Finger Biometric Sensor Coupling Capacitor DC Offset Reset
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Fingerprint sensors using electric field sensing methods face challenges in capturing clear patterns when the finger is farther away due to weakened spatial field strength, leading to limitations in voltage usage causing discomfort or signal saturation, and DC offsets in amplifier stages that reduce the dynamic range of detected signals.
Innovation Solution
A finger biometric sensing device with an array of sensing pixel electrodes, series-coupled amplifiers, coupling capacitors, and reset circuitry to selectively reset amplifier inputs, increasing the dynamic range and reducing DC offsets while maintaining high sensitivity and low noise processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage is increased to compensate for weakened spatial field strength when finger is farther away, then fingerprint pattern strength increases, but sensor readout electronics may saturate, generate noise, or be damaged
Solution Approach 1:
The coupling capacitor is placed in advance between amplifier stages to block DC offsets before they can accumulate and saturate subsequent stages. This preliminary blocking action prevents the DC offset accumulation problem from occurring in the first place, allowing the amplifier chain to handle higher AC signal levels without saturation.
Solution Approach 2:
The coupling capacitor serves as an intermediary element between amplifier stages. It mediates the signal transmission by allowing AC components (fingerprint signal) to pass while blocking DC components (offsets). This intermediary function protects downstream electronics from DC offset accumulation while maintaining signal integrity.
2Power
If multiple amplifier stages are cascaded to amplify weak fingerprint signals, then signal amplification increases, but DC offsets accumulate from each stage limiting the dynamic range
Solution Approach 1:
The coupling capacitor extracts and removes the DC offset component from the signal path between amplifier stages. By taking out the harmful DC portion while retaining the useful AC fingerprint signal, the capacitor prevents offset accumulation and preserves the dynamic range of the amplifier chain.
3Ease of operation
If finger is placed farther from sensor array to improve user comfort, then contact pressure and discomfort are reduced, but spatial field strength variations become weaker
Solution Approach 1:
The coupling capacitor is configured in advance to provide DC offset blocking, which enables the system to handle larger voltage swings needed for distant finger placement. This preliminary configuration allows the amplifier chain to operate with higher gain without saturation, thereby maintaining sensitivity for weak signals from distant fingers.
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 enhances the accuracy and sensitivity of fingerprint sensing by compensating for DC offsets and voltage limitations, allowing for clearer pattern detection even with thicker dielectric layers and reducing noise and power consumption.
Implementation Method 1
at least one coupling capacitor between an output of a given amplifier and a corresponding input of a next amplifier
Implementation Method 2
Fingerprint sensors that are based upon electric field sensing methods measure the fingerprint pattern by establishing an electric field between the finger and the sensor array, and measuring the spatial fluctuations in field strength
Data Source
AI summary
A finger biometric sensing device may include an array of finger biometric sensing pixel electrodes and amplifiers coupled together in series and to be selectively coupled to respective ones of the array of finger biometric sensing pixels. The finger biometric sensing device may further include at least one coupling capacitor between an output of a given amplifier and a corresponding input of a next amplifier of the plurality thereof, and reset circuitry capable of selectively resetting the input of the next amplifier.