Lecture-08: Liquid Crystal Display (LCD) (CGA)

 Liquid Crystal Display (LCD)

An LCD (Liquid Crystal Display) is a flat-panel display used in devices like laptops, TVs, calculators, and mobile phones.

It controls light using liquid crystals instead of emitting light directly.

Construction of LCD:

An LCD is made of several layers:

1.    Two Polarizers

o   One at 0° and another at 90°

o   They control the direction of light

2.    Glass Sheets

o   Two transparent glass plates hold the structure

3.    Transparent Electrodes

o   Made of Indium Tin Oxide (ITO)

o   One is positive (+) and the other is negative (−)

4.    Liquid Crystal Layer

o   Sandwiched between glass plates

o   Molecules can change orientation when voltage is applied

 

⚙️ Working Principle of LCD

🟢 Case 1: No Applied Voltage (OFF State)

• Light passes through first polarizer
• Liquid crystals twist the light (90°)
• Light passes through second polarizer
• 👉 Pixel appears bright (ON)

 

🔴 Case 2: With Applied Voltage (ON State)

• Electric field aligns liquid crystal molecules
• No twisting of light occurs
• Light is blocked by second polarizer
• 👉 Pixel appears dark (OFF)

 

🔢 Segment Display (From Image)

• LCD can form numbers using segments (A, B, C, D, E, F, G)
• Each segment is controlled by electrodes
• Example:
• Turn ON specific segments → display digits like 0–9

✅ Advantages

• Low power consumption 🔋
• Thin and lightweight 📱
• Less heat generation
• Good image quality

 

❌ Disadvantages

• Limited viewing angle
• Slower response than some displays
• Needs backlight

                                           Figure: Liquid Crystal Display