# US 2021/0173501 A1 · Tft-based fingerprint sensing system with corrected read-out > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0173501 A1 - Document ID: US20210173501A1 - Status: Published application - Kind: A1 - Application number: 16/983,788 - Filed: 2020-08-03 - Published: 2021-06-10 - Earliest claimed: 2019-12-06 - Assignees: Fingerprint Cards AB - Applicants: Fingerprint Cards AB - Inventors: Andreas LARSSON; Frank RIEDIJK - Web page: https://patentgrep.com/patent/US20210173501A1 ## CPC - G06F 21/32: using biometric data, e.g. fingerprints, iris scans or voiceprints - G06F 3/04166: {Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving (Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184)} - G06F 3/0418: {for error correction or compensation, e.g. based on parallax, calibration or alignment} - G06F 3/044: by capacitive means - G06V 40/13: Sensors therefor - G11C 11/419: Read-write [R-W] circuits - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - G06V: IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract A fingerprint sensing system comprising a plurality of conductive selection lines; a plurality of conductive read-out lines crossing the selection lines; selection circuitry controllable to provide a selection signal on at least one selected selection line in the plurality of selection lines; a plurality of pixel elements formed at intersections between the selection lines and the read-out lines; a reference signal source configured to provide a reference signal; and read-out circuitry coupled to each read-out line in the plurality of read-out lines and to the reference signal source, the read-out circuitry being configured to acquire a read-out signal via a read-out line connected to a selected pixel element, when the selected pixel element provides the sensing signal; acquire a reference signal from the reference signal source; form a corrected read-out signal for the selected pixel element based on the read-out signal and the reference signal; and provide corrected read-out signals. ## Claims ### Claim 1 A fingerprint sensing system for sensing a finger surface of a finger, comprising: a plurality of conductive selection lines arranged in parallel to each other; a plurality of conductive read-out lines arranged in parallel to each other and crossing the selection lines; selection circuitry coupled to each selection line in the plurality of selection lines, and controllable to provide a selection signal on at least one selected selection line in the plurality of selection lines; a plurality of pixel elements, each being formed at a respective intersection between a selection line in the plurality of selection lines and a read-out line in the plurality of read-out lines, each pixel element in the plurality of pixel elements comprising: a sensing element responsive to a property indicative of a distance between the sensing element and the finger surface to provide an output indicating a sensed value of the property; and a sensing signal providing element coupled to the sensing element, the selection line and the read-out line, the sensing signal providing element being configured to provide to the read-out line, in response to the selection signal being provided on the selection line, a sensing signal being dependent on the output provided by the sensing element; a reference signal source configured to provide a reference signal; and read-out circuitry coupled to each read-out line in the plurality of read-out lines and to the reference signal source, the read-out circuitry being configured to: acquire a read-out signal via a read-out line connected to a selected pixel element, when the selected pixel element provides the sensing signal; acquire the reference signal from the reference signal source; form a corrected read-out signal for the selected pixel element based on the read-out signal and the reference signal; and provide corrected read-out signals for each pixel element in the plurality of pixel elements, wherein the fingerprint sensing system comprises: a TFT module including at least the selection lines, the read-out lines, and the pixel elements; and an ASIC coupled to the TFT-module, the ASIC including at least a portion of the read-out circuitry. ### Claim 2 (depends on 1) The fingerprint sensing system according to claim 1, wherein the reference signal source is at least partly included in the ASIC. ### Claim 3 (depends on 1) The fingerprint sensing system according to claim 1, wherein the reference signal source is at least partly included in the TFT-module. ### Claim 4 (depends on 3) The fingerprint sensing system according to claim 3, wherein: the fingerprint sensing system further comprises a conductive reference line; the read-out circuitry is coupled to the reference signal source via the reference line; and the reference line is included in the TFT-module. ### Claim 5 (depends on 4) The fingerprint sensing system according to claim 4, wherein the reference line is arranged in parallel with the plurality of read-out lines. ### Claim 6 (depends on 1) The fingerprint sensing system according to claim 1, wherein the reference signal source includes at least one reference element included in the TFT-module. ### Claim 7 (depends on 6) The fingerprint sensing system according to claim 6, wherein: the sensing signal providing element comprised in each pixel element in the plurality of pixel elements includes semiconductor circuitry exhibiting a leakage current with a first temperature dependence, in the absence of the selection signal on the selection line coupled to the sensing signal providing element; and the at least one reference element includes semiconductor circuitry exhibiting a leakage current with a second temperature dependence. ### Claim 8 (depends on 7) The fingerprint sensing system according to claim 7, wherein the semiconductor circuitry comprised in the sensing signal providing element in each pixel element, and the semiconductor circuitry comprised in the at least one reference element are formed using the same materials and the same processing steps. ### Claim 9 (depends on 1) The fingerprint sensing system according to claim 1, wherein: the sensing element comprised in each pixel element in the plurality of pixel elements is responsive to an amount of light incident on the sensing element to provide an output indicating a sensed value of the amount of light; the at least one reference element comprises: a reference sensing element responsive to an amount of light incident on the reference sensing element to provide an output indicating a sensed value of the amount of light; and a reference signal providing element coupled to the reference sensing element and the read-out circuitry, the reference signal providing element being configured to provide to the read-out circuitry a reference sensing signal being dependent on the output provided by the reference sensing element; and the fingerprint sensing system further comprises an opaque shielding structure arranged to prevent light from reaching the reference sensing element of the at least one reference element. ### Claim 10 (depends on 1) The fingerprint sensing system according to claim 1, wherein: the sensing signal providing element comprised in each pixel element in the plurality of pixel elements is additionally coupled to a first driving voltage source; and the fingerprint sensing system comprises a plurality of reference elements, each reference element in the plurality of reference elements being coupled to a second driving voltage source and to the read-out circuitry. ### Claim 11 (depends on 10) The fingerprint sensing system according to claim 10, wherein: the sensing signal providing element comprised in each pixel element in the plurality of pixel elements includes a transistor with a source connected to the first driving voltage source, a drain connected to the read-out line, and a gate connected to the sensing element; and each reference element in the plurality of reference elements comprises a transistor with a source connected to the second driving voltage source, a drain connected to the reference line, and a gate connected to a reference potential. ### Claim 12 (depends on 1) The fingerprint sensing system according to claim 1, wherein: the fingerprint sensing system comprises a conductive reference line; the read-out circuitry is coupled to the reference signal source via the reference line; the sensing signal providing element comprised in each pixel element in the plurality of pixel elements is configured to provide the sensing signal in the form of a sensing current; and the read-out circuitry is configured to: receive a read-out current on the read-out line connected to the selected pixel element; receive a reference current on the reference line; and subtract the reference current from the read-out current, resulting in a corrected read-out current. ### Claim 13 (depends on 12) The fingerprint sensing system according to claim 12, wherein the read-out circuitry comprises integration circuitry configured to receive the corrected read-out current, and to convert the corrected read-out current received during an integration time to a read-out voltage. ### Claim 14 (depends on 13) The fingerprint sensing system according to claim 13, wherein the fingerprint sensing system further comprises correction circuitry connected to the reference line and configured to provide a time-varying potential to the reference line at an interface between the reference line and the read-out circuitry. ### Claim 15 (depends on 14) The fingerprint sensing system according to claim 14, wherein the correction circuitry is configured to provide the time-varying potential to the reference line as a potential that increases monotonically during the integration time. ### Claim 16 (depends on 1) An electronic device, comprising: the fingerprint sensing system according to claim 1; and processing circuitry coupled to the fingerprint sensing system, and configured to perform an authentication based on the corrected read-out signals provided by the read-out circuitry of the fingerprint sensing system.