Differential ADC Pulse-Edge Measurement for Touch Noise Rejection
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Solution Overview
Problem
Touch screens face challenges in achieving high sensitivity and ease of use due to interference from low-frequency noise, which affects the accuracy of charge transfer measurements.
Innovation Solution
The implementation of a differential analog-to-digital converter (ADC) coupled with a waveform capture circuit and a virtual earth amplifier, along with sample and hold circuits, allows for the rejection of low-frequency noise by measuring and subtracting signals from both edges of a pulse, thereby enhancing dynamic range and resolution in charge transfer measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional ADC is used for charge measurements, then the device complexity is low, but low-frequency noise interferes with measurement accuracy
Solution Approach 1:
The measurement process is segmented into two separate measurements: one for the rising edge and one for the falling edge. Each edge is measured independently by the ADC, and the results are later combined through subtraction. This segmentation allows the system to eliminate low-frequency noise while maintaining a relatively simple ADC circuit design.
Solution Approach 2:
The patent introduces an intermediary processing step where the outputs from rising edge and falling edge measurements are subtracted. This intermediary subtraction operation acts as a noise filter, removing common low-frequency components while preserving the differential signal information.
2Measurement precision
If single-edge pulse measurement is used, then the device complexity is low, but the dynamic range of charge measurements is limited
Solution Approach 1:
The measurement is divided into two separate edge measurements (rising and falling) instead of a single measurement. This segmentation doubles the effective dynamic range because the system can now measure charge transfers in both positive and negative directions, effectively utilizing the full capability of the ADC across a wider range.
Solution Approach 2:
The patent transitions from a single-dimensional measurement (one edge) to a two-dimensional measurement approach (both rising and falling edges). By measuring in both dimensions and combining the results, the system achieves doubled dynamic range without requiring a more complex ADC.
3Measurement precision
If low-frequency noise is present, then the measurement system is simple, but the sensitivity and accuracy of touch screen operations are reduced
Solution Approach 1:
The patent converts the harmful effect of low-frequency noise into a beneficial filtering mechanism. By measuring both rising and falling edges and subtracting the results, the system exploits the fact that low-frequency noise appears in both measurements to cancel it out, while the differential signal of interest is preserved and enhanced.
Solution Approach 2:
The system uses feedback by comparing the rising edge measurement with the falling edge measurement. The subtraction operation provides feedback that eliminates common-mode low-frequency noise components, thereby improving the overall measurement accuracy and sensitivity of the touch screen system.
Data Source
AI summary
Electronic apparatus and methods of operating the electronic apparatus include less than a frequency associated with a generated waveform. In various embodiments, an apparatus using a differential analog-to-digital converter can perform low frequency noise rejection that can be implemented in a variety of applications. Additional apparatus, systems, and methods are disclosed.