Analog Front-End Channel Driver With Sigma-Delta Touch Sensing
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Solution Overview
Problem
Projected capacitive touch sensors face challenges in accurately determining touch locations due to large parasitic capacitances, which require multiple integration cycles, increasing the time to make a determination and affecting user experience, especially in larger displays.
Innovation Solution
A channel driver circuit that employs a differential module, sigma-delta module, and driver module to generate a low impedance virtual signal and receive load-modified signals, while simultaneously detecting changes, using noise shaping to reduce noise and improve signal accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple integration cycles are used to overcome large parasitic capacitances, then measurement precision is improved, but response time increases
Solution Approach 1:
The patent changes the integration method from multiple sequential integration cycles to a single integration cycle with modified circuit parameters. The differential module and sigma-delta module adjust circuit parameters to achieve accurate touch detection in a single cycle, thereby improving response time while maintaining measurement precision.
Solution Approach 2:
The patent replaces the traditional multi-cycle integration approach with a noise shaping technique using a sigma-delta module. This substitution transforms the measurement mechanism from time-based multiple sampling to a frequency-based noise shaping approach, enabling accurate detection in a single integration cycle.
2Measurement precision
If noise shaping is applied to reduce noise and improve signal accuracy, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent merges the differential amplification function and sigma-delta noise shaping function into an integrated module. By combining these functions in a single module, the patent achieves noise reduction and signal accuracy improvement while minimizing the increase in device complexity through functional integration.
Solution Approach 2:
The differential module serves multiple functions: it provides differential amplification for signal conditioning and simultaneously works with the sigma-delta module to implement noise shaping. This multi-functionality reduces the need for separate dedicated circuits, thereby limiting the increase in device complexity.
Data Source
AI summary
A channel driver circuit includes a differential module and a driver module. In some examples, the channel driver circuit also includes a sigma-delta module. The differential module receives, via a single node of a load, a channel driving signal that is provided to the load at the single node (e.g., that is based on an electrical characteristic of the load) and generates an analog error signal that is based on the channel driving signal and a reference signal. The driver module is coupled to the differential module and generates the channel driving signal based on the analog error signal or a digital error signal corresponding to the analog error signal and transmits the channel driving signal via the single node to the load. The channel driver circuit simultaneously transmits the channel driving signal to the load at the single node and senses the channel driving signal at the single node.