Touch Panel RX/TX Self-Test Circuit for Safe Parallel BIST
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Solution Overview
Problem
Existing built-in self-tests (BISTs) for functional safety in touch sensing applications face challenges with high-voltage TX and standard RX I/O circuits, lacking parallelism, exhibiting long scan times, and unsafe voltage exposure, which are not robust or time-efficient.
Innovation Solution
Incorporating DFT hardware within each RX and TX circuit, including capacitors to model electrode capacitance, allowing for self-testing of both TX and RX sensing hardware circuits, with control logic to ensure safe operation and fault detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing built-in self-tests (BISTs) are used for functional safety in touch sensing applications, then safety testing can be performed, but the scan times are long and the testing is not time-efficient
Solution Approach 1:
The self-test function is segmented and integrated into each individual RX and TX circuit rather than using a separate external test system. Each circuit contains its own DFT hardware that can independently perform self-tests, allowing parallel execution of multiple tests simultaneously, thereby reducing total scan time while maintaining comprehensive safety coverage
Solution Approach 2:
DFT hardware is integrated into the RX and TX circuits during manufacturing, preparing the test capability in advance. This preliminary integration allows the circuits to perform self-tests immediately when needed, eliminating the need for external test equipment and reducing overall testing time
2Reliability
If existing built-in self-tests (BISTs) are used for functional safety in touch sensing applications, then safety testing can be performed, but the testing lacks parallelism
Solution Approach 1:
The test system is divided into independent DFT units within each RX and TX circuit. These segmented test units can operate independently and simultaneously, enabling parallel execution of multiple self-tests across different circuits, thereby increasing testing productivity and parallelism
Solution Approach 2:
Each RX and TX circuit is equipped with its own DFT hardware that performs self-testing autonomously without requiring external test equipment. This self-service capability allows multiple circuits to test themselves in parallel, significantly improving testing productivity
3Reliability
If existing built-in self-tests (BISTs) are used for functional safety in touch sensing applications, then safety testing can be performed, but the voltage exposure is unsafe
Solution Approach 1:
Capacitors are introduced as intermediary elements to model electrode capacitance during self-tests. These capacitors serve as safe substitutes for the actual high-voltage TX electrodes, allowing the RX circuits to be tested without exposing them to dangerous high voltages, thereby eliminating the harmful voltage exposure while maintaining test validity
4Reliability
If DFT hardware is integrated within each RX and TX circuit, then self-testing capability is improved, but the device complexity increases
Solution Approach 1:
The DFT hardware is merged with the existing RX and TX circuits rather than being added as separate external components. This integration combines the testing function with the operational circuits, reducing overall system complexity by eliminating redundant test equipment while maintaining comprehensive self-testing capability
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
Enables robust, time-efficient, and safe self-testing of TX and RX circuits, minimizing false touch detection and ensuring compliance with Automotive Safety and Integrity (ASIL) requirements.
Implementation Method 1
Incorporating DFT hardware within each RX and TX circuit, including capacitors to model electrode capacitance
Implementation Method 2
When a conductive object, such as a finger, comes in contact or close proximity with the touch-sensing surface, the capacitance of one or more capacitive touch sensor elements changes
Implementation Method 3
When a finger touches a sensor element or is in close proximity to the sensor element, the capacitive coupling between the receiver and the transmitter of the sensor element is decreased as the finger shunts part of the electric field to ground
Data Source
AI summary
A device includes a signal bus to carry a sinusoidal drive signal and receive (RX) sensing hardware, coupled to an electrode of a touch panel, including an attenuator configured to detect a touch signal from the electrode, a multiplexer coupled between an input to the attenuator and the signal bus, and a capacitor coupled between the signal bus and the multiplexer. Control logic is coupled to the RX sensing hardware to perform a self-test, including to disconnect the RX sensing hardware from the electrode, cause the multiplexer to couple the capacitor to the input of the attenuator, determine whether an output of the RX sensing hardware is within a functional operating range.