Touch Controller Analog Front End for Noise Immunity and Small Die Area
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Solution Overview
Problem
Touch sensor panels face challenges in achieving improved charge handling capability and noise immunity while maintaining a small footprint, as existing technologies often require significant DIE real estate and struggle with noise attenuation.
Innovation Solution
The implementation of a transimpedance amplifier with a programmable feedback resistor and a bandpass filter, coupled with an anti-aliasing filter or sigma-delta analog to digital converter, to enhance noise attenuation and reduce real estate consumption, along with the use of multiplexors to manage multiple analog inputs efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge amplifier with capacitive feedback is used, then charge handling capability is improved, but DIE real estate consumption increases
Solution Approach 1:
The patent replaces the traditional charge amplifier with a transimpedance amplifier that uses resistive feedback instead of capacitive feedback. This substitution changes the fundamental operating mechanism from charge-based to current-based processing, achieving comparable charge handling capability while reducing the area required for capacitor storage elements.
Solution Approach 2:
The patent changes the feedback parameter from capacitance to resistance. By using a resistive feedback network in the transimpedance amplifier instead of a capacitive feedback network in the charge amplifier, the system achieves different operational characteristics that reduce area consumption while maintaining signal processing capability.
2Object-affected harmful factors
If noise attenuation is improved, then noise immunity is enhanced, but device complexity increases
Solution Approach 1:
The patent employs feedback mechanisms in the transimpedance amplifier to achieve noise attenuation. The resistive feedback network provides signal conditioning that inherently suppresses noise while maintaining system stability, avoiding the need for additional complex noise filtering stages.
Solution Approach 2:
The transimpedance amplifier acts as an intermediary stage that converts capacitive coupling signals from the touch sensor into voltage signals suitable for subsequent digital processing. This intermediate conversion stage provides natural noise filtering by operating at optimal impedance levels for the following circuit stages.
3Measurement precision
If the number of analog inputs is increased, then touch sensor resolution is improved, but DIE real estate consumption increases
Solution Approach 1:
The transimpedance amplifier is designed as a universal input stage that can handle multiple analog inputs from different touch sensor configurations (self-capacitance, mutual capacitance, different grid arrangements) through a single standardized interface, eliminating the need for separate processing circuits for each input type.
Solution Approach 2:
The patent segments the signal processing function into distinct stages: the transimpedance amplifier handles analog signal conditioning for multiple inputs, while subsequent digital signal processing handles the resolution and detection logic. This segmentation allows multiple inputs to share common analog processing hardware.
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
This configuration provides improved noise immunity and charge handling capability while minimizing the footprint, allowing for more efficient processing of touch events with reduced power consumption and increased noise headroom.
Implementation Method 1
a transimpedance amplifier in its analog front end for receiving a sense signal from a touch sensor panel
Implementation Method 2
with a feedback resistor coupled to an input of the transimpedance amplifier and to an output of the transimpedance amplifier
Implementation Method 3
The bandpass filter can increase available noise headroom in the output of the transimpedance amplifier
Implementation Method 4
The output of the bandpass filter can be input to an anti-aliasing filter, which feeds into an analog to digital converter
Implementation Method 5
the output of the bandpass filter can be input directly to a sigma-delta analog to digital converter
Data Source
AI summary
A controller for a touch sensor includes a transimpedance amplifier, and a feedback resistor coupled to an input of the transimpedance amplifier and to an output of the transimpedance amplifier. At least one multiplexor may be coupled to the input of the transimpedance amplifier and configured to multiplex a plurality of analog inputs to one dedicated channel. The controller may further include a bandpass filter coupled to the output of the transimpedance amplifier. The output of the bandpass filter may be input to an anti-aliasing filter, which feeds into an analog to digital converter. Alternatively, the output of the bandpass filter may be input to a sigma-delta analog to digital converter.