Keep In “Touch” With EMI Solutions For Today’s Displays
Designers can take advantage of materials such as transparent conductor films, shielding tapes, and absorbers to enhance touch-sensor display performance.
Unpatterned transparent conductors (UTCs):To reduce the effect of internal-device-generated EMI noise on the PROCAP sensor, the use of second-generation UTCs (SG-UTCs) for EMI shielding is recommended. SG-UTC films are placed between the display and the PROCAP sensor, which is the common EMI noise source direction (Fig. 2). These films are transparent PET films with a conductive coating that’s been optimized not only for EMI shielding, but also for color, haze, and reflection characteristics. SG-UTCs are designed to offer excellent performance for PROCAP sensor designs.
PROCAP sensor E-field normalization and guard layer for PROCAP sensor optimization:Second-generation patterned transparent conductor (SG-PTC) films or SG-UTC films can offer “E-field normalization” of the PROCAP sensor by using either film in the display stack near the sensor. SG-PTC films can also be used in the PROCAP sensor to replace the ITO-based sensor design.
Looking at it more closely, the PROCAP sensor can have areas that are “electrically far or near” from other conducting surfaces (metal frame, bezel edges). Thus, the capacitance or inductance can vary across the PROCAP sensor. SG-UTC or SG-PTC can be used as an E-field normalization film or “guard” layer that modestly interacts with the PROCAP sensor array and unifies circuit performance across the sensor. It’s similar to metal layers that are used near flat flex cables to influence circuit impedance levels to optimize performance. Reduced variability of the PROCAP sensor due to environmental capacitance or inductance improves response and sensitivity. It also helps further simplify software and hardware integration.
SG-PTC films, which are patterned per a PROCAP sensor X-Y grid design, offer the potential for lower resistance traces along with excellent transparency versus comparable ITO sensor designs. SG-PTC sensor design could offer a lower RC time constant, enabling a faster sensor, particularly in display sizes of eight inches or more. The SG-PTC can also deliver improved flexibility and a narrower interconnect width versus a typical ITO-based touch sensor.
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