Positive Feedback LOS Circuit for Fast USB Signal Detection
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Solution Overview
Problem
Existing loss of signal (LOS) detectors in USB and eUSB2 systems have slow response times, often requiring signal filtering that can lead to false detection triggers and increased circuit size, making them incompatible with fast response and minimum propagation delay requirements.
Innovation Solution
A multi-stage switchable positive feedback differential glitch suppressor circuit that uses comparators and positive feedback circuits to determine the magnitude of differential signal lines, eliminating the need for signal filtering in the output path and reducing non-overlapping regions to achieve fast LOS detection within 2 unit intervals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If signal filtering is applied in existing LOS detectors, then false detection triggers are reduced, but response time increases and circuit size increases
Solution Approach 1:
The patent implements a positive feedback mechanism where the output of the differential comparator is fed back to its input through a feedback network. This positive feedback creates a latch effect that maintains the output state once a threshold is crossed, eliminating the need for external signal filtering while ensuring stable detection and preventing false triggers.
Solution Approach 2:
The patent employs dynamic switching of feedback paths based on the detection state. When signal levels indicate a loss condition, the feedback network dynamically changes configuration to maintain the detected state, allowing the circuit to adapt its behavior based on real-time signal conditions without requiring slow filtering operations.
2Reliability
If signal filtering is applied in existing LOS detectors, then false detection triggers are reduced, but circuit size increases
Solution Approach 1:
The patent combines the filtering function with the comparison and detection functions into a single integrated circuit block. The feedback network performs both signal level comparison and false trigger prevention simultaneously, eliminating the need for separate filtering components and reducing overall circuit complexity.
Solution Approach 2:
The differential comparator circuit serves its own filtering needs through the positive feedback mechanism. The feedback network automatically suppresses false triggers by maintaining the output state once a valid detection is made, making the circuit self-sufficient without requiring external filtering components.
3Speed
If fast response LOS detection is implemented, then detection speed improves, but susceptibility to false triggers increases
Solution Approach 1:
The patent prepares the feedback network in advance to immediately latch the output state when a threshold crossing occurs. This preliminary configuration of the feedback path ensures that once a valid loss condition is detected, the circuit rapidly stabilizes to the correct state without oscillation or false transitions, achieving both speed and reliability.
Data Source
AI summary
Aspects of the disclosure provide for a circuit. In some examples, the circuit includes a first inverter coupled between first and second nodes, a second inverter coupled between third and fourth nodes, and a first logic circuit having a first input coupled to the second node, a second input coupled to the fourth node, and an output, a first positive feedback circuit coupled between the first and third nodes and having a control input. The first positive feedback circuit comprises a first switch coupled between the first and fifth nodes and having a control input, a second switch coupled between the third and sixth nodes and having a control input, a third inverter having an input coupled to the sixth node and an output coupled to the fifth node, and a fourth inverter having an input coupled to the fifth node and an output coupled to the sixth node.