How LCD works
As in its name, Liquid crystal displays utilize Liquid Crystals, which exhibit both characteristics of solid and liquid. Applying an electric field can change LC molecular alignment temporarily, and thus modulate the polarization of light passing through. LCDs don’t emit light themselves so they need other light sources.
The optical configuration of an LCD, often referred to as a “sandwich” structure, typically includes a) a front polarizer or analyzer; b) a back polarizer, cross-positioned to the front one in terms of polarization; and c) a liquid crystal layer in between.
Depending on transmission modes of the “light modulator”, LCDs can be divided into three categories: transmissive, reflective, and transflective mode, as illustrated below. Note that back polarizers in these LCDs are transmissive, reflective, transflective types accordingly, while front polarizers are always transmissive to let modulated light through.
Schematic diagram of the (a) Transmissive mode, (b) Reflective mode, and (c) Transflective mode
Reflective LCDs utilize ambient light from a front source, usually the environmental light. Whereas transmissive displays rely on LED backlights to illuminate the surface. Featuring a combination of both reflective and transmissive characteristics, a transflective LCD can take advantage of both environmental ambient light and LED backlight at the same time.
All three transmission modes are used in the passive LCDs, whereas most TFT LCDs are transmissive types.
Learn more about viewing modes and applicable lighting conditions.
1Tan, M. T., Richey, R., & Layton, J. LCD Fundamentals and the LCD Driver Module of 8-Bit PIC Microcontrollers. 2018. Microchip Technology. Retrieved from http://ww1.microchip.com/downloads/en/AppNotes/AN658-LCD-Fundamentals-and-the-LCD-Driver-Module-of-8-Bit-PIC-MCUs-00000658C.pdf
IBN (VA) LCD
Schematic diagram of the (a) IBN (VA) mode and (b) TN mode
IBN (Improved Black Nematic) display adopts the vertical alignment switching mode commonly used in TFT displays, and applies it to passive driven LCDs.
As illustrated in the schematic diagram, the front and rear polarizers are cross-placed to each other in VA mode. In the voltage-off stage, liquid crystals are perpendicular to the glass surface, thus lending no help to change the polarization of light. Polarized light is blocked by the front polarizer with a different polarization, presenting a clean, black surface with little light leakage. When a high voltage is applied, liquid crystals twist to align in parallel with the surface, and guide polarization changes for the light passing through.
With little “bleed-through” and high transmission, our IBN technology is able to achieve a very high contrast ratio (>1000:1) in a negative mode.
Moreover, our IBN technology goes far beyond a simple, monochrome LCD display – we provide total solutions of color IBN and Hybrid IBN+TFT display!
BOE Varitronix Color IBN
BOE Varitronix Hybrid Color IBN (entire top) + TFT (center)
Color IBN utilizes a color diffuser layer with designated areas painted in colors. For applications where there is a pre-designed layout with colorful icons or segment, color IBN provides a crystal-clear image, super high contrast, and vivid colors – all at a “passive-LCD-level” cost and energy consumption.
When “inexpensive” and “partial dynamic content” appear on your LCD requirement list at the same time, Hybrid IBN+TFT display is here to save the day. Our hybrid solution combines a complete, free-shape IBN at the top, with a small sized, standard TFT at the bottom. Overall, it looks like one display with free content to display within the TFT area and on/off color segments for the rest of the screen. The hybrid solution provides a cost-effective way to achieve the features and performance you need.
STN LCD
Schematic diagram of the (a) DSTN LCD, (b) ISTN LCD, and (c) FSTN LCD.
Depending on enhancement methods and structures, the STN LCD family has a wide range of variations for different needs, such as “silver mode” and “blue mode” for background colors, FSTN with a compensation film, and DSTN with a dummy cell for anti-retardation over temperature changes.
To compliment with STN LCD and types beyond, we also offer ESTN (Enhanced performance STN) and ISTN (Intelligent STN) at BOE Varitronix. Their structures are shown in the image.
ESTN (Enhanced performance STN) is a low-cost alternative for DSTN or FSTN. ESTN is used in negative mode displays and can be optimized via the backlight color to increase higher contrast. They usually have a blue background. However, they are not suitable for a high-temperature environment.
ISTN (Intelligent STN) has a special temperature-compensating liquid crystal polymer (LCP) film to enable a good performance under temperature fluctuations. It’s commonly used in the automotive industry and can work for more than 15 years.
You may find those variations of STN LCDs quite confusing but worry not – we have summarized their features for you in this comparison table:
Types of STN Passive Matrix LCDs
| Type | FSTN | ISTN | DSTN | ESTN |
|---|---|---|---|---|
| Name | Film compensated STN | Intelligent STN | Double STN | Enhanced performance STN |
| Cost | Lowest cost | Medium-high | Medium | Low cost |
| Structure | Has a retardation film | Has a special LCP film | has a dummy cell | Alternative to DSTN |
| Feature | Compensate for the common yellow-greenish background | Very good performance under temp. fluctuations | Resilient to the retardation over temp. changes | Increase negative mode contrast Blue background |
| Application | Industrial Normal environment | Automotive Industrial | Automotive With Heater | Industrial Not too high temperature |
Type of Monochrome Displays by Application
Passive monochrome displays are widely used thanks to their simplicity – simple to design, manufacture, and read. Depending on display content and applications, passive monochrome display can present content in formats including:
- Segment (7-segment digit numbers and icons)
- Character (14 or 16-segment characters)
- Matrix (Pixel images and wave forms)
With the type of content to display in mind, you can refer to the table below on what capabilities of LCD to look for.
