Capacitance Sensing Circuit for IC Pin Testing
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Solution Overview
Problem
There is a need for a simple and inexpensive method to test the capacitance of a circuit coupled to an output of an IC chip, as existing methods lack efficiency and complexity.
Innovation Solution
A capacitance sensing circuit comprising an amplifier, comparator, and counter is integrated into an IC chip, which generates an output voltage and compares it to a reference voltage to determine the capacitance of a load device connected to the IC pin by measuring the response delay, using a current source to control the charge current and an offset voltage to ensure accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a capacitance testing circuit is integrated into an IC chip, then the measurement capability and automation are improved, but the device complexity increases
Solution Approach 1:
The patent combines the capacitance testing function with the existing IC chip output structure by integrating a testing circuit that shares the output pin. The amplifier, comparator, and counter are merged into a single integrated testing unit that can operate within the existing chip architecture, reducing the need for separate external testing equipment.
Solution Approach 2:
The output pin of the IC chip is designed to serve dual purposes: normal operational output and capacitance testing. The testing circuit can be activated to perform capacitance measurements on connected load devices without requiring dedicated separate pins or external equipment, making the chip universally capable of both operation and self-testing.
2Ease of manufacture
If a simple testing circuit is used, then the ease of manufacture and device complexity are improved, but the measurement precision may be compromised
Solution Approach 1:
The testing circuit employs a feedback mechanism where the comparator continuously monitors the voltage across the capacitor and compares it against a reference voltage. This feedback loop enables precise determination of when the capacitor reaches the reference voltage, allowing for accurate capacitance measurement through the counter while maintaining a relatively simple circuit structure.
Solution Approach 2:
The patent replaces complex manual measurement procedures with an automated electronic system using an amplifier, comparator, and counter. This substitution of mechanical/manual testing with electronic automation achieves both simplicity in implementation and high measurement precision, as the electronic components can perform rapid, accurate measurements without human intervention.
3Measurement precision
If the output pin is disconnected from the amplifier during testing, then the measurement accuracy is improved, but the productivity and testing time are reduced
Solution Approach 1:
The testing circuit operates by periodically disconnecting the output pin from the amplifier during the measurement phase, then reconnecting it for normal operation. This periodic disconnection allows for accurate capacitance measurements to be taken at specific intervals without permanently interrupting the functionality of the IC chip, balancing measurement needs with operational continuity.
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 solution allows for efficient and accurate determination of capacitance, enabling the IC chip to determine if a load device is connected before driving the pin with an activating current, thereby simplifying the testing process.
Implementation Method 1
disconnecting the output pin from an amplifier and connecting the output pin to a current source, thereby charging a load circuit capacitance with a constant charge current
Data Source
Figure 1A
Figure 1B
Figure 2(a)~3(c)
AI summary
A system and method for testing capacitance of a load circuit connected to an output pin of a driving circuit In one embodiment, the method may comprise driving a voltage at the output pin to a first voltage; a predetermined current to the output pin; comparing the voltage at the output pin to a reference voltage; and when the voltage at the output pin matches the reference voltage, generating an estimate of capacitance present at the output pin based on a number of clock cycles occurring between an onset of a timed voltage change period and a time at which the voltage at the output pin matches the reference voltage.