angle is the angle with respect to the Z-axis in a certain direction and marked by θ (θU means upper View Angle). Viewing Angle describes the maximum watching angle and it is one of the key indicators with the display module.

The viewing angle can also be explained using the simple way as below.

The bias angle is the angle perpendicular from which the display is best viewed. (See Fig.2) This angle is determined when the display is designed and can be set at any angle or orientation. The orientation of the bias angle of a LCD display is often stated with reference to a clock face. If the offset is above the display, it is referred to as a 12:00 or Top view.

Orient Display: LCD Viewing Angel Definition (Side Views)

Fig.2 LCD Viewing Angel Definition (Side Views)

How to Improve LCD Viewing Angle

The viewing angle is the angle formed on either side of the bias angle, where the contrast of the display is still considered acceptable. Generally, this contrast is specified as 2:1 for monochrome LCD and 10:1 for color LCD. A typical STN character display running at a duty cycle of 1/16 has a viewing angle of ±20 degrees and a bias angle of 25 degrees. For example, assume the display is a 12:00 (topview) type. When the display is viewed from 25 degrees above the vertical, it will be at its maximum contrast and best look. If the viewer moves their eyes further above the display by an additional 30 degrees, they will see a contrast reduction, but the display will still be readable. Moving the view position any further above the display will reduce the contrast to an unacceptable degree.

Normally, we have the ways below to improve the viewing angle.

  • Voltage Adjustment to optimize the contrast

Adjusting the contrast voltage, VL, effects the Bias Angle to some extent, but not the Viewing Angle. A top view 12:00 display can be optimized for a bottom view 6:00 viewing position by adjusting the contrast voltage. A 12:00 display set for a 6:00 viewing position will not have as great a contrast as a 6:00 display set for 6:00 viewing position and vice versa.

Generally, displays are optimized for straight-on viewing. Either a 6:00 or 12:00 module may be used and the contrast voltage can be adjusted slightly to optimize the display for that viewing position. In the above example, the viewing angles of both 6:00 and 12:00 modules actually overlap the perpendicular (or straight on) viewing position.

  • Contrast Adjusting

When the view position is established, the contrast setting can then be determined. This is done during product development on the prototyping units. Generally, a 10K ohm potentiometer is then connected between VDD and VSS in a single supply module, or from VDD to the negative rail in a dual supply module. The wiper of the pot is connected to the VL input of the module. (See Fig.3) The LCD is positioned at the nominal viewing position and the pot is adjusted to obtain the desired LCD appearance. The voltage on the VL pin is now measured and a pair of resistors are chosen to produce this voltage in the production units.

Orient Display: Contrast Adjustment

Fig.3 Contrast Adjustment

By adjusting driving voltage and contrast is the most cost-effective way to improve the viewing angle. Different viewing angles need different driving voltage. It is compromising. In discussing the best viewing angle, we have to fix the voltage angle first.

  • Changing LCD Design

    • If possible, try to design the driving multiplex (duty ratio) as small as possible. Static drive has the best contrast.
  • Using Better Polarizer

    • The higher the efficiency, the better of the contrast. It is especially important for negative display. Changing from 98% to 99.9% polarizer will do the work.
    • With ambient light, the more reflective of the polarizer, the better the contrast.
    • With backlight, the more transmissive of the polarizer, the better the contrast.
  • Choosing Right Liquid Crystal Material

    • The better K33/K11, the better steepness of V90/V10, the better the contrast.
    • The higher the voltage, the better K33/K11, the better the contrast (when V10 ≤ 2 volts)
  • Applying Premium Quality Orientation Layer (Polyimide)

    • Use high quality polyimide (Nissan Chemical)
    • Use high quality rubbing fiber and good quality rubbing equipment to make the liquid crystal molecular alignment uniform.
  • Changing Display Mode

    • Positive LCD to Negative LCD (When the LCD is used indoor or dark environment, the contrast will increase a lot, but it will not display well with ambient light only, it is also more expensive)
    • TN (Twisted Nematic) to VTN (Vertical Alignment)
    • Normal VTN (Vertical Alignment) to Wide Viewing Angle VTN.
    • TN (Twisted Nematic) to STN (Super Twisted Nematic)
    • STN (Super Twisted Nematic) to FSTN (Film Super Twisted Nematic)
    • Blue STN (Super Twisted Nematic) to Negative FSTN (Film Super Twisted Nematic)
    • Negative FSTN (Film Super Twisted Nematic) to FFSTN (Double Film Super Twisted Nematic)
    • Normal FFSTN (Double Film Super Twisted Nematic) to Wide Viewing Angle FFSTN
    • Negative FSTN (Film Super Twisted Nematic) to ASTN (Automotive Super Twisted Nematic) (especially when temperature changes).
    • FFSTN (Double Film Super Twisted Nematic) to TFT (Thin Film Transistor)
    • TN (Twisted Nematic) TFT to IPS (In-plane Switching) TFT
  • Straight on Viewing

    • For TN display, when multiplex is 4, some customers complain that the straight on viewing is not clear (perpendicular to the LCD). The solutions are:
        • Change the LCD from TN to HTN, 95% customers will be satisfied with the HTN LCD.
        • Re-design the LCD to make it 3 multiplex or even lower multiplex.
  • High Density LCD

    • When a LCD is high density with the segments/icons or very crowded, some customers also complains the viewing angle or contrast are not good. The reason is for crowded display, the layout can be long and thin. The voltage drop along the layout can be big. The solutions are:
        • Use low resistivity ITO glass to reduce the layout resistance.
        • Use STN or even FSTN to make the viewing angle/contrast tolerance bigger.

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