Display device and fingerprint sensing circuit
The fingerprint sensing circuit includes a photo detector, a capacitor, a current mirror and a switch circuit. The capacitor has a first terminal electrically connected to the first terminal of the photo detector. The current mirror has an input terminal electrically connected to the first terminal of the photo detector and an output terminal electrically connected to a sensing line. In an exposure period, the switch circuit turns off the current mirror. In a sensing period, the switch circuit turns on the current mirror to generate a current on the sensing line, and the detecting circuit is configured to generate a fingerprint signal according to the current.
1. A display device comprising:
a detecting circuit; and
a display panel comprising a plurality of pixel units and a plurality of fingerprint sensing circuits, wherein each of the fingerprint sensing circuits corresponds to at least one of the pixel units, electrically connected to the detecting circuit through a sensing line, and comprises:
a photo detector having a first terminal and a second terminal;
a capacitor having a first terminal electrically connected to the first terminal of the photo detector;
a current mirror having an input terminal electrically connected to the first terminal of the photo detector and an output terminal electrically connected to the sensing line; and
a switch circuit configured to control the current mirror,
wherein in an exposure period, the switch circuit is configured to turn off the current mirror,
wherein in a sensing period, the switch circuit is configured to turn on the current mirror to generate a current on the sensing line, and the detecting circuit is configured to generate a fingerprint signal according to the current.
2. The display device of claim 1 , wherein the current mirror comprises:
a first transistor having a first terminal electrically connected to a control terminal of the first transistor and the input terminal of the current mirror; and
a second transistor having a first terminal electrically connected to the output terminal of the current mirror, wherein a control terminal of the second transistor is electrically connected to the control terminal of the first transistor, and a second terminal of the second transistor is electrically connected to a second terminal of the first transistor and a system voltage.
3. The display device of claim 2 , wherein the switch circuit comprises:
a first switch having a first terminal electrically connected to the input terminal of the current mirror and a second terminal electrically connected to the first terminal of the photo detector; and
a second switch having a first terminal electrically connected to the output terminal of the current mirror and a second terminal electrically connected to the sensing line.
4. The display device of claim 2 , wherein the switch circuit comprises a switch having a first terminal electrically connected to the system voltage and a second terminal electrically connected to the second terminal of the first transistor and the second terminal of the second transistor.
5. The display device of claim 2 , wherein the second terminal of the photo detector is electrically connected to a bias voltage, and a second terminal of the capacitor is electrically connected to the bias voltage.
6. The display device of claim 5 , wherein the bias voltage is lower than the system voltage minus a threshold voltage of the first transistor.
7. The display device of claim 1 , wherein the detecting circuit comprises:
an integrating circuit having an input terminal electrically connected to the sensing line; and
an analog-to-digital converter having an input terminal electrically connected to an output terminal of the integrating circuit.
8. The display device of claim 1 , wherein the display panel further comprises a plurality of color filters corresponding to the pixel units respectively, wherein the color filters do not cover the photo detector of each of the fingerprint sensing circuits.
9. The display device of claim 1 , wherein the photo detector is a photo diode.
10. A fingerprint sensing circuit disposed in a display panel and corresponding to at least one pixel unit of the display panel, wherein the display panel comprises a sensing line electrically connected to a detecting circuit, the fingerprint sensing circuit comprises:
a photo detector having a first terminal and a second terminal;
a capacitor having a first terminal electrically connected to the first terminal of the photo detector;
a current mirror having a input terminal electrically connected to the first terminal of the photo detector and an output terminal electrically connected to the sensing line; and
a switch circuit configured to control the current mirror,
wherein in an exposure period, the switch circuit is configured to turn off the current mirror,
wherein in a sensing period, the switch circuit is configured to turn on the current mirror to generate a current on the sensing line, and the detecting circuit is configured to generate a fingerprint signal according to the current.
11. The fingerprint sensing circuit of claim 10 , wherein the current mirror comprises:
a first transistor having a first terminal electrically connected to a control terminal of the first transistor and the input terminal of the current mirror; and
a second transistor having a first terminal electrically connected to the output terminal of the current mirror, wherein a control terminal of the second transistor is electrically connected to the control terminal of the first transistor, and a second terminal of the second transistor is electrically connected to a second terminal of the first transistor and a system voltage.
12. The fingerprint sensing circuit of claim 11 , wherein the switch circuit comprises:
a first switch having a first terminal electrically connected to the input terminal of the current mirror and a second terminal electrically connected to the first terminal of the photo detector; and
a second switch having a first terminal electrically connected to the output terminal of the current mirror and a second terminal electrically connected to the sensing line.
13. The fingerprint sensing circuit of claim 11 , wherein the switch circuit comprises a switch having a first terminal electrically connected to the system voltage and a second terminal electrically connected to the second terminal of the first transistor and the second terminal of the second transistor.
14. The fingerprint sensing circuit of claim 11 , wherein the second terminal of the photo detector is electrically connected to a bias voltage, and a second terminal of the capacitor is electrically connected to the bias voltage which is lower than the system voltage minus a threshold voltage of the first transistor.
15. The fingerprint sensing circuit of claim 11 , wherein the photo detector is a photo diode.