Liquid Crystal Displays (LCDs) employ various display modes, each with unique pixel structures and design intricacies. The most common modes include:

• Twist Nematic (TN) Mode: Known for its fast response times and cost-effectiveness, TN mode is widely used in consumer electronics.

• Vertical Alignment (VA) Mode: Offers better contrast ratios and deeper blacks, making it suitable for high-definition displays.

• In-plane Switching (IPS) Mode: Renowned for superior color accuracy and wide viewing angles, IPS is favored in professional monitors and high-end smartphones.

• Fringe Field Switching (FFS) Mode: Similar to IPS, FFS provides excellent color reproduction and wide viewing angles, often used in mobile devices.

Despite similarities in naming, each display mode features distinct design details and manufacturing processes.

Principles of Liquid Crystal Display Light Valves

LCDs are non-emissive displays; they control light passing through them rather than generating light. The grayscale and brightness of the display image are achieved by altering the liquid crystal molecules’ light valve effect, which changes the transmittance of incident light. As the orientation of liquid crystal molecules shifts, the amount of light passing through also changes. By applying different data signal voltages, the orientation of liquid crystal molecules is manipulated to display images in varying gray levels.

Controlling Transmittance with Liquid Crystal Orientation

The key to controlling an LCD’s light transmittance lies in adjusting the angle between the liquid crystal molecules’ long axis and the polarizer. The transmittance is zero when the angle is 0°, corresponding to the darkest state. At an angle of 45°, the transmittance is at its maximum, corresponding to the brightest state.

Normal White and Normal Black Modes

LCDs operate in either normal white (NW) or normal black (NB) modes, determined by their initial state without applied voltage:

• Normal White (NW) Mode: In the initial state without voltage (off-state), light can pass through the liquid crystal cell. A typical example is the TN mode. When voltage is applied, the liquid crystal molecules align vertically, blocking light passage and creating the off-state.

• Normal Black (NB) Mode: In the initial state without voltage (off-state), light cannot pass through the liquid crystal cell. Examples include FFS, IPS, and VA modes. Applying voltage reorients the liquid crystal molecules, allowing light to pass through and create the on-state.

Detailed Differences in Display Modes

Even within the same display mode, differences in design details and implementation processes can significantly impact performance:

• TN Mode: Fast response times and high refresh rates are achieved through the twisting of liquid crystal molecules, which quickly change alignment with applied voltage.

• VA Mode: Liquid crystal molecules align vertically to the substrates, providing superior contrast by blocking more backlight in the off-state.

• IPS Mode: Liquid crystal molecules align parallel to the substrates, resulting in wide viewing angles and better color stability.

• FFS Mode: Similar to IPS, FFS aligns liquid crystal molecules in a plane parallel to the substrates but uses fringe electric fields to achieve better light utilization and energy efficiency.