Ultrasonic fingerprint sensor with passive and active common mode cancellation

An apparatus comprising:

• a piezoelectric layer configured to obtain an acoustic signal comprising a common mode component and a detection signal component indicative of a fingerprint pattern;
• a pixel array coupled at a first end of an electrical network and configured to receive the acoustic signal, wherein each pixel within the pixel array is coupled with at least a portion of the piezoelectric layer and is configured to detect at least a portion of the detection signal component;
• and
• a common mode canceling capacitive element coupled with the electrical network in parallel with the pixel array and configured to attenuate at least a portion of the common mode component from the acoustic signal before the acoustic signal is received by the pixel array.

An apparatus comprising:

• a piezoelectric layer configured to obtain an acoustic signal comprising a common mode component and a detection signal component indicative of a fingerprint pattern;
• a pixel array coupled at a first end of an electrical network and configured to receive the acoustic signal, wherein each pixel within the pixel array is coupled with at least a portion of the piezoelectric layer and is configured to detect at least a portion of the detection signal component;
• and
• common mode canceling circuitry coupled at a second end of the electrical network opposite the pixel array and configured to introduce a feedback signal through the electrical network to attenuate at least a portion of the common mode component at the pixel array.