Ultrasonic touch sensor with active feedback

A touch sensor, comprising:

• a housing having an ultrasound chamber;
• a touch structure coupled to the housing and arranged over the ultrasound chamber such that the ultrasound chamber forms an enclosed interior volume, wherein the touch structure comprises a touch interface;
• a transmitter arranged inside the enclosed interior volume, wherein the transmitter is configured to transmit an ultrasonic transmit wave towards the touch structure;
• a receiver arranged inside the enclosed interior volume and coupled to the transmitter via a propagation path, wherein the receiver is configured to receive an ultrasonic reflected wave produced from the ultrasonic transmit wave and the propagation path;
• a programmable voltage source configured to provide a bias voltage to the transmitter or to the receiver;
• a receiver circuit configured to convert the ultrasonic reflected wave into a measurement signal and generate an error value representative of a difference between a measured value of the measurement signal and a reference value;
• a controller configured to adjust the bias voltage to a voltage level that reduces the error value;
• and
• a measurement circuit configured to measure the adjusted bias voltage and determine whether a no-touch event or a touch event has occurred at the touch interface based on a comparison of the measured adjusted bias voltage and a bias voltage threshold.