In-glass fingerprint sensor and sensing circuit thereof
A sensor device includes a biometric sensor, which includes a substrate and a plurality of sensing electrodes over the substrate. The sensor device also includes an amplifier electrically coupled to the biometric sensor and configured to provide an output signal in response to a touch event received by the biometric sensor. The sensor device further includes an interface circuit arranged between the amplifier and the plurality of sensing electrodes.
1. A sensor device, comprising:
a biometric sensor comprising:
a substrate; and
a plurality of sensing electrodes over the substrate;
an amplifier electrically coupled to the biometric sensor and configured to provide an output signal in response to a touch event received by the biometric sensor; and
an interface circuit including a resistor and arranged between the amplifier and the plurality of sensing electrodes,
wherein the amplifier comprises a first stage coupled to a second stage through a coupling capacitor, the second stage defining a transconductance, wherein the resistor has a resistance greater than about ten times an inverse of the transconductance.
2. The sensor device of claim 1 , wherein the biometric sensor is a touch-mode biometric sensor.
3. The sensor device of claim 1 , wherein the biometric sensor includes a substrate formed of glass, quartz, or silicon oxide.
4. The sensor device of claim 1 , further comprising a display disposed below the biometric sensor, wherein the substrate is transparent to light emitted by the display.
5. The sensor device of claim 1 , wherein the amplifier comprises a non-inverting terminal and an inverting terminal, wherein the resistor is connected to the inverting terminal in series.
6. A sensor device, comprising:
a biometric sensor comprising:
a substrate; and
a plurality of sensing electrodes over the substrate;
an amplifier electrically coupled to the biometric sensor and configured to provide an output signal in response to a touch event received by the biometric sensor; and
an interface circuit arranged between the amplifier and the plurality of sensing electrodes, wherein the interface circuit comprises:
a current source connected between the biometric sensor and ground;
an amplify capacitor coupled between the current source and the amplifier; and
a first switch coupled between the current source and the amplify capacitor.
7. The sensor device of claim 6 , further comprising a voltage buffer between at least one of the plurality of sensing electrodes and the current source.
8. The sensor device of claim 6 , wherein the first switch of the interface circuit is closed during a first sampling phase of a sensing operation.
9. The sensor device of claim 6 , wherein the interface circuit further comprises a second switch, wherein the second switch comprises a first end connected to a node between the first switch and the amplify capacitor.
10. The sensor device of claim 9 , wherein the first switch is open while the second switch is closed during a second sampling phase of a sensing operation.
11. A sensor device, comprising:
a biometric sensor comprising:
a substrate; and
a plurality of sensing electrodes over the substrate;
an amplifier electrically coupled to the biometric sensor and configured to provide an output signal in response to a touch event received by the biometric sensor;
an interface circuit including a resistor and arranged between the amplifier and the plurality of sensing electrodes;
a sensing control block configured to generate an initial sensing signal; and
a signal transmission element electrically coupled to the sensing control block and configured to transmit a transmit sensing signal to a user based on the initial sensing signal in response to the touch event.
12. The sensor device of claim 11 , wherein the signal transmission element comprises a frame disposed over the biometric sensor and configured to be in contact with the user during the touch event.
13. The sensor device of claim 11 , wherein the initial sensing signal having a plurality of sensing periods, wherein each of the sensing periods include a first sampling period alternatingly arranged with a second sampling period, in which the initial sensing signal has a waveform including a rising edge and a falling edge corresponding to start time instants of the first sampling period and the second sampling period, respectively.
14. The sensor device of claim 13 , wherein the sensing control block is configured to generate a first sensed signal and a second sensed signal consecutively during the first sampling period and the second sampling period, respectively, for a same site of the user.
15. The sensor device of claim 14 , further comprising a processor configured to generate a processed signal by subtracting the first sensed signal by the second sensed signal.
16. The sensor device of claim 1 , further comprising an analog-to-digital converter configured to convert the output signal to a digital signal.