Automotive Electromagnetic Compatibility Standard Specific Pulse Driving Method for Advanced In-Cell Touch Sensor

In this work, a novel pulse driving method for advanced in-cell touch (AIT) panels is proposed to meet the automotive electromagnetic interference (EMI) requirements. AIT panels are usually driven by load-free driving (LFD) to overcome the large parasitic capacitances of the in-cell touch sensors. However, strong EMI is emitted from the AIT panels, by the harmonics of the driving pulses used for LFD. Thus, a novel driving pulse for LFD is necessary to resolve the EMI problems. The proposed driving pulse is created from the frequency-spread pulse chain with a duty cycle 0.46. The spread-spectrum effect is enhanced by alternating two types of pulse chains with different frequencies. Consequently, the EMI emissions of the fifth harmonic, which is the main factor associated with EMI reduction, is attenuated by 15 dB. The first and third harmonics are fitted to a frequency band without any CISPR-25 specification. Thus, the automotive EMI requirements can be satisfied. The touch performance remained unchanged. The existing circuit components, which are designed for pulse driving, can be employed without additional modification, unlike in the case of sine-wave driving. The proposed pulse chain can provide optimized pulse driving for AIT panels.