Capacitive Transducer On-Chip Testing via Intermediary Capacitor
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Solution Overview
Problem
The challenge lies in testing capacitive transducers, such as MEMS devices, without applying a physical stimulus or direct electrical contact to sensitive nodes, while ensuring the test does not damage the electronic circuitry and does not require complex additional circuitry, especially in high-volume production where size constraints limit access to internal nodes.
Innovation Solution
An integrated circuit with a capacitor and switching means allows for the selective application of a test signal to the transducer during a test mode, using existing capacitors on the circuit to avoid probing sensitive nodes and minimize chip-area requirements, enabling on-chip testing without burdening I/O pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If direct electrical contact is made to sensitive nodes for testing, then measurement precision is improved, but the electronic circuitry may be damaged
Solution Approach 1:
The patent introduces an intermediary capacitor that is already present in the circuit between the test signal source and the sensitive node. This capacitor acts as a buffer that allows the test signal to be applied without directly contacting the sensitive node, thus preventing damage while enabling measurement. The switching means selectively couples the test signal to the capacitor, which then transfers the signal to the node without requiring direct probe contact.
2Adaptability or versatility
If additional test circuitry is added to enable on-chip testing, then testing capability is improved, but device complexity increases
Solution Approach 1:
The patent makes existing circuit components multi-functional by enabling the capacitor and switching means to serve both their original function and a testing function. The capacitor that is already part of the signal path is reused as the test signal coupling element, and the switching means (which could be an existing switch or transistor in the circuit) is configured to selectively couple test signals. This approach enables testing capability without adding dedicated test-only components, thus improving versatility while minimizing complexity increase.
Solution Approach 2:
The circuit uses its own existing components (capacitor and switching elements) to perform the testing function, rather than requiring external test equipment or additional dedicated test circuitry. The switching means is controlled to selectively couple the test signal through the existing capacitor structure, allowing the circuit to test itself using resources already available within the device.
3Measurement precision
If physical stimulus is applied to test the transducer, then measurement precision is improved, but the transducer may be damaged or wear
Solution Approach 1:
The patent replaces mechanical or physical stimulus methods with an electrical testing approach. Instead of applying physical forces, pressure, or mechanical displacement to test the transducer, the invention uses electrical test signals that are coupled through the existing capacitor to characterize the transducer's electrical response. This substitution of mechanical testing with electrical testing maintains measurement precision while eliminating mechanical wear and damage risks.
4Ease of operation
If I/O pads are used for testing, then ease of operation is improved, but the number of available I/O pads is reduced for functional signals
Solution Approach 1:
The patent enables existing I/O pads to serve dual purposes: functional signal transmission and test signal input/output. The switching means is configured to route test signals through existing I/O pads and internal circuit paths, allowing the same pads to be used for both operational and testing functions. This eliminates the need for dedicated test pads, improving ease of operation while maximizing the utilization of limited I/O resources.
Data Source
AI summary
A method of testing a capacitive transducer circuit, for example a MEMS capacitive transducer, by applying a test signal via one or more capacitors provided in the transducer circuit.