Self-capacitive fingerprint sensor with active amplified pixels
In one aspect, a fingerprint sensor device includes a substrate and a sensor chip disposed over the substrate. The sensor chip includes an array of sensor pixels configured to generate fingerprint data by sensing ridges and valleys of a surface of a finger contacting the fingerprint sensor device. Each sensor pixel includes a single sensor electrode an amplifier having an inverting terminal electrically connected to the sensor electrode and a non-inverting terminal electrically connected to a drive signal. The drive signal generates electric fields between the sensor electrode and at least one of the ridges and valleys of the surface of the finger contacting the fingerprint sensor device to generate a variable capacitor having a variable capacitance based at least partly on a distance between the sensor electrode and the at least one of the ridges and valleys of the finger.
1. A fingerprint sensor device, comprising:
a substrate;
a fingerprint sensor disposed over the substrate, wherein the fingerprint sensor includes an array of sensor pixels configured to generate fingerprint data by sensing ridges and valleys of a surface of a finger contacting the fingerprint sensor device; and
a pressure sensor disposed over the substrate at a plane of the fingerprint sensor, wherein the pressure sensor is configured to detect a pressure from the finger to communicate an unlock signal to initiate fingerprint detection;
wherein the fingerprint sensor is configured to send the unlock signal, responsive to the detected touch from the finger, to a main processor to indicate a request to initiate fingerprint detection; receive a response signal, responsive to the send unlock signal, from the main processor acknowledging that a mobile device is waking up; and initiate a fingerprint detection responsive to the received response signal.
2. The fingerprint sensor device of claim 1 , further comprising a lateral vibrator to provide a haptic feedback to the finger.
3. The fingerprint sensor device of claim 1 , wherein the fingerprint sensor and the pressure sensor are integrated into a single integrated circuit chip.
4. The fingerprint sensor device of claim 1 , wherein the fingerprint sensor and the pressure sensor are integrated into a system on a chip.
5. The fingerprint sensor device of claim 1 , wherein each sensor pixel includes:
a single sensor electrode; and
an amplifier having an inverting terminal electrically connected to the sensor electrode and a non-inverting terminal electrically connected to a drive signal;
wherein the drive signal generates electric fields between the sensor electrode and at least one of the ridges and valleys of the surface of the finger contacting the fingerprint sensor device to generate a variable capacitor having a variable capacitance based at least partly on a distance between the sensor electrode and the at least one of the ridges and valleys of the finger;
wherein the amplifier is electrically connected to a feedback capacitor in a negative feedback loop between an output terminal and the inverting terminal of the amplifier.
6. The fingerprint sensor device of claim 1 , wherein:
the fingerprint sensor includes the array of sensor pixels electrically arranged in rows or columns.
7. The fingerprint sensor device of claim 6 , wherein:
the fingerprint sensor includes a signal processing unit electrically connected to the array of sensor pixels electrically arranged in rows or columns to process fingerprint data received from the array of sensor pixels.
8. The fingerprint sensor device of claim 7 , wherein:
the fingerprint sensor includes a multiplexing switch network configured to electrically connect the signal processing unit to the array of sensor pixels electrically arranged in rows or columns;
wherein the multiplexing switch network is configured to selectively electrically connect the signal processing unit to the array of sensor pixels one row or column at a time, to selectively power one or more sensor pixels in the corresponding row or column electrically connected to the signal processing unit.
9. An electronic device, comprising
a main processor; and
a fingerprint sensor device, including:
a substrate;
a fingerprint sensor disposed over the substrate, wherein the fingerprint sensor includes an array of sensor pixels configured to generate fingerprint data by sensing ridges and valleys of a surface of a finger contacting the fingerprint sensor device; and
a pressure sensor disposed over the substrate at a plane of the fingerprint sensor, wherein the pressure sensor is configured to detect a pressure from the finger to communicate an unlock signal to the main processor to unlock the electronic device and initiate fingerprint detection;
wherein the fingerprint sensor is configured to send the unlock signal, responsive to the detected touch from the finger, to the main processor to indicate a request to initiate fingerprint detection; receive a response signal, responsive to the send unlock signal, from the main processor acknowledging that a mobile device is waking up; and initiate a fingerprint detection responsive to the received response signal.
10. The electronic device of claim 9 , further comprising a lateral vibrator to provide a haptic feedback to the finger.
11. The electronic device of claim 9 , wherein the fingerprint sensor and the pressure sensors are integrated into a single integrated circuit chip.
12. The electronic device of claim 9 , wherein the fingerprint sensor and the pressure sensors are integrated into a system on a chip.
13. The electronic device of claim 9 , wherein each sensor pixel includes:
a single sensor electrode; and
an amplifier having an inverting terminal electrically connected to the sensor electrode and a non-inverting terminal electrically connected to a drive signal; wherein the drive signal generates electric fields between the sensor electrode and at least one of the ridges and valleys of the surface of the finger contacting the fingerprint sensor device to generate a variable capacitor having a variable capacitance based at least partly on a distance between the sensor electrode and the at least one of the ridges and valleys of the finger; and
a protective cover disposed over the fingerprint sensor device.
14. The electronic device of claim 13 , wherein the amplifier is configured to generate the output signal based at least on the variable capacitance and feedback capacitance of the feedback capacitor with no additional non-parasitic capacitances.
15. The electronic device of claim 13 , wherein the fingerprint sensor device disposed under the protective cover is configured to function as a virtual button with no mechanical actuators.
16. The electronic device of claim 9 , wherein:
the protective cover includes an opening, and the fingerprint sensor device is disposed through the opening; and
the fingerprint sensor device includes an integrated protective cover separate from the protective cover of the electronic device to protect the sensor chip against direct contact with the surface of the finger.
17. A method of unlocking a mobile device, the method comprising:
detecting, by a fingerprint sensor device in the mobile device, a touch from a finger;
sending a wakeup signal, responsive to the detected touch from the finger, to a main processor of the mobile device to initiate wakeup of the mobile device;
receiving a response signal, responsive to the send wakeup signal, from the main processor acknowledging that the mobile device is waking up; and
initiating a fingerprint detection responsive to the received response signal.
18. The method of claim 17 , wherein the detecting the touch comprises:
determining whether the detected touch is sustained for a predetermined period of time.
19. The method of claim 17 , wherein the detecting the touch comprises:
detecting a pressure from the finger; and
determining whether the detected pressure satisfies a predetermined amount.
20. The method of claim 17 , further comprising:
providing a haptic feedback to the finger to acknowledge that the touch has been detected.