Capacitive Touch Channel SPU With CIC Filtering for High 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 interference from display components, inductive loads, and electromagnetic emissions, particularly in automotive applications, which complicates the design and increases channel size and power consumption.
Innovation Solution
A simplified signal processing unit (SPU) design that integrates a sigma-delta modulator directly with a demodulator and a low-pass filter, utilizing a cascaded integrator-comb (CIC) filter to reduce complexity and channel size, eliminating the need for a signal reconstruction filter and down sampler, and employing a second-order CIC filter to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional signal processing unit with separate signal reconstruction filter and down sampler is used, then measurement precision can be maintained, but device complexity and channel size increase
Solution Approach 1:
The patent merges the signal reconstruction filter and down sampler into a single integrated CIC filter structure. The CIC filter combines the functions of a low-pass filter and a decimator, eliminating the need for separate components while maintaining signal quality and reducing overall channel size.
Solution Approach 2:
The CIC filter performs multiple functions simultaneously: it acts as a low-pass filter to reconstruct the signal, a decimator to down sample the data, and a comb filter to eliminate imaging artifacts. This multi-functionality reduces the number of separate components needed in the signal processing unit.
2Measurement precision
If more filtering components are added to reduce interference, then signal-to-noise ratio improves, but power consumption increases
Solution Approach 1:
The patent replaces traditional analog filter components with a digital CIC filter implementation. This substitution allows for more efficient signal processing with lower power consumption, as digital filtering can be performed with simpler circuitry compared to traditional analog filter banks.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The simplified SPU design reduces channel size and power consumption while maintaining high SNR, effectively addressing the challenges of interference and complexity in capacitive touch sensing systems.
Implementation Method 1
A sigma-delta modulator (SDM) is employed in a receiver (Rx) side of the measurement channel... that is coupled to an electrode
Implementation Method 2
utilizing a cascaded integrator-comb (CIC) filter to reduce complexity and channel size
Data Source
AI summary
An integrated circuit includes a sigma-delta modulator (SDM) coupled to a receive electrode, which is selectively coupled to multiple unit cell sensors. A demodulator is coupled directly to the SDM, the demodulator to generate a multibit digital signal by demodulating a digital pulse density modulated (PDM) signal received from the SDM. The demodulating can include multiplying digitized cosine values with the digital PDM signal. A cascaded integrator-comb (CIC) filter is coupled to the demodulator and includes a first integrator and a second integrator cascaded together and to accumulate, at the second integrator, a plurality of samples of the multibit digital signal. The CIC filter includes a single comb circuit coupled to the second integrator, the single comb circuit to generate a measured amplitude bitstream from the accumulated samples.