Fingerprint Sensor Offset Cancellation via Signal Adjustment
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Solution Overview
Problem
Conventional fingerprint detection apparatuses face issues with inconsistent offset voltages across sensor pads, leading to deteriorated fingerprint image quality due to varying operation states and sensor pad designs, making it difficult to distinguish valley and ridge patterns.
Innovation Solution
An apparatus with a sensing signal adjusting unit that includes a data sample and hold unit, an offset sample and hold unit, and a programmable gain amplifier (PGA) to detect and adjust the offset voltage, ensuring a constant average voltage level across sensor pads, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If offset voltages are not adjusted across sensor pads, then the device structure remains simple, but the fingerprint image quality deteriorates due to varying offset voltages making it difficult to distinguish valley and ridge patterns
Solution Approach 1:
The patent applies preliminary action by detecting and storing offset voltages before actual fingerprint sensing occurs. The offset sample and hold unit captures the offset voltage from each sensor pad in advance, allowing the system to compensate for these variations during subsequent fingerprint detection without adding complexity to the main sensing operation.
Solution Approach 2:
The patent introduces intermediary components (offset sample and hold unit, PGA) that mediate between the sensor pads and the fingerprint processing system. These intermediaries measure and adjust offset voltages, enabling the main system to operate with consistent signal levels without requiring fundamental redesign of the sensor array.
2Measurement precision
If offset voltages vary across sensor pads, then the device can be manufactured simply, but the voltage values acquired vary making it difficult to distinguish valley and ridge patterns
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the voltage level parameter for each sensor pad based on its specific offset characteristics. The PGA modifies the gain and offset parameters of each sensor pad's output signal, transforming inconsistent voltage levels into a unified range that enables reliable fingerprint pattern recognition.
3Manufacturing precision
If no offset adjustment is performed, then the processing speed remains fast, but the fingerprint image quality becomes inconsistent across different sensor pads
Solution Approach 1:
The offset detection and storage operation is performed once before fingerprint sensing, rather than during each sensing operation. This preliminary calibration minimizes the time penalty, as subsequent fingerprint detections can directly use the stored offset values without repeated measurements.
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
The solution ensures a consistent fingerprint image quality, enhancing the accuracy of fingerprint authentication by effectively canceling offset voltages and amplifying signal differences between valley and ridge patterns without noise interference.
Implementation Method 1
an apparatus for detecting a fingerprint, which belongs to the capacitance method, acquires the shape of fingerprint (a fingerprint pattern) by detecting a change in capacitance according to valley and ridge shapes of fingerprint when the surface of the person's finger contacts a conductive sensing pattern
Data Source
AI summary
According to an embodiment of the present invention, an apparatus for detecting a fingerprint is provided, which includes a plurality of sensor pads receiving a response signal from a finger applied to a driving signal, a sensing circuit outputting a sensing signal based on the response signal, and a sensing signal adjusting unit sampling the sensing signal outputted from the sensing circuit maintaining the sensing signal, and adjusting an average voltage level of the sensing signal based on a reference voltage.