Power-On Reset Circuit with Comparator Trust Verification
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Solution Overview
Problem
Generating a reliable power-on reset (POR) signal in integrated circuits is challenging, especially when the supply voltage has a slow or unpredictable rise, leading to potential system bugs due to unreliable comparator outputs at low bias currents.
Innovation Solution
A power-on reset circuitry comprising a comparator, a trust unit, and a decision unit, where the trust unit forms a replica of the comparator's output part to provide a trust signal indicating the reliability of the POR trigger signal, ensuring accurate generation of the POR signal based on the supply voltage reaching a target level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a comparator is used to generate the POR signal by comparing scaled supply voltage with reference voltage, then the POR signal can be generated based on voltage threshold detection, but the comparator output may be unreliable when bias current is low at start-up
Solution Approach 1:
The patent creates a replica of the comparator's first output part (including the first node, first component, and second component) as a second output part in the trust unit. This copy allows verification of whether the comparator output is reliable by checking if the unbalanced input causes unexpected voltage changes at the replicated node, thereby detecting unreliable comparator states without affecting the original voltage threshold detection function.
Solution Approach 2:
The trust unit acts as an intermediary between the comparator and the decision unit. It receives the POR trigger signal and additional input, processes them through the replicated output circuitry, and generates a trust signal that mediates whether the comparator output should be accepted. This intermediary layer filters out unreliable comparator outputs while preserving valid ones.
2Loss of time
If the POR signal is provided before the supply voltage has settled, then the system startup time is reduced, but the system exhibits buggy behavior due to unreliable operation
Solution Approach 1:
The trust unit provides feedback about the reliability of the comparator output to the decision unit. By monitoring the voltage at the first node and comparing it with the unbalanced input condition, the trust unit generates a trust signal that feedbacks whether the POR trigger signal is reliable. This feedback mechanism ensures the POR signal is only generated when both voltage threshold is met and comparator output is verified reliable, preventing buggy behavior while minimizing unnecessary delays.
3Reliability
If the bias current of the comparator is increased to improve output reliability, then the comparator output becomes more reliable, but the power consumption of the system increases
Solution Approach 1:
Instead of increasing bias current to improve reliability, the patent copies the output circuitry to create a verification path. The trust unit replicates the first output part and uses it to verify comparator reliability under normal bias current conditions. This copying approach achieves reliability verification without requiring increased power consumption for higher bias current.
Solution Approach 2:
The trust unit uses a disposable verification approach where the replicated circuit components are used temporarily only for reliability verification during startup. Once the POR signal is generated and the system is reset, the verification function is no longer needed, allowing the system to operate efficiently without the continuous overhead of high bias current.
Data Source
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AI summary
A power-on reset, POR, circuitry (100; 200) comprises: a comparator (110; 210) configured to output a POR trigger signal in dependence of a relation between a supply voltage and a target voltage level, wherein the comparator (110; 210) comprises a first output part (118; 218) configured to receive a balanced input; a trust unit (140; 240) comprising a second output part (144; 244) forming a replica of the first output part (118; 218) and configured to receive an unbalanced input, wherein the comparator (110; 210) and the trust unit (140; 240) are arranged in a common integrated circuit and wherein the trust unit (140; 240) is configured to output a trust signal indicating whether the POR trigger signal is trustable; and a decision unit (130; 230) configured to output a POR signal in dependence of the POR trigger signal and the trust signal.