Multi touch technology, touch screen and touch screen controller are explained in detail
Author:Abarba Time:2021-06-07 16:52 Browse(822)

Multi touch technology, touch screen and touch screen controller are explained in detail

when two fingers touch, the movement direction of the two fingers can be recognized, but the specific position can not be determined, and the operation of scaling, translation, rotation and so on can be carried out.
this multi-point touch method is relatively simple.
axis coordinate method can be realized.
ITO is divided into X axis and Y axis.
two touch operations can be sensed, However, sensing touch and detecting the specific location of touch are two concepts.
the XY axis touch screen can detect the second touch.
but it is impossible to know the exact location of the second touch.
a single touch generates a single maximum value on each axis.
so as to determine the location of the touch. If there is a second finger touch screen, it can detect the second touch, There will be two maximum values on each axis.
these two maximum values can be generated by two groups of different touch.
therefore, the system can not accurately judge.
some systems introduce timing to judge.
it is assumed that two fingers are not placed at the same time, but there are always cases of touching at the same time, The system can't guess.
we can call the points that are not really touched as "ghost points.
recognizing the finger position multi touch all point is a popular topic recently.
it can recognize the specific position of the touch points.
the system can recognize the location of the touch pointsThat is, there is no "ghost spot" phenomenon.
multi touch recognition position can be applied to any touch gesture detection.
it can detect the simultaneous touch of ten fingers in both hands, and also allow other non finger touch forms, such as palm, face, fist, etc., even wearing gloves. It is the most humanized human-machine interface mode, which is very suitable for the application of multi hand simultaneous operation,

the scanning times, However, the multi touch all point detection method needs 150 times.
the multi touch all point detection method is based on mutual capacitance.
instead of self capacitance, the self capacitance detects the change of capacitance (parasitic capacitance CP) of each sensing unit, and the parasitic capacitance will increase when there is a finger, so as to judge the presence of touch, The mutual capacitance is to detect the change of mutual capacitance (that is, coupling capacitance cm) at the intersection of rows and columns. When rows and columns cross, mutual capacitance will be generated between rows and columns (including the edge capacitance between row and column induction units and the coupling capacitance generated at the intersection of rows and columns). When there is a finger, the mutual capacitance will decrease, and the existence of touch can be judged, And accurately determine the position of each touch point.
touch screen technology, the following is about touch screen.
touch screen.
simply speaking, input and output are combined, no longer need mechanical buttons or sliders, the display screen is the human-computer interface.
the whole touch screen module is composed of LCD.
LCDTouch screen, touch screen controller, main CPU, The LCD controller is composed of the touch screen and the touch screen controller, which are the core of the whole module.
so we will focus on these two parts.
the structure of the touch screen from top to bottom is: 1 surface shield; 2 covering layer; 3 mask layer & label layer; 4 optical glue; 5 first layer sensing unit and substrate; 6 optical glue; 7 second layer sensing unit and substrate; 8 air layer or optical glue The thickness of surface shield is usually less than 100um.
hard shield is required on all plastic covering layers.
this is because finger touch will scratch the plastic surface. If the covering layer is glass, surface shield is unnecessary, but the glass must be chemically strengthened or quenched, and the surface shield needs to be optically matched with the covering layer, In order to avoid excessive light loss.
the thickness of the cover layer can be 0-3 mm.
not all touch screens need a cover layer, the thinner the cover layer is, The higher the SNR, the better the sensitivity.
the common materials are polycarbonate, plexiglass and glass.
the third layer is mask layer and label layer.
its thickness is about 100 mm.
the mask layer is located under the cover.
it can hide the edge of wiring and LCD.
it is allowed to add label text or icon in the design.
however, the label must be replaced The fourth layer is optical adhesive with a thickness of about 25-200 mm.
the thinner the optical adhesive is, the better the signal-to-noise ratio is. The optical adhesive with high dielectric constant (ER) can have better sensing finger capacitance, and thus higher signal-to-noise ratio can be obtained.
PSA pressure sensitive adhesive is usually used.
PSA pressure sensitive adhesive is widely usedThe thickness of ITO coating is less than 100 nm. The substrate of ITO coating can be 100 um ~ 1 mm glass (IR ~ 1.52) or 25 mm ~ 300 mm PET film (IR ~ 1.65).
the thicker the ITO, the lower the resistance per unit area and the better the signal-to-noise ratio, The better the transmittance is.
the substrate can be thin film or glass.
If ITO is used as the lower surface of the glass substrate.
the glass substrate can be used as the surface cover.
the sixth layer is another layer of optical adhesive.
compared with the previous layer of optical adhesive, the thicker the layer of optical adhesive, the better the signal-to-noise ratio, This layer of optical adhesive is usually used in combination with ACA anisotropic conductive adhesive, and the seventh layer is also the sensing unit and substrate, which is the same material as the first substrate.
note that the film and glass should not be mixed.
If ITO is on the upper surface of the substrate.
thick substrate can obtain higher signal-to-noise ratio; if ITO is on the lower surface of the substrate, Thin substrate makes the signal-to-noise ratio higher.
it is also required to use heteroconductive adhesive in the edge region.
now there is a single substrate process to simplify the production and reduce the cost.
the eighth layer is air or optical adhesive layer.
we know that the dielectric constant of air is equal to 1, This can reduce the parasitic capacitance from the upper surface of LCD.
if optical glue is used,
it can make the installation more robust.
it is necessary to match the optical parameters to reduce the light loss.
it is necessary to select the optical glue with the lowest dielectric constant as far as possible, and ensure the minimum distance between the ITO sensing unit and the upper surface of LCD is 250mm.
finally, the LCD screen.
it is necessary to select the optical glue with the lowest dielectric constant as possibleFor the touch screen design, it is a noise source. The noise comes from the backlight and the LCD pixel driving control signal. Generally, the passive dot matrix screen is not used, which will generate high voltage signal on the front of the LCD. The active dot matrix screen with VCOM is used as far as possible, which can form a virtual ground or shielding function. If the passive dot matrix screen is really needed, an ITO shielding layer needs to be added to the touch screen, The shield must be grounded, To remove the influence of parasitic capacitance CP.
multi touch screen controller is the core of the touch screen module.
this paper introduces the touch screen controller of cypress as an example.
the touch screen controller of cypress is truetouch series.
it is based on the widely used PSoC (programmable system chip) technology.
PSoC integrates programmable simulation and control Digital peripheral and mixed signal array of MCU core.
so the flexibility, programmability, high integration and other characteristics of PSoC are also suitable for truetouch scheme.
truetouch scheme is an inductive capacitive touch screen scheme.
the structure of this touch screen has been introduced before.
it can be said that there are many manufacturers and types of LCD.
there are also many inductive devices, such as glass, thin film, ITO, etc, Even there are many models of ITO.
truetouch is based on PSoC technology.
so the flexibility of PSoC makes it work well with many LCDs and ITO.
why is the touch screen controller of cypress called truetouch scheme.
or how does this "true" come from? Looking back on the development of touch screen, from the beginning, single touch can only have one finger to touch or slide; later, multi touch gesture also came into being, which can recognize the direction of two fingers,But we can't judge their specific position, and we can zoom, pan, rotate and other operations. Today, true touch of cypress can achieve multi touch all point, which can recognize multiple fingers and determine the exact position. It's true multi touch, which is also the origin of true.
truetouch's product series can be divided into three categories.
single touch, Each type has different models.
there are differences in screen size, scanning speed, communication mode, memory size and power consumption, these devices are simple and powerful, so they can be used in different applications The value of truetouch solution is mainly reflected in the following aspects: maintaining the inherent beauty, lightness and thinness of touch screen.
it can make customers' products stand out; adopting inductive capacitance touch screen technology, without mechanical devices, it is more durable; having a complete series, from single touch to multi touch recognition, Then to the multi touch recognition position; based on PSoC technology, it is flexible to use, and can be used with many LCD and ITO; all the value of PSoC can be reflected in truetouch, such as flexibility, programmability, etc., which can shorten the development cycle, make the product come to market quickly, and has high integration, which can integrate many peripheral devices into PSoC (truetouch product),This can not only reduce the system cost, but also reduce the overall power consumption and improve the power efficiency.
conclusion this paper introduces the multi touch technology, touch screen and touch screen controller.
it can be said that.
touch screen is the final choice of man-machine interface.
whether it is single touch or multi touch recognition direction, or multi touch recognition position, They have obvious advantages in many applications, such as mobile phone, MP3, GPS and so on.
these products are required to have the characteristics of small size and portability.
how to make small volume products play more functions depends on the application of touch screen.
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