Autocalibration of acoustical stimulation signal for ultrasonic touch sensor

An ultrasonic touch sensor, comprising:

• a housing having an ultrasound chamber;
• a touch structure comprising a touch surface configured to receive a touch, wherein the touch structure is coupled to the housing and arranged over the ultrasound chamber;
• a signal generator configured to generate a sequence of excitation signals for producing a plurality of ultrasonic transmit waves, wherein the signal generator is configured to generate the sequence of excitation signals by varying a first signal parameter according to a plurality of first parameter values and varying a second signal parameter according to a plurality of second parameter values such that each excitation signal is different based on different combinations of a first parameter value of the plurality of first parameter values and a second parameter value of the plurality of second parameter values;
• a transmitter circuit arranged within the ultrasound chamber, wherein the transmitter circuit is configured to receive the sequence of excitation signals and sequentially transmit the plurality of ultrasonic transmit waves toward the touch structure based on the sequence of excitation signals, wherein each ultrasonic transmit wave corresponds to a respective excitation signal of the sequence of excitation signals;
• a receiver circuit arranged within the ultrasound chamber, wherein the receiver circuit is configured to receive a plurality of ultrasonic reflected waves, wherein each ultrasonic reflected wave is produced by a reflection of a respective ultrasonic transmit wave of the plurality of ultrasonic transmit waves, and wherein the receiver circuit is configured to generate a plurality of measurement signals representative of the plurality of ultrasonic reflected waves, wherein each measurement signal corresponds to a respective ultrasonic reflected wave of the plurality of ultrasonic reflected waves;
• and
• a measurement circuit coupled to the receiver circuit and configured to determine a cumulative signal energy for each measurement signal, determine which measurement signal out of the plurality of measurement signals has a highest cumulative signal energy, and configure, for a touch detection operation, the first signal parameter and the second signal parameter used by the signal generator with the first parameter value and the second parameter value that correspond to the measurement signal having the highest cumulative signal energy.

A method for calibrating an ultrasonic touch sensor, the method comprising:

• generating a sequence of excitation signals, including sweeping a signal parameter such that the signal parameter is set to a parameter value that is different for each excitation signal;
• sequentially transmitting a plurality of ultrasonic transmit waves based on the sequence of excitation signals, wherein each ultrasonic transmit wave corresponds to a respective excitation signal of the sequence of excitation signals;
• receiving a plurality of ultrasonic reflected waves, wherein each ultrasonic reflected wave is produced by a reflection of a respective ultrasonic transmit wave of the plurality of ultrasonic transmit waves;
• generating a plurality of measurement signals representative of the plurality of ultrasonic reflected waves, wherein each measurement signal corresponds to a respective ultrasonic reflected wave of the plurality of ultrasonic reflected waves;
• determining a cumulative signal energy for each measurement signal;
• determining which measurement signal out of the plurality of measurement signals has a highest cumulative signal energy;
• and
• configuring, for a touch detection operation, the signal parameter with the parameter value that corresponds to the measurement signal having the highest cumulative signal energy.