Single-Ended Sigma-Delta Modulator for Touch Sensing SNR
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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, especially in automotive applications, which complicates capacitance measurement and increases sensor size.
Innovation Solution
Implementing a sigma-delta modulator (SDM) with a single-ended architecture in the capacitive measurement channel, reducing the number of operational amplifiers, switches, and capacitors, and using current-balancing chains to simplify the design and reduce channel size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a traditional multi-amplifier SDM architecture is used, then measurement precision and noise immunity are improved, but device complexity and channel size increase
Solution Approach 1:
The patent extracts and removes redundant operational amplifiers from the traditional multi-amplifier SDM architecture, retaining only a single operational amplifier while achieving comparable or superior performance through optimized circuit topology and signal processing techniques
Solution Approach 2:
The patent combines multiple functions previously performed by separate operational amplifiers into a single operational amplifier, integrating signal amplification, filtering, and modulation functions into one unified circuit block, thereby reducing device complexity while maintaining measurement precision
2Measurement precision
If more operational amplifiers and capacitors are used in SDM, then SNR is improved, but sensor area and channel size increase
Solution Approach 1:
The patent changes key circuit parameters including capacitor values, resistor ratios, and operating frequencies to optimize performance with minimal components, achieving high SNR through parameter optimization rather than component proliferation
Solution Approach 2:
The patent employs dynamic switching techniques and time-multiplexed operation to maximize the utilization of the single operational amplifier, allowing it to perform multiple functions sequentially at high speed, thereby achieving performance equivalent to static multi-amplifier architectures with dynamic component usage
3Measurement precision
If excitation energy is increased to improve SNR, then measurement precision is improved, but emission from touch panel sensor increases
Solution Approach 1:
The patent implements feedback mechanisms in the single-amplifier SDM architecture that dynamically adjust signal processing gain and filtering based on measured signal conditions, extracting maximum information from low-energy excitation signals while maintaining high SNR through adaptive signal enhancement rather than increased excitation power
Solution Approach 2:
The patent replaces physical signal amplification (increasing excitation energy) with electronic signal processing techniques including digital filtering, correlation detection, and spectral analysis that enhance SNR through information processing rather than energy amplification, thereby avoiding increased electromagnetic emission
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.