Hoonbae Kim’s research while affiliated with Yonsei University and other places

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.

For the first time, we analyze the mechanism of electromagnetic interference(EMI) in an advanced in-cell touch panel(AIT), which is a state-of-the-art in-cell touch screen panel(TSP) technology. The AIT panel has stronger EMI generation at a specific frequency band(0.15 MHz ~ 30 MHz) due to load free driving(LFD) method. LFD is adopted to overcome the structural vulnerability of in-cell touch panel, which incurs large parasitic capacitance due to the touch electrodes within the display panel. In order to overcome EMI problem, we present a novel driving method using pseudo random pulse(PRP). The power spectrum of PRP is well spread over the frequency band, resulting in a lower EMI. We measured EMI level with a near field probe and the proposed driving method shows EMI reduction of 6.5 dB. This EMI reduction is accomplished without structural reconfiguration, as well as the touch performance remains the same as that before PRP is applied. Therefore,the proposed driving method can be utilized in the field of automotive, military, and aviation industries as user interface which requires high touch performance and low EMI generation due to the peculiarities.