Pixel Sensing Circuit Noise Detection Mode Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive fingerprint identification systems face accuracy issues due to parasitic capacitors and noise interference, which affect the detection of capacitance variations and require complex clock pulse signal modifications for different noise frequencies.
Innovation Solution
A pixel sensing circuit with a capacitance sensing layer, shielding layers, and a charging circuit that can switch between fingerprint identification and noise detection modes, using positive and negative voltage modes to isolate the capacitance sensing layer and selectively detect noise frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metal layer is arranged under the capacitance sensing layer to achieve shielding effect, then circuit interference is prevented, but a parasitic capacitor is formed between the capacitance sensing layer and the metal layer, which lowers the accuracy of fingerprint identification
Solution Approach 1:
An insulating layer is introduced as an intermediary between the capacitance sensing layer and the metal shielding layer. This insulating layer prevents direct electrical contact that would create parasitic capacitance, while still allowing the metal layer to provide electromagnetic shielding. The insulating layer acts as a mediator that enables both shielding functionality and measurement accuracy to coexist.
Solution Approach 2:
The shielding structure is segmented into multiple functional layers: the capacitance sensing layer, an insulating layer, and a metal shielding layer. This segmentation separates the sensing function from the shielding function, allowing each layer to perform its specific role without interfering with the other, thus eliminating parasitic capacitance while maintaining shielding effectiveness.
2Adaptability or versatility
If different pixel sensing circuits use different clock pulse signals to detect noise at different frequencies, then noise detection capability is improved, but circuit complexity and difficulty of practice increase
Solution Approach 1:
A single pixel sensing circuit is designed to perform multiple functions: fingerprint identification and noise detection at different frequencies. By making the circuit universal and configurable, the patent eliminates the need for separate dedicated circuits for each function, thereby reducing overall system complexity while maintaining full noise detection capability across different frequency ranges.
Solution Approach 2:
The pixel sensing circuit employs dynamic switching between different operating modes (fingerprint identification mode and noise detection modes). Through dynamic control of the charging circuit and clock pulse signals, the same hardware circuit can adaptively change its function based on operational requirements, enabling multi-frequency noise detection without requiring separate static circuits for each frequency.
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
Improves fingerprint identification accuracy by reducing parasitic capacitor interference and enabling selective noise detection, enhancing the overall performance of the fingerprint identification system.
Implementation Method 1
Capacitive fingerprint identification is a well-populated fingerprint identification mode, which judges the ridges and valleys of a user by sensing variations of the capacitance
Implementation Method 2
a metal layer is arranged under the capacitance sensing layer to achieve a shielding effect and thus prevent the circuits under the metal layer from causing interference to the capacitance sensing layer
Implementation Method 3
a parasitic capacitor may be formed between the capacitance sensing layer and the metal layer, and the capacitance of the parasitic capacitor is generally greater than the capacitance of a contact capacitor generated by contact of the finger
Data Source
AI summary
Disclosed is a pixel sensing circuit, which is in a fingerprint identification mode or a noise detection mode, and includes: a plurality of shielding layers, including a first-type shielding layer and a second-type shielding layer, the second shielding layer being coupled to a ground terminal; and a charging circuit, coupled to the capacitance sensing layer and the first-type shielding layer, and comprising a positive voltage generator configured to providing a positive voltage; wherein when the pixel sensing circuit is in a fingerprint identification mode, the charging circuit periodically provides the positive voltage for the capacitance sensing layer and the first-type shielding layer; or when the pixel sensing circuit is in the noise detection mode, the charging circuit cuts off connections between the positive voltage generator and the capacitance sensing layer and the first-type shielding layer, and periodically outputs a voltage of the capacitance sensing layer to a first output terminal.