Mutual Capacitive Sensing Touch Screen Controller for Ultrathin Display with Extended Signal Passband Using Negative...

Area of Science:

• Electrical Engineering
• Materials Science
• Human-Computer Interaction

Background:

• Flexible and thin displays in smart devices suffer from large coupling capacitance in touch screen panels (TSPs).
• This capacitance limits the signal passband to below 100 kHz, significantly reducing received signal integrity.
• High driving frequencies (hundreds of kHz) are used for noise avoidance, further challenging signal quality.

Purpose of the Study:

• To mitigate the signal degradation caused by large coupling capacitance in TSPs.
• To enhance the signal-to-noise ratio (SNR) for touch input detection in flexible displays.
• To enable more robust and accurate touch sensing in modern smart devices.

Main Methods:

• Implemented a negative capacitance circuit in parallel with the TSP coupling capacitance to reduce effective capacitance.
• Utilized an in-phase and quadrature demodulation scheme to compensate for phase fluctuations between signal and clock.
• Fabricated a test chip using a 0.35 µm complementary metal-oxide-semiconductor (CMOS) process.

Main Results:

• Successfully reduced the effective capacitance at the analog front-end.
• Achieved a signal-to-noise ratio (SNR) of 43.2 dB for a 6 mm diameter metal pillar touch input.
• Demonstrated the efficacy of the negative capacitance and demodulation techniques.

Conclusions:

• The proposed negative capacitance circuit effectively overcomes the limitations of large coupling capacitance in flexible TSPs.
• The combination of negative capacitance and advanced demodulation techniques significantly improves touch input signal quality.
• This approach offers a viable solution for enhancing the performance of touch sensing in flexible electronic displays.