Active RF Noise Cancellation for Touch Screen EMC Compliance
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Solution Overview
Problem
Touch screen displays, particularly those used in point of sale terminals and ATMs, face challenges in meeting higher electromagnetic compatibility (EMC) standards due to susceptibility to radio frequency noise, which causes false touch indications and operational failures.
Innovation Solution
A radio frequency noise reduction device comprising a first and second bandpass filter, and a variable gain amplifier is used to isolate and cancel noise on separate power planes, with the output signal from the amplifier being 180 degrees out of phase and matching the noise's amplitude to effectively cancel it on the second power plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If certain touch technologies are used to achieve good light transmission characteristics, then light transmission is improved, but the system becomes susceptible to radio frequency noise causing false touch indications
Solution Approach 1:
The patent captures the radio frequency noise that would otherwise cause false touch indications and converts it into a useful signal. By detecting the noise characteristics on one power plane and actively generating an anti-phase signal, the system transforms the harmful noise into a beneficial cancellation signal that is injected back to neutralize the original noise, thereby maintaining both good light transmission and noise immunity
Solution Approach 2:
The patent introduces an intermediary noise cancellation system that includes bandpass filters, variable gain amplifiers, and signal injection circuits. This intermediary system sits between the noise source and the touch detection circuitry, actively processing the noise signal and injecting a corrected version that eliminates the harmful effects while preserving the intended touch signals
2Reliability
If higher EMC compliance standards are met to ensure reliability in financial transactions, then system reliability is improved, but device complexity increases
Solution Approach 1:
The noise cancellation system is self-regulating and automatically adapts to varying noise conditions without external intervention. The variable gain amplifier continuously monitors the noise level on the second power plane and adjusts its gain accordingly, while the bandpass filters automatically track the noise frequency characteristics, enabling the system to maintain high EMC compliance dynamically without complex manual configuration or external control
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 solution dynamically identifies and reduces radio frequency noise, preventing false signals and ensuring the touch screen display meets higher EMC standards by eliminating noise interference, thus ensuring reliable operation and compliance with safety and security requirements.
Implementation Method 1
the output signal of the variable gain amplifier has the frequency spectrum of the radio frequency noise on the first power plane shifted in phase by 180 degrees
Implementation Method 2
a first bandpass filter adapted to receive a first signal from a first power plane and output only a first predetermined band of radio frequencies
Data Source
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AI summary
A radio frequency noise reduction device (270) and methods of operation thereof are described. The radio frequency noise reduction device (270) identifies radio frequency noise on an isolated power plane (206) of an electronic apparatus (100) and generates an electrical signal (256) that is injected into the isolated power plane (206) and cancels the identified radio frequency noise. The generated electrical signal (256) matches the frequency spectrum and amplitude of the identified radio frequency noise but the phase of the generated electrical signal (256) is shifted by 180 degrees from the identified radio frequency noise.