Reset Synchronizer Circuit for Multi-Clock Domain Timing Safety
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Solution Overview
Problem
Integrated circuits with multiple clock domains face timing violations due to asynchronous clock signals, leading to erroneous operations when attempting to synchronize functional resets across these domains.
Innovation Solution
A reset synchronizer circuit comprising first, second, and third flip-flops, where the first flip-flop receives a functional reset signal and generates a logic low signal at the positive edge of the second clock signal, which is then synchronized by the second and third flip-flops to provide a logic low signal that resets the second chain of flip-flops, ensuring synchronization without timing violations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a functional reset signal is generated in one clock domain to reset flip-flops in another clock domain, then reset functionality is achieved across clock domains, but timing violations occur due to asynchronous clock signals
Solution Approach 1:
The patent introduces an intermediary synchronizer circuit comprising three flip-flops (FF1, FF2, FF3) that mediates between the first clock domain (CLK1) and second clock domain (CLK2). The functional reset signal from CLK1 domain passes through these synchronizer flip-flops clocked by CLK2, which absorb the asynchronous timing differences and produce a synchronized reset signal that is timing-safe for the second clock domain.
Solution Approach 2:
The synchronizer circuit performs preliminary synchronization of the reset signal before it is used to reset flip-flops in the second clock domain. By pre-processing the reset signal through multiple clocked stages (FF1, FF2, FF3), the circuit ensures that the reset assertion and deassertion occur at safe timing points relative to CLK2 edges, preventing timing violations in advance.
2Productivity
If asynchronous clock signals are used in different clock domains, then system flexibility and performance are improved, but timing violations and erroneous operations occur during cross-domain signal transfer
Solution Approach 1:
The three-stage synchronizer circuit acts as an intermediary that enables safe communication between asynchronous clock domains. Each flip-flop in the synchronizer chain is clocked by CLK2, creating a controlled interface that allows the high-performance asynchronous architecture to maintain operational correctness through proper timing synchronization.
Solution Approach 2:
The synchronizer circuit performs preliminary timing alignment of cross-domain signals before they enter the second clock domain logic. This pre-synchronization ensures that signals like functional reset assertions and deassertions occur at safe points in the CLK2 cycle, preventing metastability and timing violations while preserving the benefits of asynchronous clock operation.
3Device complexity
If a simple reset signal path is used between clock domains, then device complexity is reduced, but timing violations occur leading to erroneous operation
Solution Approach 1:
The reset synchronization function is segmented into three distinct flip-flop stages (FF1, FF2, FF3) rather than using a single direct connection. This segmentation distributes the timing synchronization task across multiple discrete elements, making the overall circuit more reliable while keeping each individual flip-flop simple and standard.
Solution Approach 2:
Instead of a simple direct reset path, the patent introduces intermediary synchronizer flip-flops that mediate the reset signal transfer. These intermediaries add minimal complexity (three standard flip-flops) but provide robust timing synchronization that prevents timing violations, making the added complexity worthwhile for achieving reliable operation.
Data Source
AI summary
A system for synchronizing a functional reset between first and second clock domains that operate on first and second clock signals, respectively. The system includes first, second and third synchronizer flip-flops that operate on the second clock signal. The first synchronizer flip-flop receives a functional reset signal generated by the first clock domain at its reset terminal and generates a low output signal. The low output signal causes the second synchronizer flip-flop and subsequently the third synchronizer flip-flop to generate low output signals at positive edges of the second clock signal. The low output signal generated by the third synchronizer flip-flop is used to reset the second clock domain.