Selectable Reset Threshold Circuit for Low-Voltage IC Testing
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Solution Overview
Problem
Existing reset circuits in integrated circuit packages prevent low voltage testing by disabling the digital circuit under test before the power supply voltage reaches the reset threshold, making it difficult to determine if the circuit operates properly at voltages below the reset threshold.
Innovation Solution
A selectable threshold reset circuit that allows the reduction of the reset threshold voltage, enabling the circuit to operate and test at lower voltages without disabling the reset signal, by selectively changing the voltage level at which the RESET signal is outputted, allowing for proper functionality assessment during low voltage testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reset circuit outputs the RESET signal at the normal reset threshold voltage, then the digital circuit is protected from operating at unsafe voltages, but low voltage testing cannot be performed
Solution Approach 1:
The reset threshold voltage is made dynamically selectable between a normal threshold (for reliable operation) and a test threshold (for low voltage testing). The circuit transitions from a fixed threshold design to a dynamic one where the threshold can be adjusted based on whether testing or normal operation is required, resolving the contradiction between safety protection and testing capability.
Solution Approach 2:
The key parameter changed is the reset threshold voltage level. By providing multiple threshold options (normal threshold and test threshold) and allowing selection between them, the circuit can adapt to different operational requirements. This parameter change enables both reliable operation at normal thresholds and low voltage testing at reduced thresholds.
2Adaptability or versatility
If the power supply voltage is reduced below the reset threshold to test the digital circuit, then low voltage operation can be tested, but the reset circuit will disable the digital circuit before the test voltage is reached
Solution Approach 1:
The reset threshold is dynamically adjusted to match the test conditions. When testing at reduced voltages, the circuit selects a corresponding lower test threshold, allowing the digital circuit to operate and be tested at the reduced voltage without being prematurely disabled by the reset signal.
Solution Approach 2:
Before performing low voltage testing, the reset threshold is preliminarily adjusted to the test threshold level. This preliminary action ensures that when the power supply voltage is reduced during testing, the reset circuit will not interfere with the test by disabling the digital circuit at the normal higher threshold voltage.
3Adaptability or versatility
If a test mode is implemented to inhibit RESET signal generation, then low voltage testing becomes possible, but the integrated circuit may inadvertently enter test mode and it is difficult to determine if normal operation has been restored
Solution Approach 1:
The selectable threshold mechanism serves dual purposes: it enables low voltage testing when the test threshold is selected, and it ensures reliable normal operation when the normal threshold is selected. This multi-functionality eliminates the need for a separate test mode that could be inadvertently activated, as the same circuit mechanism handles both testing and normal operation.
Solution Approach 2:
The selectable threshold circuit acts as an intermediary between the power supply voltage monitoring and the reset signal generation. By providing controlled access to different threshold levels through this intermediary mechanism, the system avoids the problems of inadvertent test mode activation while still enabling low voltage testing when properly configured.
Data Source
AI summary
A low voltage testing circuit (125), system (100 and 200), and method for performing low-voltage testing of a circuit (127) in an integrated circuit package (104 and 204) include a selectable threshold reset circuit (125) that includes a voltage-divider ladder (320) that produces a voltage that is a fraction of a power supply voltage, a comparator (310) that compares the fraction with a reference voltage, a switch (350) that controls topology of the voltage-divider ladder thereby changing a value of the fraction, the switch controlled by a signal from a production tester (102 and 202), the signal causing a reset threshold of the selectable threshold reset circuit to be reduced below a normal reset threshold to allow testing of the circuit at a power supply voltage below the normal reset threshold.