Fingerprint Detection Circuit With Common-Mode Noise Isolation
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Solution Overview
Problem
Fingerprint detection systems face inaccuracies due to sensor power noise affecting photo-detected voltage, which impacts identification results.
Innovation Solution
A detection circuit is designed with a photo diode connected to a common-mode voltage and a sampling switch, using an integrator to generate a time-integral signal and an ADC for digital conversion, while coupling the common-mode voltage to prevent noise from affecting the photo-detected voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photo sensor is used to detect fingerprint patterns, then the fingerprint detection function is achieved, but sensor power noise affects the photo-detected voltage and degrades measurement precision
Solution Approach 1:
The patent introduces a common-mode voltage as an intermediary signal that is coupled to both the photo sensor and the integrator. This common-mode voltage serves as a reference that tracks and compensates for power noise, allowing the integrator to differentiate between actual fingerprint signals and noise-induced voltage fluctuations. The intermediary voltage effectively mediates the noise compensation process without requiring complex additional circuitry.
Solution Approach 2:
The patent implements a feedback mechanism where the common-mode voltage is continuously monitored and fed back to the integrator circuit. This feedback loop allows the system to dynamically adjust for power noise variations in real-time, ensuring that the photo-detected voltage remains accurate despite fluctuations in the power supply. The feedback ensures that noise compensation is ongoing and adaptive to changing conditions.
2Speed
If the detection circuit processes sense signals directly from the photo sensor, then the processing speed is maintained, but noise in the common-mode voltage affects the time-integral signal
Solution Approach 1:
The common-mode voltage acts as an intermediary reference signal that is coupled to the integrator, allowing it to distinguish between genuine signal variations and noise-induced fluctuations. This intermediary voltage provides a stable reference that enables the integrator to process signals quickly while simultaneously filtering out noise, thus maintaining both speed and precision.
Solution Approach 2:
The patent converts the harmful effect of common-mode voltage noise into a beneficial reference signal. By intentionally coupling the common-mode voltage to the integrator, the system uses the noise-containing voltage as a reference to identify and subtract noise components from the photo-detected signal. This transforms the harmful noise into a useful diagnostic reference that improves overall signal accuracy.
3Measurement precision
If noise compensation mechanisms are added to the detection circuit, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The common-mode voltage serves as a simple intermediary that provides noise compensation without requiring complex additional circuitry. Instead of implementing complicated noise filtering algorithms or multiple sensors, the patent uses a single common-mode voltage coupling that naturally provides the necessary noise reference. This approach achieves precision improvement with minimal added complexity.
Solution Approach 2:
The detection circuit performs self-service noise compensation by using its own common-mode voltage as the reference signal. The system does not require external noise references or additional calibration procedures; the common-mode voltage inherently contains the noise information needed for compensation. This self-service approach simplifies the overall system architecture while maintaining high measurement precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively mitigates the impact of sensor power noise on fingerprint detection, enhancing the accuracy of identification results by isolating noise from the photo-detected voltage.
Implementation Method 1
a photo diode having an anode electrode connected to a first common-mode voltage and a cathode electrode providing a photo-detected voltage
Implementation Method 2
an integrator coupled to receive the photo-detected voltage via the sampling switch and configured to generate time integral of the photo-detected voltage
Data Source
AI summary
A detection circuit adaptable to a fingerprint detection system includes 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; and an analog-to-digital converter (ADC) that converts the time-integral signal into a digital form. 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.