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Best Practices for Using A TFT Touch Screen

Views: 314     Author: Reshine     Publish Time: 2023-11-17      Origin: Site


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Best Practices for Using A TFT Touch Screen

TFT LCD touch displays are increasingly being used in devices ranging from consumer electronics to industrial and medical equipment. While design concepts for the use of TFT touch displays are well established, engineering and product design teams frequently encounter difficult-to-solve problems. Following best practices for using a TFT LCD touchscreen can save you a lot of "hair-pulling."

1. Installation of a TFT LCD Touch Screen

Ascertain that there is sufficient space (with a cushion) between the product housing and the TFT LCD screen.

When installing a TFT LCD module, make sure it is not twisted, warped, or bent.

1.1 CTP Bezel Mounting

CTP Mounting with bezel

The bezel window should be larger (>0.5mm) than the active area of the capacitive touch panel.

Between the bezel and the CTP surface, insulated gaskets (0.511mm) should be installed.

Further brackets For slim-type TFT LCDs, back support brackets are recommended.

1.2 Surface CTP Mounting

CTP Surface Mounting

The TFT LCD is attached to the countersink area with double-sided adhesive.

A gap (>0.3mm) between the product housing and the LCD cover lens is recommended.

Backside support with a gasket should be used when necessary (for example, on a TFT touch screen without a mounding structure).

CTP surface mount tft

Engineers should re-check the CTP specification for acceptable material and thickness if an additional cover lens is required.

A gap of 0.2–0.3 mm is required between the TFT LCD surface and the cover lens.

The cover lens window should be larger (>0.5mm) than the active area of the TFT touch screen.

1.3 RTP Installation

RTP Mounting

The TFT LCD touchscreen surface and the bezel must have a 0.2–0.3 mm space between them.

To prevent the user from pressing the RTP ITO Film connection, the bezel should cover the TFT LCD screen view area by at least 0.5mm (B).

Give the side of the TFT touch display and the bezel side wall a space of 0.2–0.3 mm.

Design Best Practices on the Ground

A variety of issues can arise if the ground approach used for a device with a TFT touch display does not adhere to best practices. Common grounding difficulties include:

Poor noise immunity, with interference affecting device operation

Long-term drift occurs when voltage changes degrade display performance over time.

In general, two key considerations are to keep ground connections as short as possible and to keep impedance to a minimum. This is especially important for ground connections between the display housing and the touch controller. The diameter of the ground connection has an impact as well, though it is less significant than the length.

Another important aspect of grounding design is avoiding ground loops. For ground distribution, a star topology can prevent a situation in which two points that are both intended to be on the ground have potential between them.

Any floating conductive parts near the touch sensor can cause erratic touch function behavior. As a result, they should all have the same ground potential as the touch controller.

2. Explained: How TFT LCD Works

When compared to standard LCDs, TFT LCDs provide very sharp and crisp images and text with a faster response time. TFT LCDs are being used in an increasing number of applications to improve the visual presentation of products.

2.1 TFT LCD Structure

The term "Thin Film Transistor" (TFT) is an abbreviation for "Thin Film Transistor." The transistors in the color TFT LCD display are made of thin films of amorphous silicon deposited on glass. It acts as a control valve, supplying a suitable voltage to liquid crystals for individual sub-pixels. As a result, TFT LCD displays are also known as Active Matrix displays.

Structure of TFT LCD

A liquid crystal layer separates a glass substrate with TFTs and transparent pixel electrodes from another glass substrate with a color filter (RGB) and transparent counter electrodes in a TFT LCD. In an active matrix, each pixel is paired with a transistor that includes a capacitor, which allows each sub-pixel to retain its charge rather than requiring an electrical charge to be sent each time it needs to be changed. TFT LCD displays are, therefore, more responsive.

TFT LCD displays

2.2 TFT LCD Operating Principle

To comprehend how TFT LCD works, we must first comprehend the concept of a field-effect transistor (FET). A FET is a type of transistor that controls the flow of electrical current using an electric field. It consists of three terminals: source, gate, and drain. FETs control current flow by applying a voltage to the gate, which changes the conductivity between the drain and the source.

TFT LCD Driving Principal

Using FETs, we can build the circuit shown below. The Data Bus sends a signal to the FET source, and when the SEL SIGNAL applies voltage to the gate, the driving voltage on the TFT LCD panel is created. A sub-pixel will be illuminated. Thousands or millions of such driving circuits can be found on a TFT LCD.

Drive TFT

2.3 Conclusion

To address those issues, you must challenge yourself. With a deep bench of expertise and 10+ years of experience in the TFT LCD industry, Reshine provides guidance and the ability to accelerate your time to market.

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