# US 10,482,306 B2 · Fingerprint sensing system and method

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- Number: US 10,482,306 B2
- Document ID: US10482306B2
- Status: Granted
- Kind: B2
- Application number: 15/642,272
- Filed: 2017-07-05
- Published: 2018-01-11
- Granted: 2019-11-19
- Earliest claimed: 2016-07-05
- Assignees: NXP B.V.
- Applicants: NXP B.V.
- Inventors: Thomas Suwald
- Web page: https://patentgrep.com/patent/US10482306B2

## CPC

- G06V 40/1306: {non-optical, e.g. ultrasonic or capacitive sensing}
- G06V 40/1365: {Matching; Classification}
- G06V: IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING

## Abstract

According to a first aspect of the present disclosure, a fingerprint sensing system is provided, comprising: a sensing unit configured to measure a physical property of a sensing cell and to produce a voltage in dependence on said physical property; and an analog-to-digital converter configured to convert said voltage into a digital signal, wherein said analog-to-digital converter implements a non-linear conversion function. According to a second aspect of the present disclosure, a corresponding fingerprint sensing method is conceived. According to a third aspect of the present disclosure, a corresponding computer program product is provided.

## Claims

### Claim 1

A fingerprint sensing system, comprising:
a capacitance-to-voltage converter configured to measure a capacitance from a fingerprint sensing cell and to produce a voltage in dependence on said capacitance from the fingerprint;
an analog-to-digital converter configured to convert said voltage into a digital signal, wherein said analog-to-digital converter implements a non-linear conversion function; and
a look-up table used to convert the digital signal to a value representing a measured valley depth of the fingerprint.

### Claim 2 (depends on 1)

The system of claim 1, wherein the analog-to-digital converter implements a logarithmic conversion function.

### Claim 3 (depends on 2)

The system of claim 2, wherein the logarithmic conversion function has a base of two.

### Claim 4 (depends on 2)

The system of claim 2, wherein the logarithmic conversion function has a base calculated in dependence on a signal-to-noise ratio of the capacitance-to-voltage converter.

### Claim 5 (depends on 4)

The system of claim 4, wherein the look-up table provides a de-logarithmization of the logarithmic conversion function.

### Claim 6 (depends on 5)

The system of claim 5, wherein the look-up table is configurable by a host processor.

### Claim 7 (depends on 4)

The system of claim 4, further comprising a transformation unit configured to perform a fast Fourier transformation on output values provided by the look-up table.

### Claim 8 (depends on 1)

The system of claim 1, wherein the valley depth represents the distance between a surface of the sensing cell and the surface of a finger.

### Claim 9 (depends on 1)

The system of claim 1, wherein the look-up is configured to provide values that are powers of 2.

### Claim 10 (depends on 1)

The system of claim 1, wherein the analog-to-digital converter is a logarithmic pipelined analog-to-digital converter.

### Claim 11 (depends on 1)

The system of claim 1, wherein the analog-to-digital converter is a flash analog-to-digital converter.

### Claim 12 (depends on 1)

The system of claim 1, wherein the analog-to-digital converter has a reciprocal conversion characteristic.

### Claim 13 (depends on 1)

A smart card comprising the fingerprint sensing system of claim 1.

### Claim 14

A fingerprint sensing method, comprising:
using a capacitance-to-voltage converter to measure a capacitance from the fingerprint sensing cell to produce a voltage in dependence on said physical property;
providing an analog-to-digital converter that implements a logarithmic conversion function to convert said voltage into a digital signal; and
using a look-up table to convert the digital signal to a value representing a linearization of the logarithmic conversion function to provide a measurement of a valley depth of the fingerprint.

### Claim 15 (depends on 14)

A non-transitory computer program product comprising instructions which, when executed by a processing unit, cause said processing unit to carry out or control the method of claim 14.

### Claim 16 (depends on 14)

The method of claim 14, wherein the logarithmic conversion function has a base of two.

### Claim 17 (depends on 14)

The method of claim 14, further comprising performing a fast Fourier transformation of the value provided by the look-up table.

### Claim 18 (depends on 14)

The method of claim 14, further comprising configuring the look-up table using a host processor.