Random-Reference Output Conversion for Linear Fingerprint Signals
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Solution Overview
Problem
Fingerprint identification systems face challenges in achieving good statistical linearity of output signals due to noise, which affects back-end image processing and security in portable devices.
Innovation Solution
An output conversion circuit comprising a comparator, counter, and a reference signal generator that uses a random digit generator to create a varying reference signal, converting a first output signal with poor statistical linearity into a second output signal with improved linearity by accumulating comparison outputs, facilitating better image processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pixel array circuit converts capacitance into a pixel output signal, then fingerprint detection is enabled, but the output signal has poor statistical linearity due to noise
Solution Approach 1:
The patent introduces a reference signal as an intermediary element to mediate between the noisy pixel output signal and the quantization process. The reference signal, which varies randomly over time, serves as a mediator that when subtracted from the pixel output signal, transforms the noise distribution into a more uniform statistical characteristic, thereby improving linearity without eliminating the noise itself
Solution Approach 2:
The patent changes the parameter of the reference signal over time, specifically making it a time-varying random signal rather than a fixed value. This parameter change allows the reference signal to interact with the noise in the pixel output signal in a way that produces a difference signal with improved statistical linearity, transforming the noise characteristics through temporal variation
2Measurement precision
If a fixed reference value is used in the comparator, then the circuit structure is simple, but the output signal maintains poor statistical linearity
Solution Approach 1:
The patent replaces what would traditionally be a simple fixed voltage reference (analog/membrane-based) with a digitally-generated reference signal. By using a digital random number generator and digital-to-analog converter, the system substitutes complex digital circuitry for a simple analog reference, achieving improved signal linearity through computational randomness rather than physical reference stability
3Measurement precision
If the reference signal is fixed, then the comparator operation is straightforward, but the quantization produces biased results due to noise
Solution Approach 1:
The patent makes the reference signal dynamic rather than static. The reference signal continuously varies over time according to a random distribution, which causes the quantization threshold to shift dynamically. This dynamic behavior prevents consistent bias in the quantization results by ensuring that noise-induced errors are distributed more uniformly across the measurement range over time
Data Source
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AI summary
The present invention provides an output conversion circuit and a fingerprint identification system. The output conversion circuit includes: a comparator, a counter, and a reference signal generator, where the counter includes: a first input end, configured to receive a first output signal; a second input end; and an output end, configured to generate a comparison output signal; the counter is connected to the output end of the comparator, and configured to generate a second output signal; and the reference signal generator is connected to the second input end, and configured to generate a reference signal, where the reference signal generator includes a random digit generator configured to generate a random digit, and the reference signal is associated with the random digit; where the comparator generates the comparison output signal according to the first output signal and the reference signal. The output conversion circuit provided in the present invention has an advantage of improving statistical linearity of an output signal.