This document provides an in-depth analysis of projected capacitive touch screens, including how they work, their structure, and differences in types. It discusses how projected capacitive touch screens use two perpendicular sensing arrays to detect touch locations. The structure generally involves a cover lens and sensor, which can be constructed in different ways, such as G/G (glass/glass), G/F (glass/film), or G/P (glass/PET). The main difference between types is whether the lens is glass or film. Concave touch screens are most common due to their low-cost single ITO layer glass sensor with a printed film.

1. Capacitive Touch Screen Type---SYMPHONY
A-Z knowledge about tablet PC capacitive touchscreen: an in-depth analysis for touch panel
variations of G+G, G+F, G+P and concave touchscreens
This report consists of the following 3 parts:
1. How does projected capactivie touchscreen work ?
2. Stack / Structure of Projected capactive touchscreen
3. What’s the difference bewteen G+G, G+F, G+P and concave touchscreens ?
How does projected capactivie touchscreen work ?
Figure 1: How capacitive touchscreen works
The projected capacitive touch screen works on the principle of conventional capacitive touch screens
with the addition of two sensing arrays (X and Y as shown in Figure 6) on two different layers that are
perpendicular to each other along with a drive line. As X and Y arrays exist on different layers, the point
where the two intercept becomes a capacitive node. When electrical currents run along one of the arrays
through the drive line, the other array and the circuitry that detects change in capacitive values becomes
connected. During actual operation, the controller sends electrical currents to the drive lines on different
layers to create a specific electrical field with the nodes.

2. Capacitive Touch Screen Type---SYMPHONY
Figure 2: work flow of touch action of capacitive touchscreen
Since human body is a conductive organ, When the user places his finger or uses a touch medium to the
touch screen, coupled capacitor is thus formed, the controller immediately picks up the change in
capacitive value between the nodes and drive lines to pinpoint the exact location of the touch event.
Now we know what’s the projective capacitive touchscreen ? However, we need to dig deep to learn
more about the structure and function process of every component that makes up of capacitive
touchscreen.
Stack / Structure of Projected capactive touchscreen:
Figure 3: Structure of projected capacitive touchscreen
Generally, projected capacitive touchscreen consists of cover lens and sensor, but they may be of
different constructions due to different requirements either on application or cost, the following chart
shows the comparison of different contructions:

3. Capacitive Touch Screen Type---SYMPHONY
Structure Characteristic Transmissibility
G/G High reliability >90%
F/F/Lens More thin >90%
G/Lens
The same strucuture to
iPhone
>90%
F(G) / Lens (Single ITO
layer )
More thin, lower cost >90%
Lens Materials Thickness Spec. Recommended
Harden Glass ( Tempered
glass )
0.5mm, 0.6mm, 0.7mm, 0.8mm, 1.0mm
PMMA / PC 0.65mm, 0.8mm
PET 0.188, 0.125mm
Figure 4: Different construction
Let’s look into G/G type of projected capacitive touchscreen, we need to know the ITO sensor
construction.

4. Capacitive Touch Screen Type---SYMPHONY
Figure 5: ITO sensor construction, source: 3M
Figure 6: Structure of sensor layer and electrode pattern

5. Capacitive Touch Screen Type---SYMPHONY
Figure 7: Mutual Capacitance Rows and Columns
Figure 8: capacitive sensing
Sensor grid in diamond patterns are printed on the ITO sensor. As shown above.
Mutual capacitance is the intentional or unintentional capacitance between two "charge holding objects."
Projected capacitance touchscreens intentionally create mutual capacitance between ele¬ments of
columns and rows [see figure 8] in the vicinity where each intersect the other. This allows the system
electronics to measure each node (intersection) individually to detect multiple touches on the screen
during one screen scan.
When a finger touches near an intersection, some of the mutual capacitance between the row and
column is coupled to the finger which reduce the capacitance at the intersection as measured by the
consystem electronics. This reduced capacitance crosses the "touch threshold" set by the electronics
indicating a touch has occurred.

6. Capacitive Touch Screen Type---SYMPHONY
What’s the difference bewteen G+G, G+F, G+P and concave touchscreens ?
Firstly, we need to know the first letter refers to sensor part, while the latter refers to lens(cover).
Then, from the meaning of the words, we know G+G means glass type sensor part and glass type of lens
(cover), for most of tablet PC now, glass type sensor is made with SITO, means two ITO sensor layers
are housed in one single side of the sensor glass with an isolation layer in between.
G+F type of capacitive touchscreen employs single ITO layer glass sensor and printed film as lens(
cover), likewise, G+P uses PET as lens (cover).
Concave touchscreen as one type of G+F, is the most popular low-cost solution due as it only needs a
printed film on the sensor glass, in this way, the defective rate of this type of touchscreen is very high(
no need other process with lens )
Figure 9: G+G capacitive TP Figure 10: concave touch screen