Fingerprint detection circuit and electronic device
View Patent ↗A fingerprint detection circuit and an electronic device are provided. The fingerprint detection circuit is configured to apply an excitation signal to a finger so as to generate finger capacitors, and the fingerprint detection circuit includes: a signal amplifier having a negative input terminal connected with one of the finger capacitors, a positive input terminal connected with a ground terminal, and an output terminal to output an output voltage according to a capacitance value of the one of the finger capacitors; a capacitor connected between the negative terminal and the output terminal of the signal amplifier; a rheostat; and a switch unit connected with the rheostat in series and configured to control the rheostat to be connected with the capacitor in parallel, such that the output voltage has a non-linear relationship with the capacitance value of the one of the finger capacitors.
1. A fingerprint detection circuit, configured to apply an excitation signal to a finger so as to generate finger capacitors, the fingerprint detection circuit comprising:
a signal amplifier having a negative input terminal connected with one of the finger capacitors, a positive input terminal connected with a ground terminal, and an output terminal to output an output voltage according to a capacitance value of the one of the finger capacitors;
a capacitor connected between the negative terminal and the output terminal of the signal amplifier;
a rheostat;
a switch unit connected with the rheostat in series, and configured to control the rheostat to be connected with the capacitor in parallel, such that the output voltage has a non-linear relationship with the capacitance value of the one of the finger capacitors;
a sampling hold circuit connected to the output terminal of the signal amplifier; and
an analog-to-digital converter connected to a terminal of the sampling hold circuit.
2. The fingerprint detection circuit according to claim 1 , wherein the capacitance value of the one of the finger capacitors is determined according to a formula of
Vo =( Vs−Vt*Cx/Ci ),
in which, Vo is the output voltage, Vt is an excitation voltage of the excitation signal, Cx is the capacitance value of the one of the finger capacitors, Ci is a capacitance value of the capacitor, Vs is a voltage drop amplitude of the capacitor, Rs is a resistance value of the rheostat, and Ts is a detection time.
3. The fingerprint detection circuit according to claim 1 , wherein:
the switch unit comprises a first connecting terminal and a second connecting terminal;
the first connecting terminal is connected with a first terminal of the capacitor, the second connecting terminal is connected with a first terminal of the rheostat, and a second terminal of the rheostat is connected with a second terminal of the capacitor;
when the first connecting terminal is connected with the second connecting terminal, the rheostat is connected with the capacitor in parallel.
4. An electronic device, comprising a fingerprint detection circuit configured to apply an excitation signal to a finger so as to generate finger capacitors;
wherein the fingerprint detection circuit comprises:
a signal amplifier having a negative input terminal connected with one of the finger capacitors, a positive input terminal connected with a ground terminal, and an output terminal to output an output voltage according to a capacitance value of the one of the finger capacitors;
a capacitor, connected between the negative terminal and the output terminal of the signal amplifier;
a rheostat;
a switch unit connected with the rheostat in series, and configured to control the rheostat to be connected with the capacitor in parallel, such that the output voltage has a non-linear relationship with the capacitance value of the one of the finger capacitors;
a sampling hold circuit connected to the output terminal of the signal amplifier; and
an analog-to-digital converter connected to a terminal of the sampling hold circuit.
5. The electronic device according to claim 4 , wherein the capacitance value of the one of the finger capacitors is determined according to a formula of
Vo =( Vs−Vt*Cx/Ci ),
in which, Vo is the output voltage, Vt is an excitation voltage of the excitation signal, Cx is the capacitance value of the one of the finger capacitors, Ci is a capacitance value of the capacitor, Vs is a voltage drop amplitude of the capacitor, Rs is a resistance value of the rheostat, and Ts is a detection time.
6. The electronic device circuit according to claim 4 , wherein:
the switch unit comprises a first connecting terminal and a second connecting terminal;
the first connecting terminal is connected with a first terminal of the capacitor, the second connecting terminal is connected with a first terminal of the rheostat, and a second terminal of the rheostat is connected with a second terminal of the capacitor;
when the first connecting terminal is connected with the second connecting terminal, the rheostat is connected with the capacitor in parallel.
7. The electronic device circuit according to claim 4 , further comprising a fingerprint sensor connected with the fingerprint detection circuit, and configured to generate the finger capacitors with the finger.