Fingerprint detection system and a detection circuit adaptable thereto

A fingerprint detection system, comprising:

• a sensor panel including:
• a photo diode having an anode electrode connected to a first common-mode voltage and a cathode electrode providing a photo-detected voltage;
• and
• a sampling switch coupled to receive the photo-detected voltage;
• a detection circuit including:
• an integrator coupled to receive the photo-detected voltage via the sampling switch and configured to generate time integral of the photo-detected voltage, thereby resulting in a time-integral signal;
• and
• an analog-to-digital converter (ADC) that converts the time-integral signal into a digital form;
• wherein the first common-mode voltage is coupled to the integrator to prevent noise occurred in the first common-mode voltage from affecting the time-integral signal;
• wherein the integrator comprises:
• an integrating amplifier;
• and
• an integrating capacitor connected between an output node and an inverting input node of the integrating amplifier;
• wherein the detection circuit comprises:
• a conversion switch connected between the integrator and the ADC;
• and
• a conversion capacitor connected between an input node of the ADC and ground;
• wherein the detection circuit comprises:
• a first buffer amplifier;
• a second buffer amplifier that provides a first reference voltage;
• and
• a first voltage adder that adds the first common-mode voltage and the first reference voltage, thereby resulting a sum voltage fed to a non-inverting input node of the first buffer amplifier, which provides the first reference voltage to a non-inverting input node of the integrating amplifier.

A detection circuit adaptable to a fingerprint detection system, the detection circuit comprising:

• an integrating amplifier coupled to receive a photo-detected voltage from a sensor panel and configured to generate time integral of the photo-detected voltage, thereby resulting in a time-integral signal;
• an analog-to-digital converter (ADC) that converts the time-integral signal into a digital form;
• a conversion switch connected between the integrating amplifier and the ADC;
• a conversion capacitor connected between an input node of the ADC and ground;
• a first buffer amplifier;
• a second buffer amplifier that provides a first reference voltage;
• and
• a first voltage adder that adds the first common-mode voltage and the first reference voltage, thereby resulting a sum voltage fed to a non-inverting input node of the first buffer amplifier, which provides the first reference voltage to a non-inverting input node of the integrating amplifier;
• wherein a first common-mode voltage of the sensor panel is coupled to the integrating amplifier to prevent noise occurred in the first common-mode voltage from affecting the time-integral signal.

A detection circuit adaptable to a fingerprint detection system, the detection circuit comprising:

• an integrating amplifier coupled to receive a photo-detected voltage from a sensor panel and configured to generate time integral of the photo-detected voltage, thereby resulting in a time-integral signal;
• an analog-to-digital converter (ADC) that converts the time-integral signal into a digital form;
• a first coupling capacitor with a first plate connected to receive the first common-mode voltage and a second plate electrically coupled to a non-inverting input node of the integrating amplifier;
• wherein a first common-mode voltage of the sensor panel is coupled to the integrating amplifier to prevent noise occurred in the first common-mode voltage from affecting the time-integral signal;
• a buffer amplifier that provides a reset voltage;
• a detection switch;
• and
• a second coupling capacitor with a first plate connected to receive the first common-mode voltage and a second plate electrically coupled to a non-inverting input node of the buffer amplifier via the detection switch.