Frequency-Selective Charge Amplifier for Common-Mode Noise Rejection
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Solution Overview
Problem
Capacitive touchscreen systems face challenges in maintaining high signal-to-noise ratio (SNR) performance due to common-mode interference from sources like displays and wireless transmitters, which often require increased power and chip area to mitigate saturation and noise degradation.
Innovation Solution
The implementation of frequency selective analog front-end circuitry, which includes complex poles to attenuate common-mode interference by selecting component values that boost the charge signal and reduce noise above the drive frequency, thereby reducing power and chip area while maintaining SNR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional charge amplifier circuitry is used to maintain high SNR performance, then signal-to-noise ratio is improved, but power consumption increases
Solution Approach 1:
The patent changes the frequency response parameters of the charge amplifier by introducing complex poles through specific RC networks. This modifies the amplifier's behavior to provide automatic gain control and frequency-dependent filtering, achieving high SNR at touch frequencies while reducing power consumption through adaptive operation rather than continuous high-power amplification.
Solution Approach 2:
The frequency-selective feedback networks ensure that the amplifier operates continuously at optimal gain only at the relevant touch detection frequencies, while automatically attenuating other frequencies. This continuous frequency-selective operation maintains SNR performance without requiring continuous high-power amplification across all frequencies.
2Measurement precision
If conventional charge amplifier circuitry is used to maintain high SNR performance, then signal-to-noise ratio is improved, but chip area increases
Solution Approach 1:
The charge amplifier circuit performs multiple functions simultaneously: it amplifies touch signals, filters common-mode interference, provides automatic gain control, and rejects noise across different frequency ranges. This multi-functionality is achieved through the frequency-selective feedback networks that combine filtering and amplification in a single integrated circuit, reducing the need for separate components and reducing overall chip area.
Solution Approach 2:
The patent merges the filtering function and amplification function into a single charge amplifier stage. The frequency-selective feedback networks combine the low-pass filter and band-pass filter functions with the amplification function, eliminating the need for separate filter circuits and reducing the total chip area required to achieve high SNR performance.
3Use of energy by moving object
If frequency selective analog front-end circuitry is used, then power consumption is reduced, but circuit complexity increases
Solution Approach 1:
The patent introduces frequency-selective parameters through RC time constants that automatically adjust the circuit's gain and filtering characteristics. By changing the frequency response parameters rather than adding complex control logic, the circuit achieves power reduction through passive frequency-dependent behavior, minimizing the increase in circuit complexity.
Solution Approach 2:
The frequency-selective feedback networks enable the circuit to automatically adjust its gain and filtering without external control. The circuit self-regulates by using the inherent frequency-dependent impedance of the RC networks to provide automatic gain control and frequency selection, reducing the need for additional control circuitry and minimizing complexity increases.
4Area of stationary object
If frequency selective analog front-end circuitry is used, then chip area is reduced, but circuit complexity increases
Solution Approach 1:
The charge amplifier with frequency-selective feedback performs multiple functions (amplification, filtering, gain control) in a single circuit stage, reducing chip area by eliminating the need for separate filter circuits and control logic. The frequency-selective feedback networks provide both filtering and amplification functions simultaneously, minimizing the total circuit complexity while achieving area reduction.
Solution Approach 2:
The patent combines the filtering and amplification functions into a single integrated charge amplifier stage with frequency-selective feedback. This merging of functions reduces chip area by eliminating redundant components while the feedback networks provide the necessary frequency selectivity without requiring additional complex control circuitry.
Data Source
AI summary
Frequency selective analog front-end circuitry, used to convert a sensed charge signal to an analog voltage is disclosed. In one aspect, the frequency selective analog front-end circuitry includes an op-amp having an output, an inverting input and a noninverting input, a first resistor connected between the terminal of the first capacitor and the inverting input of the op-amp, a second capacitor connected between the output of the op-amp and the inverting input of the op-amp, a second resistor connected between the output of the op-amp and the inverting input of the op-amp, a third capacitor connected between the terminal of the first capacitor and the noninverting input of the op-amp, and a third resistor connected between the noninverting input of the op-amp and a reference voltage.