Single-Ended Sigma-Delta Modulator for Compact Touch Sensing
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Solution Overview
Problem
Existing capacitive touch sensing systems face challenges in achieving high signal-to-noise ratio (SNR) due to limited excitation energy and interference from display components, inductive loads, and electromagnetic noise, particularly in automotive applications, which complicates accurate capacitance measurements.
Innovation Solution
Implementing a sigma-delta modulator (SDM) with a single-ended architecture in the analog frontend, reducing the size and complexity of capacitive measurement channels by using single-ended operational amplifiers and minimizing the number of switches and capacitors, while maintaining operational ability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a traditional multi-channel capacitive measurement system is used, then measurement coverage is sufficient, but channel size and silicon area consumption are large
Solution Approach 1:
The patent extracts and removes unnecessary components from the traditional capacitive measurement channel, specifically eliminating redundant switches and capacitors by using a streamlined architecture with a single switching node and a single capacitor, thereby reducing silicon area while maintaining measurement functionality
Solution Approach 2:
The patent merges multiple functions into fewer components, combining the roles of multiple switches into a single switching node and integrating multiple capacitor functions into one capacitor, reducing the overall channel size and silicon area consumption
2Measurement precision
If excitation energy is increased to improve SNR, then signal-to-noise ratio improves, but power consumption increases
Solution Approach 1:
The patent changes the operational parameters of the capacitive measurement system by using optimized switching sequences and signal processing techniques that achieve high SNR through intelligent signal modulation rather than brute-force energy increase, thereby maintaining measurement precision while controlling power consumption
3Adaptability or versatility
If display components and inductive loads are present, then functionality is complete, but electromagnetic interference increases
Solution Approach 1:
The patent converts the harmful electromagnetic interference from display components and inductive loads into a manageable signal characteristic by using differential measurement techniques and correlated double sampling that distinguish the desired capacitive signal from the electromagnetic noise, effectively transforming the interference problem into a solvable signal processing task
Data Source
AI summary
An integrated circuit includes a sigma-delta modulator coupled to a receive electrode of a capacitive touch screen sensor and including a first single-ended integrator and a second single-ended integrator selectively coupled to an output of the first single-ended integrator. A latch is coupled to an output of the second single-ended integrator and driven by a frequency modulation signal. A balancing circuit is selectively coupled to a first input of the first single-ended integrator and to a second input of the second single-ended integrator. Logic is coupled to the balancing circuit and causes, based on the frequency modulation signal and an output value of the latch, the balancing circuit to one of: apply a positive balancing current to the first input and a negative balancing current to the second input; or apply a positive balancing current to the second input and a negative balancing current to the first input.