UCLA

In this thesis, an oscillator-based touch sensor detection circuit with adaptive resolution has been proposed. Current popular touch screen detection technologies include resistive, capacitance, infrared based imaging sensor; however, some are designed with a fixed resolution and it is not optimal for nowadays low power requirement.

In order to solve this problem, an oscillator-based touch sensor detection circuit with adaptive resolution has been presented. The circuit detects the touching finger by using a 6 stage ring oscillator to sense the change of the input capacitance. To make the resolution tunable, an 8 bit R-2R DAC has been implemented to change the bias voltage of the ring oscillator which will change the oscillator's resonant frequency as well as system resolution. Finally, a digital processing unit has been designed which is used to analyzes the change of the frequency and transfer information to PC to do post-signal processing

The design is achieved by using TSMC 65nm technology, occupying an area of 0.9mm x 1.1mm, power consumption of 10mW when oscillating at 120MHz, and runs on a digital clock frequency of 100KHz. Test result shows that the system can be very sensitive to detect if a finger touch it or not and the resolution can be adaptive by changing the frequency of the oscillator through DAC's output