Half-bridge Fingeprint Sensing Method
AssigneeCypress Semiconductor Corporation
InventorsIgor Kravets, Roman Ogirko, Hans Klein, Oleksandr Hoshtanar
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Abstract
Fingerprint detection circuits with common mode noise rejection are described. The Fingerprint detection circuit includes a half-bridge circuit coupled to a receive (RX) electrode of an array of fingerprint detection electrodes and to a buried capacitance that is unalterable by the presence of a conductive object on the array. The fingerprint detection circuit may also include a listener electrode configured to enable common mode noise rejection through a differential input stage of a low noise amplifier (LNA).
Claims21
1-20. (canceled)
An array of fingerprint detection electrodes comprising:
- a first plurality of electrodes disposed along a first axis;
- and
- a second plurality of electrodes disposed along a second axis, wherein at least one of the second plurality of electrodes is split such that a first portion of the at least one of the second plurality of electrodes and a second portion of the at least one of the second plurality of electrodes are galvanically isolated.
A capacitance measurement system comprising:
- an array of fingerprint detection electrodes comprising:
- a first plurality of electrodes disposed along a first axis;
- and
- a second plurality of electrodes disposed along a second axis, wherein at least one of the second plurality of electrodes is split such that a first portion of the at least one of the second plurality of electrodes and a second portion of the at least one of the second plurality of electrodes are galvanically isolated.
- a capacitance measurement circuit coupled to each of the first plurality of electrodes and the second plurality of electrodes, the capacitance measurement circuit comprising a differential amplifier coupled to at least on of the first plurality of electrodes and the at least one of the second plurality of electrodes at a first input and a listener electrode for receiving common mode noise at a second input.
A method comprising:
- coupling a first electrode of a first plurality of electrodes to a transmit signal;
- coupling a second electrode the a second plurality of electrodes to a first input of a differential amplifier, the second electrode for receiving a receive signal derived from the transmit signal and a mutual capacitance between the first electrode and the second electrode, wherein at least one of the second plurality of electrodes is split such that a first portion of the at least one of the second plurality of electrodes and a second portion of the at least one of the second plurality of electrodes are galvanically isolated;
- coupling a listener electrode to a second input of the differential amplifier for receiving common mode noise;
- and
- converting the receive signal to digital value after removing the common mode noise received by the listener electrode.
Dependencies are inferred from the claim text.