Feedback Comparator Circuit for Low-Power Over-Voltage Detection
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Solution Overview
Problem
Traditional comparator circuits are unreliable for comparing supply voltages that are equal to or higher than the comparator's supply voltage, and they consume excessive power, making them unsuitable for detecting supply voltage incompatibilities and tampering events in System on Chips (SoCs).
Innovation Solution
A low-power coarse comparator circuit with a feedback mechanism that automatically disables the comparator when the output switches, using P-channel and N-channel transistors to compare DC voltage levels and detect over-voltage conditions, consuming negligible DC current and capable of remaining always on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional comparator is used to compare supply voltages, then voltage comparison function is provided, but power consumption is excessive and reliability is poor when voltages are close to or above supply voltage
Solution Approach 1:
The comparator circuit dynamically changes its operating state based on the comparison result. When a voltage mismatch is detected, the circuit transitions from an active comparison state to a disabled state, where power consumption becomes negligible. This dynamic state change allows the comparator to maintain high reliability during detection while consuming minimal power during normal operation.
Solution Approach 2:
The circuit employs a feedback mechanism where the output of the comparator is fed back to control the enable signal. When the comparator detects that voltages are equal (or within acceptable range), the feedback signal disables the comparator, preventing excessive power consumption. This feedback loop ensures the comparator only remains active when voltage differences exist, resolving the contradiction between reliability and power consumption.
2Reliability
If a traditional comparator operates continuously to detect voltage variations, then voltage tampering detection is achieved, but power consumption increases
Solution Approach 1:
Instead of continuous operation, the comparator is enabled only periodically when voltage differences are detected. The circuit uses an enable signal that activates the comparator only during relevant comparison periods, allowing it to detect voltage tampering events while consuming negligible DC current during idle periods when voltages are stable and equal.
3Extent of automation
If a comparator is designed to always be on for continuous monitoring, then voltage security monitoring is improved, but power consumption becomes problematic
Solution Approach 1:
The comparator circuit automatically manages its own power consumption by using its output signal to control its enable state. When voltages are equal and no tampering is detected, the circuit self-disables to eliminate standby power consumption. This self-service mechanism maintains continuous monitoring capability while ensuring negligible power consumption during normal operation, resolving the contradiction between automation and energy use.
Data Source
AI summary
A comparator circuit includes a first transistor have a control electrode coupled to a first input voltage, a first current electrode coupled to a second input voltage, and a second current electrode coupled to a first circuit node. The circuit also includes a first inverter coupled to a first voltage supply terminal and having a first input coupled to the first circuit node and an output, a second transistor having a control electrode coupled to the output of the first inverter, and an active resistive element coupled in series between the first circuit node and a first current electrode of the second transistor.