Waveform Generator Circuit for Display-Noise-Resistant Touch Sensing
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Solution Overview
Problem
Current proximity sensor devices face challenges in accurately determining positional information due to interference from display update signals, which changes frequently and is difficult to measure and compensate for using existing approaches.
Innovation Solution
A waveform generator circuit is introduced, comprising accumulator, truncation, and saturation circuitry, that generates a finely tunable sensing frequency and waveform shape to access RAM samples, allowing for flexible interference immunity and improved capacitive sensing by adjusting clock cycles and phase increment values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If display update signals are used for display refresh, then display functionality is maintained, but interference with proximity sensing accuracy increases
Solution Approach 1:
The patent extracts the harmful display update interference from the sensing signal by using separate clock cycles for display updates and sensing operations. The waveform generator creates distinct time windows where display signals and sensing signals do not overlap, effectively removing the interference component while preserving display functionality.
Solution Approach 2:
The patent implements periodic sensing operations at specific intervals that are synchronized with display update cycles. By using a programmable waveform generator to create periodic test signals at predetermined frequencies, the system performs sensing operations during designated time windows that avoid display update periods, thereby eliminating interference while maintaining both functions.
2Adaptability or versatility
If fixed sensing frequency is used, then circuit design is simplified, but interference immunity becomes limited
Solution Approach 1:
The patent transforms the fixed frequency sensing approach into a dynamic, programmable system. The waveform generator allows real-time adjustment of sensing frequency and waveform characteristics through programmable parameters, enabling the system to adapt to different interference conditions and optimize performance for various sensing scenarios.
Solution Approach 2:
The patent implements programmable control over multiple waveform parameters including frequency, amplitude, and timing characteristics. By allowing dynamic modification of these parameters, the system can select optimal sensing frequencies that avoid display update interference and adjust waveform shapes to maximize signal-to-noise ratio under different operating conditions.
3Measurement precision
If high frequency sensing is used, then positional information resolution is improved, but susceptibility to electromagnetic interference increases
Solution Approach 1:
The patent enables dynamic adjustment of sensing frequency as a controllable parameter. The system can select from multiple frequency options to optimize the trade-off between positional resolution and interference susceptibility, choosing higher frequencies when precision is critical and lower frequencies when electromagnetic environment is noisy.
Solution Approach 2:
The patent uses periodic sensing bursts separated by integration periods where no sensing signal is active. This allows the system to accumulate signals over multiple periods while avoiding continuous high-frequency operation that would increase electromagnetic susceptibility, thereby maintaining precision while reducing interference exposure.
Data Source
AI summary
Embodiments disclosed herein generally relate to electronic devices, and more specifically, to a waveform generation circuit for input devices. One or more embodiments provide a new waveform generator for an integrated touch and display driver (TDDI) and methods for generating a waveform for capacitive sensing with a finely tunable sensing frequency. A waveform generator includes accumulator circuitry, truncation circuitry, and saturation circuitry. The accumulator circuitry is configured to accumulate the phase increment value based on a clock signal, and output the accumulated phase increment value. The truncation circuitry configured to drop one or more bits of the accumulated phase increment value to output a truncated value. The saturation circuitry is configured to compare the truncated value to a saturation limit and output a signal corresponding to accessed data samples.