Arbiter Circuit Metastability Filter and Kicker Mechanism
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Solution Overview
Problem
Conventional asynchronous arbiter circuits face metastability conditions due to simultaneously asserted inputs, leading to indefinite resolution times and uncertainty in operation, especially at lower power supply voltages and varying temperatures.
Innovation Solution
The proposed arbiter circuit includes a latch circuit, a metastability filter, and a kicker section to distinguish between no match and metastable states, using a filter section to drive outputs to predetermined levels and a kicker section to force the latch into a stable state, thereby resolving potential metastable states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional asynchronous arbiter circuits are used, then the circuit can resolve conflicts between two signals, but metastability conditions occur when two inputs are simultaneously asserted, leading to indefinite resolution times and uncertainty in operation
Solution Approach 1:
The filter circuit proactively detects potential metastability conditions by monitoring the voltage level at the latch input before the latch actually enters a metastable state. When a potential metastability condition is detected (voltage within threshold window), the filter circuit preemptively activates the kicker circuit to force the latch into a stable state, preventing the metastability from occurring in the first place and ensuring timely resolution.
Solution Approach 2:
The filter circuit continuously monitors the voltage level at the latch input and uses this feedback information to determine when to activate the kicker circuit. The feedback mechanism compares the monitored voltage against predefined thresholds to detect metastability conditions and triggers appropriate corrective action, ensuring the latch remains in a stable state and resolution time is maintained.
2Reliability
If gate sizes are sized to skew trip point in conventional latches, then metastability may be reduced, but operation cannot be ensured over all anticipated operating conditions including power supply voltages, temperatures, and manufacturing variations
Solution Approach 1:
Instead of relying on fixed gate sizing, the invention dynamically adjusts the trip point parameter through the filter circuit's voltage monitoring and comparison mechanism. The filter circuit adapts to different operating conditions by detecting when the latch input voltage falls within the metastability threshold window, regardless of variations in power supply voltage, temperature, or manufacturing processes, and activates the kicker circuit accordingly to maintain stable operation.
Solution Approach 2:
The filter circuit acts as an intermediary between the latch input and the latch itself, monitoring the voltage level and mediating by activating the kicker circuit when potential metastability is detected. This intermediary mechanism decouples the latch from direct sensitivity to operating condition variations, allowing the system to maintain reliable operation across all anticipated conditions without requiring precise gate sizing.
3Reliability
If filter circuits with always on PFETs are used to force outputs to predetermined levels, then metastable states are eliminated, but arbiter outputs are the same in no address match state and metastable state
Solution Approach 1:
The invention extracts the metastability detection and correction function into a separate filter circuit with kicker circuit, distinct from the main latch output logic. The filter circuit monitors latch input voltage and activates the kicker only when potential metastability is detected, leaving the normal arbiter output logic unchanged. This separation allows the system to eliminate metastable states while preserving the ability to distinguish between no match and match states through the normal output logic paths.
Solution Approach 2:
The filter circuit serves as an intermediary that detects potential metastability conditions and activates the kicker circuit only when needed, rather than continuously forcing outputs to predetermined levels. This intermediary approach eliminates metastable states while allowing the normal arbiter output logic to maintain proper state distinction information for no match versus match conditions.
Data Source
AI summary
An arbiter circuit (100) can include a latch circuit (102) that latches competing input signals (MATCH1 and MATCH2) to generate signals on latch output (110-0 and 110-1). A filter section (104) can prevent metastable states of latch output signals from propagating through to output signals (BUSY2 and BUSY1). In addition, filter section (104) can generate output signals (BUSY2 and BUSY1) having one set of values when both inputs are inactive, and a second set of values when latch (102) is in the metastable state.