Operating a fingerprint sensor comprised of ultrasonic transducers

A method for operating a fingerprint sensor comprising an array of ultrasonic transducers, the method comprising:

• activating a plurality of subsets of the ultrasonic transducers of the fingerprint sensor, wherein the plurality of subsets are non-adjacent;
• receiving a plurality of signals corresponding to the plurality of subsets of the ultrasonic transducers of the fingerprint sensor;
• determining whether a signal value for at least one received signal of the plurality of signals satisfies a signal threshold range from a signal mean, wherein the signal mean varies over time;
• and
• provided that the signal value for the at least one received signal of the plurality of signals does not satisfy the signal threshold range from the signal mean, determining an interaction between an object and the fingerprint sensor.

An ultrasonic fingerprint sensor device comprising:

• an array of ultrasonic transducers for emitting ultrasonic signals and capturing reflected ultrasonic signals from a finger interacting with the ultrasonic fingerprint sensor device;
• and a processor capable of controlling the ultrasonic fingerprint sensor device, wherein the processor is operable to:
• activate a plurality of subsets of the ultrasonic transducers or the fingerprint sensor, wherein the plurality of subsets of the ultrasonic transducers of the fingerprint sensor correspond to non-adjacent individual pixels;
• receiving a plurality of signals corresponding to the plurality of subsets of the ultrasonic transducers of the fingerprint sensor;
• determining whether a signal value for at least one received signal of the plurality of signals satisfies a signal threshold range from a signal mean, wherein the signal mean varies over time;
• provided that the signal value for the at least one received signal of the plurality of signals does not satisfy the signal threshold range from the signal mean, determining an interaction between an object and the fingerprint sensor;
• and
• update the signal mean based at least in part on the signal value.

A method for operating a fingerprint sensor comprising an array of ultrasonic transducers, the method comprising:

• operating the fingerprint sensor in a first phase of a finger detection mode, wherein the first phase activates a first subset of ultrasonic transducers to determine whether an object is interacting with the fingerprint sensor;
• responsive to the first phase determining that an object is interacting with the fingerprint sensor, operating the fingerprint sensor in a second phase of the finger detection mode, wherein the second phase activates a second subset of ultrasonic transducers to determine whether the object is indicative of a human finger based on a one-dimensional structure analysis of the object;
• and
• responsive to the second phase determining that the object is indicative of a human finger, operating the fingerprint sensor in a third phase of the finger detection mode, wherein the third phase activates a third subset of ultrasonic transducers to determine whether the object is a human finger based on a two-dimensional structure analysis of the object.