Fingerprint detection circuit, sensor and touch screen
A fingerprint detection circuit includes: a detection electrode, where a first capacitance is formed between a finger and the detection electrode, a second capacitance is formed between the finger and a virtual ground, and a parasitic capacitance is formed between the detection electrode and the virtual ground; an amplifier, where an inverting input end of the amplifier is connected to the detection electrode and a non-inverting input end of the amplifier is connected to an excitation signal; and a feedback capacitance, where one end of the feedback capacitance is connected to the inverting input end of the amplifier, the other end of the feedback capacitance is connected to an output end of the amplifier, and the output end of the amplifier outputs an output signal of the fingerprint detection circuit. There is no need to connect an excitation signal to a finger of a user through an external electrode.
1. A fingerprint detection circuit, comprising:
a detection electrode, wherein a first capacitance is formed between a finger and the detection electrode, a second capacitance is formed between the finger and a virtual ground, and a parasitic capacitance is formed between the detection electrode and the virtual ground wherein the virtual ground comprises and alternating-current ground;
an amplifier, wherein an inverting input end of the amplifier is connected to the detection electrode and a non-inverting input end of the amplifier is connected to an excitation signal; and
a feedback capacitance, wherein one end of the feedback capacitance is connected to the inverting input end of the amplifier, an other end of the feedback capacitance is connected to an output end of the amplifier, and the output end of the amplifier outputs an output signal of the fingerprint detection circuit; and
wherein the output signal is;
V
out
=
V
in
[
1
+
CP
1
CF
+
CS
·
CP
2
CF
(
CS
+
CP
2
)
]
wherein V out is the output signal of the fingerprint detection circuit, V in is the excitation signal, CP 1 is the parasitic capacitance, CF is the feedback capacitance, CS is the first capacitance, and CP 2 is the second capacitance.
2. The fingerprint detection circuit according to claim 1 , wherein the detection electrode comprises a metal electrode.
3. The fingerprint detection circuit according to claim 1 , wherein when a difference between CP 2 and CS is greater than a preset threshold, the output signal is:
V
out
=
V
in
[
1
+
CP
1
CF
+
CS
CF
]
.
4. The fingerprint detection circuit according to claim 1 , further comprising a reset switch operable to connect the inverting input end of the amplifier with the output end of the amplifier.
5. The fingerprint detection circuit according to claim 1 , wherein the detection electrode is in the shape of a rectangle, a square, or a circle.
6. A fingerprint detection sensor, wherein the fingerprint detection sensor comprises a plurality of pixel units, each of the pixel units corresponds to one fingerprint detection circuit, and the fingerprint detection circuit comprises:
a detection electrode, wherein a first capacitance is formed between a finger and the detection electrode, a second capacitance is formed between the finger and a virtual ground, and a parasitic capacitance is formed between the detection electrode and the virtual ground wherein the virtual ground comprises an alternating-current ground;
an amplifier, wherein an inverting input end of the amplifier is connected to the detection electrode and a non-inverting input end of the amplifier is connected to an excitation signal; and
a feedback capacitance, wherein one end of the feedback capacitance is connected to the inverting input end of the amplifier, an other end of the feedback capacitance is connected to an output end of the amplifier, and the output end of the amplifier outputs an output signal of the fingerprint detection circuit; and
wherein the output signal is
V
out
=
V
in
[
1
+
CP
1
CF
+
CS
·
CP
2
CF
(
CS
+
CP
2
)
]
wherein V out is the output signal of the fingerprint detection circuit, V in is the excitation signal, CP 1 is the parasitic capacitance, CF is the feedback capacitance, CS is the first capacitance, and CP 2 is the second capacitance.
7. The fingerprint detection sensor according to claim 6 , wherein the plurality of pixel units are arranged in a two-dimensional array.
8. The fingerprint detection sensor according to claim 7 , wherein rows and columns of the two-dimensional array are perpendicular to each other.
9. A touch screen, comprising a fingerprint detection sensor according to claim 6 .
10. The touch screen according to claim 9 , wherein the plurality of pixel units are arranged in a two-dimensional array.
11. The touch screen according to claim 10 , wherein rows and columns of the two-dimensional array are perpendicular to each other.
12. The fingerprint detection sensor according to claim 6 , wherein the detection electrode comprises a metal electrode.
13. The fingerprint detection sensor according to claim 6 , wherein when a difference between CP 2 and CS is greater than a preset threshold, the output signal is:
V
out
=
V
in
[
1
+
CP
1
CF
+
CS
CF
]
.
14. The fingerprint detection sensor according to claim 6 , further comprising a reset switch operable to connect the inverting input end of the amplifier with the output end of the amplifier.
15. The fingerprint detection sensor according to claim 6 , wherein the detection electrode is in the shape of a rectangle, a square, or a circle.