Capacitive touchscreen controller offers improved noise rejection

October 14, 2013 // By Graham Prophet
For use with designs such as large-screen superphones and tablets, Cypress’ TrueTouch Gen5 touchscreen controller, TMA568, supports precise passive stylus functions and palm-rejection while silencing noise from chargers and displays

Providing noise-immune touchscreen control technology to superphones, smartphones, tablets and e-readers, the TMA568 controller supports writing and drawing with a 2.0-mm-tip stylus, allowing touchscreens to capture characters as small as 7mm. The TMA568 also adds a palm rejection feature that recognises a user's palm and prevents any unintended touch inputs. In addition, the controller boosts responsiveness by integrating 58 sense I/Os and 21 parallel receive channels, enabling scanning of the entire panel in a single pass.

Noise from displays and after-market chargers can disrupt a touchscreen’s ability to operate properly. The TrueTouch Gen5 family’s ChargerArmor feature offers 40 Vpp charger noise immunity measured from 1 to 500 kHz with an ultra-thin 0.5-mm cover lens and a finger-size up to 22 mm—the most stringent specifications used to measure any touchscreen controller. Cypress asserts that no competing controllers deliver noise immunity over 15 Vpp under these conditions. The controller provides precise tracking of smaller fingers and styluses by allowing for tight spacing of touchscreen sensors, and it supports screens up to 8.3 inches at a 5.0-mm sensor pitch.

With Cypress’s DualSense technology to execute both self-capacitance and mutual-capacitance measurements in the same device, the Gen5 family offers high levels of waterproofing for operation in the the presence of rain, condensation, or sweat. By combining this architecture with an ARM Cortex M-Core processor, the TMA568 controller offers 120-Hz refresh rates, and averages low power consumption of 12 mW in active mode and 15 µW in deep-sleep mode. Gen5 controllers drive the touchscreen at 10V and at high frequency with narrow-band, single-pass scanning and advanced hardware DSP filtering.