US 2001/0043728 A1Published application

Scanning capacitive semiconductor fingerprint detector

AssigneeSTMicroelectronics S.r.l.

InventorsAlan Kramer, James Brady

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Abstract

A scanning fingerprint detection system includes an array of capacitive sensing elements, the array having a first dimension greater than the width of a fingerprint and a second dimension less than the length of a fingerprint. Each of the capacitive sensing elements has first and second conductor plates connected across an inverting amplifier, the conductor plates forming capacitors with the ridges and valleys of a fingerprint of a finger pressed against a protective coating above the array, the inverting amplifier generating a signal indicative of a ridge or valley. Circuitry is provided for scanning the array to capture an image of a portion of fingerprint and for assembling the captured images into a fingerprint image.

Claims18

Dependent claims

A fingerprint detection system formed on a single semiconductor chip, the system comprising:

a rectangular scanning array defined by a first dimension and a second dimension wherein the first dimension is larger than the second dimension, the array comprising capacitive sensing cells arranged in rows and columns, the rows being aligned with the first dimension and the columns being aligned with the second dimension, the number of columns exceeding the number of rows;
a horizontal scanning stage connected to the array for scanning the rows of capacitive sensing cells;
a vertical scanning stage connected to the array for scanning the columns of capacitive sensing cells;
a scan control unit connected to the scanning stages for operating the scanning stages to enable one capacitive sensing cell at a time according to a predetermined scanning pattern to scan the entire array at a frame rate of multiple frames per second;
a thin protective layer disposed above the scanning array and providing a top surface for contact by a finger;
an A/D converter connected to each capacitive sensing cell and having an output;
and
output logic connected to the output of the A/D converter for capturing successive images at the frame rate as a finger is moved over the scanning array in a direction parallel to the second dimension while in contact with the top surface of the thin protective layer, and for assembling the successive images into a complete fingerprint image;
wherein each capacitive sensor cell comprises:
adjacent first and second thin conductor plates, the conductor plates being closely spaced relative to each other and lying beneath the top surface of the protective layer;
an inverting amplifier having an input and an output, the input being connected to the first conductor plate and the output being connected to the second conductor plate and to the A/D converter;
and a reference voltage source connected to the input of the inverting amplifier.

9 more elements

A fingerprint detection system formed on a single semiconductor chip, the system comprising:

a rectangular scanning array defined by a first dimension and a second dimension wherein the first dimension is larger than the second dimension, the array comprising capacitive sensing cells arranged in rows and columns, the rows being aligned with the first dimension and the columns being aligned with the second dimension, the number of columns exceeding the number of rows;
a horizontal scanning stage connected to the array for scanning the rows of capacitive sensing cells;
a vertical scanning stage connected to the array for scanning the columns of capacitive sensing cells;
a scan control unit connected to the scanning stages for operating the scanning stages to enable one capacitive sensing cell at a time according to a predetermined scanning pattern to scan the entire array at a frame rate of multiple frames per second;
a thin protective layer disposed above the scanning array and providing a top surface for contact by a finger;
an A/D converter connected to each capacitive sensing cell and having an output;
and
output logic connected to the output of the A/D converter for capturing successive images at the frame rate as a finger is moved over the scanning array in a direction parallel to the second dimension while in contact with the top surface of the thin protective layer, and for assembling the successive images into a complete fingerprint image;
wherein each capacitive sensor cell comprises:
adjacent first and second thin conductor plates, the conductor plates being closely spaced relative to each other and lying in a single plane proximate to and beneath the top surface of the protective layer;
an inverting amplifier having an input and an output, the input being connected to the first conductor plate and the output being connected to the second conductor plate and to the A/D converter;
and a reference voltage source connected to the input of the inverting amplifier.

9 more elements

A fingerprint detection system formed on a single semiconductor chip, the system comprising:

a rectangular scanning array defined by a first dimension and a second dimension wherein the first dimension is larger than the second dimension, the array comprising capacitive sensing cells arranged in rows and columns, the rows being aligned with the first dimension and the columns being aligned with the second dimension, the number of columns exceeding the number of rows;
a horizontal scanning stage connected to the array for scanning the rows of capacitive sensing cells;
a vertical scanning stage connected to the array for scanning the columns of capacitive sensing cells;
a scan control unit connected to the scanning stages for operating the scanning stages to enable one capacitive sensing cell at a time according to a predetermined scanning pattern to scan the entire array at a frame rate of at least 100 frames per second;
a thin protective layer disposed above the scanning array and providing a top surface for contact by a finger;
an A/D converter connected to each capacitive sensing cell and having an output;
and
output logic connected to the output of the A/D converter for capturing successive images at the frame rate as a finger is moved over the scanning array in a direction parallel to the second dimension while in contact with the top surface of the thin protective layer, and for assembling the successive images into a complete fingerprint image;
wherein each capacitive sensor cell comprises:
adjacent first and second thin conductor plates, the conductor plates being closely spaced relative to each other and lying in a single plane proximate to and beneath the top surface of the protective layer;
an inverting amplifier having an input and an output, the input being connected to the first conductor plate and the output being connected to the second conductor plate and to the A/D converter;
and a reference voltage source connected to the input of the inverting amplifier.

9 more elements

Dependencies are inferred from the claim text.