Fingerprint Sensor Clock Synchronization for Ripple Noise Reduction
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Solution Overview
Problem
Fingerprint identification systems face reduced accuracy due to noise caused by ripple in the supply voltage generated by the charge pump circuit, which is not effectively addressed by existing technologies.
Innovation Solution
Synchronizing the first clock signal for the charge pump circuit with the second clock signal for the pixel circuit, ensuring the sampling interval is an integer multiple of the first clock signal's period, thereby maintaining a consistent average supply voltage and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the charge pump circuit generates supply voltage for the pixel circuit, then the pixel circuit can operate and convert touch capacitance to output signals, but the supply voltage contains ripple that introduces noise and reduces fingerprint identification accuracy
Solution Approach 1:
The patent applies periodic action by synchronizing the charge pump clock signal with the pixel clock signal, ensuring that the charge pump operates in a periodic manner that aligns with the sampling intervals of the pixel circuit. This synchronization causes the ripple in the supply voltage to occur at regular intervals that coincide with sampling boundaries, allowing the averaging process to effectively cancel out the ripple noise. The periodic alignment ensures that positive and negative ripple deviations average to zero over each sampling interval, thereby maintaining measurement precision while providing necessary power.
2Adaptability or versatility
If the pixel clock signal and charge pump clock signal are independent, then the system has design flexibility, but the average ripple varies across sampling intervals causing increased noise
Solution Approach 1:
The patent changes the temporal parameter relationship between the pixel clock signal and charge pump clock signal from independent to synchronized. Specifically, it establishes that the pixel clock signal is synchronized with the charge pump clock signal, ensuring that sampling intervals are aligned with the periodic ripple cycles. This parameter change transforms the unpredictable varying ripple average into a consistent pattern where the average ripple over each synchronized sampling interval equals zero, thereby eliminating the harmful noise effect while maintaining system functionality.
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 synchronization reduces noise effects on the fingerprint identification system, enhancing its performance by maintaining a consistent supply voltage during sampling intervals.
Implementation Method 1
The charge pump circuit receives a charge pump clock signal clk_cp to output a supply voltage V supply ' to the pixel circuit. Unavoidably, the supply voltage generated by the charge pump circuit has a ripple rp'
Implementation Method 2
The pixel circuit would convert a touch capacitance, formed between the pixel circuit and the finger, as the pixel output signal
Data Source
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AI summary
The present invention provides a fingerprint identification system includes a charge pump circuit configured to generate a supply voltage, wherein the charge pump circuit receives a first clock signal; a pixel circuit, forming a touch capacitance , determining whether the pixel circuit is corresponding to a finger valley or a finger ridge according to the touch capacitance, wherein the pixel circuit receives a second clock signal and the supply voltage; and a clock generating circuit, configured to generate the first clock signal and the second clock signal; wherein the first clock signal is related to the second clock signal.