Differential-Difference Amplifier Touch Interface for Display Noise Rejection
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Solution Overview
Problem
Conventional touch-sensing circuits in capacitive touch panels face increasing challenges due to display noise coupling, which degrades performance and makes it difficult to provide low-noise read-out circuits effectively.
Innovation Solution
A single-stage differential-difference-amplifier-based touch event sensing approach that pre-cancels coupled display noise using common-mode rejection, generating amplified differential output signals with substantially only the desired touch sensing information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional buffering stage followed by difference amplifier stage is used, then touch sensing signals can be read out, but display noise couples into the touch-sensing layers degrading performance
Solution Approach 1:
The patent applies preliminary action by performing noise cancellation before amplification. The differential difference amplifier subtracts the common-mode display noise from adjacent channels prior to the amplification stage, preventing the noise from being amplified along with the touch signal. This pre-processing approach effectively removes the harmful noise component before it can degrade the measurement precision.
Solution Approach 2:
The patent converts the harmful display noise into a beneficial common-mode signal that can be rejected. By feeding back the differential output signals and using them to cancel the common-mode noise at the input stage, the system transforms the noise problem into a solution where the noise itself becomes the cancellation reference, improving signal-to-noise ratio.
2Power
If multi-stage amplification is used to amplify touch signals, then signal strength increases, but display noise is also amplified
Solution Approach 1:
The patent performs noise cancellation before the amplification stage by using the differential difference amplifier configuration. The feedback paths from the differential outputs are used to subtract the common-mode noise component from the input signals before amplification occurs, ensuring that only the differential touch signal is amplified while the common-mode noise remains rejected.
Solution Approach 2:
The patent segments the amplification function into two distinct operations: first, noise cancellation through common-mode rejection in the differential difference amplifier stage; second, signal amplification through the differential gain stage. This segmentation ensures that amplification is applied only to the desired differential signal rather than to the sum of signal and noise.
3Object-affected harmful factors
If single-stage differential-difference-amplifier is used, then display noise is pre-cancelled, but circuit complexity increases
Solution Approach 1:
The patent merges multiple functions into a single differential difference amplifier stage. The circuit combines the difference amplifier function (for noise rejection) and the differential amplifier function (for signal amplification) into one integrated stage with feedback paths. This consolidation achieves both noise cancellation and signal amplification simultaneously, reducing the need for separate multi-stage circuits while maintaining performance.
Solution Approach 2:
The differential difference amplifier stage performs multiple functions: it rejects common-mode display noise, amplifies the differential touch signal, and provides feedback-based noise cancellation. This multi-functional design eliminates the need for separate buffering and difference amplifier stages, reducing overall circuit complexity while achieving superior noise rejection.
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 effectively reduces the majority of coupled display noise, improving the signal-to-noise ratio and enhancing the accuracy of touch event sensing in capacitive touch panels.
Implementation Method 1
a single-stage, differential-difference-amplifier-based touch event sensing approach that pre-cancels coupled display noise from adjacent channels by common-mode rejection prior to amplifying
Data Source
AI summary
Techniques are described for touch event sensing in a capacitive touch panel that is integrated with a display. In some such environments, a large amount of display noise is capacitively coupled with the touch sensing signals. This can degrade performance of conventional sensing approaches, which tend to use a buffering stage followed by a difference amplifier stage. Embodiments provide a single-stage, differential-difference-amplifier-based touch event sensing approach that pre-cancels coupled display noise from adjacent channels by common-mode rejection prior to amplifying, thereby generating amplified differential output signals that include substantially only the desired touch sensing information.