Half-bridge fingeprint sensing method
AssigneeCypress Semiconductor Corporation
InventorsIgor Kravets, Roman Ogirko, Hans Klein, Oleksandr Hoshtanar
Life of this patent
Estimating the term…
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).
Claims12
A differential capacitance measurement circuit comprising:
- a half-bridge circuit comprising a first mutual capacitor and a second mutual capacitor coupled to a first input of an amplifier;
- a listener electrode coupled to a second input of the amplifier;
- and
- a compensation circuit comprising:
- a modulator;
- a buffer coupled to an output of the modulator, the buffer configured to output a compensation signal;
- and
- a compensation capacitor coupled between an output of the buffer and the first input of the amplifier.
A method for measuring a capacitance comprising:
- receiving a first signal derived from the capacitance on a receive node, the receive node coupled to a first input of an amplifier;
- receiving a second signal derived from a buried capacitance on the receive node;
- receiving a third signal on a listener electrode, the listener electrode coupled to a second input of the amplifier;
- generating a differential output of the amplifier;
- converting the differential output of the amplifier to a digital value representative of the capacitance;
- and
- receiving a fourth signal on the receive node, wherein the fourth signal is configured to provide a compensation current to the input of the amplifier, and wherein the fourth signal is produced by a modulator coupled to a buffer, which is coupled to a compensation capacitor coupled to the first input of the amplifier.
Dependencies are inferred from the claim text.