Acoustic Touch Auto-Gain Switching for Low-Signal A/D Precision
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Solution Overview
Problem
Acoustic touch systems face challenges in accurately detecting touch events due to a broad voltage range at the input of the A/D converter, leading to quantization errors and incorrect interpretations, especially when voltages are at the low end or exceed the maximum operating range.
Innovation Solution
An auto-gain switching module adjusts the gain levels of analog input signals from an acoustic touch pad based on their signal levels, ensuring that the signals fall within the operating range of the A/D converter, thereby reducing quantization errors and improving the detection of touch events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the operating range is set to accommodate the highest maximum voltage level, then the maximum voltage level can be fully captured, but voltages at the low end of the scale may not register and/or suffer significantly from quantization error
Solution Approach 1:
The patent implements dynamic gain adjustment where the gain value is changed based on the signal level. The system automatically selects between different gain values (e.g., first gain value for higher signal levels, second gain value for lower signal levels) to optimize the A/D converter's operating range. This dynamic adaptation allows the system to maintain measurement precision across varying signal amplitudes without requiring multiple fixed-range converters.
Solution Approach 2:
The system changes the gain parameter of the A/D converter based on the input signal characteristics. By monitoring the signal level and adjusting the gain accordingly, the system transforms a fixed-parameter system into a variable-parameter system that can optimize its performance for different operating conditions, thereby resolving the contradiction between capturing high voltage levels and maintaining precision at low voltage levels.
2Adaptability or versatility
If the operating range is set to accommodate the highest maximum voltage level, then the full voltage range can be captured, but when the input exceeds the maximum level the output is 'railed' and frequency domain analysis produces a 'splatter' across the spectrum
Solution Approach 1:
The system dynamically adjusts the gain before the A/D conversion based on the input signal amplitude. When high gain is applied, the effective input range is reduced, preventing rail saturation. This dynamic range adaptation ensures that the converter operates within its linear region regardless of the absolute input signal level, thereby maintaining reliable touch event recognition while handling varying voltage ranges.
Solution Approach 2:
The system employs feedback mechanisms where the output or a monitoring signal is used to determine the appropriate gain setting. By continuously monitoring the signal level and adjusting the gain accordingly, the system prevents overload conditions that would cause rail saturation and spectral splatter, thus maintaining reliability across different input conditions.
3Measurement precision
If multiple gain elements are provided to handle different signal levels, then quantization error is reduced, but the device complexity increases
Solution Approach 1:
The system segments the signal processing path by providing multiple gain elements (e.g., first gain element, second gain element) that can be selectively applied. Each gain element is optimized for specific signal level ranges, allowing the system to divide the overall dynamic range into manageable segments. This segmentation enables precise measurement across different voltage ranges while keeping each individual gain stage relatively simple.
Solution Approach 2:
The gain switching module serves multiple functions: it acts as a signal amplifier for low-level inputs, a signal attenuator for high-level inputs, and an automatic range selector. By integrating these multiple functions into a single control module that automatically selects the appropriate gain based on signal level, the system achieves high measurement precision without proportionally increasing overall device complexity.
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
The solution enhances the robustness of touch event detection and reduces quantization errors by dynamically adjusting gain levels, allowing for accurate interpretation of touch events across a wide range of signal amplitudes.
Implementation Method 1
A plurality of gain elements receive the analog input signal and output gain-adjusted analog signals
Data Source
AI summary
An apparatus for processing signals received from an acoustic touch surface comprises an analog input receiving an analog input signal having a signal level. The analog input signal comprises data indicative of a touch location on a touch surface. A plurality of gain elements receive the analog input signal and output gain-adjusted analog signals. A gain selection module selects one of the gain-adjusted analog signals based on the signal level of the analog input signal.