Capacitive Pointer Detection Using Complementary Code Synthesis
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive coupling type pointer detection apparatuses face challenges in enhancing the Signal-to-Noise (S/N) ratio and maintaining tracking property when using long code lengths for signal transmission, leading to incorrect detection of pointer positions due to ghost signals and dc offset components.
Innovation Solution
The apparatus combines two kinds of codes with a predetermined relationship to form a transmission signal, using a signal supplying circuit to generate and supply these codes to conductors, and a correlation arithmetic operation circuit to calculate and synthesize correlation values, effectively canceling out ghost signals and dc offset components, thereby improving the S/N ratio without impairing tracking property.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the code length of transmission signals is increased to enhance the S/N ratio, then the S/N ratio is improved, but ghost signals and dc offset components cause incorrect detection of pointer positions
Solution Approach 1:
The patent converts the harmful ghost signals and dc offset components into beneficial elements by using complementary codes. The second code is designed as the inverse of the first code, causing ghost signals and dc offsets generated during correlation calculation to have opposite polarities. When the correlation values from both codes are synthesized, these error components cancel each other out, transforming the harmful interference into a self-correcting mechanism that enhances detection accuracy.
Solution Approach 2:
The patent segments the transmission signal into two separate code components (first code and second code) that are transmitted alternately. Each code is processed independently through correlation calculation, and their results are synthesized. This segmentation allows the system to maintain the benefits of long code length for S/N ratio improvement while using the complementary relationship between the two code segments to eliminate detection errors.
2Measurement precision
If the code length is extended to improve S/N ratio, then signal detection capability is enhanced, but tracking property deteriorates due to increased repeating period
Solution Approach 1:
The patent employs periodic transmission of complementary code pairs, where the first code and second code are transmitted in alternating periods. This periodic structure maintains a manageable repeating period despite using long codes, as each code segment completes its transmission cycle independently. The regular alternation between complementary codes ensures that the system can track pointer movements effectively while still benefiting from the enhanced S/N ratio provided by the long code length.
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 approach enhances the S/N ratio and maintains accurate pointer detection even with long code lengths, ensuring precise tracking of pointer positions by canceling out ghost signals and dc offset components.
Implementation Method 1
a variation of a capacitive coupling state between a sensor electrode and a pointer, such as a finger or a capacitive pen, is detected to detect the position of the pointer
Data Source
AI summary
A pointer detection apparatus includes a conductor pattern formed of intersecting first and second conductors. A signal supplying circuit generates transmission signals each comprised of a first code and a second code having an equal code length and having a predetermined relationship to each other, and supplies the generated transmission signals to the first conductors. A signal detection circuit is connected to the second conductors and detects reception signals, at least one of which corresponds to a variation of capacitance between the conductor pattern and a pointer. A correlation arithmetic operation circuit calculates, for each of the reception signals, first and second correlation values between the reception signal and first and second correlation value arithmetic operation signals corresponding to the first and second codes, respectively. A synthesis circuit calculates, for each pair of the first and second correlation values, a synthesis correlation value, based on which the pointer is detected.