Two-Stage NAND/NOR Register for Metastability-Resistant Latching
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Solution Overview
Problem
Sense amplifier-based registers are prone to metastable conditions and device mismatches, leading to erroneous operations due to manufacturing variations and sensitivity to power supply noise, which affects the accuracy of data capture.
Innovation Solution
A register design comprising a first stage and a second stage with feedback signals to block further propagation of the input signal, ensuring monotonic output signals by using cross-coupled NAND and NOR gates to stabilize output values during clock transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sense amplifier-based register uses cross-coupled transistors for data latching, then data capture capability is improved, but metastable conditions occur during clock transitions causing erroneous operations
Solution Approach 1:
The register is divided into two separate stages: a first sense amplifier stage for data capture and a second latch stage for stable storage. This segmentation isolates the metastable condition generation to the first stage while the second stage provides stable output, resolving the contradiction between data capture capability and operational reliability.
Solution Approach 2:
A second latch stage acts as an intermediary between the sense amplifier and the output. This intermediate stage buffers the metastable transitions from the first stage and provides clean, stable output signals, eliminating erroneous operations while preserving data capture accuracy.
2Reliability
If additional transistors are added to prevent metastable conditions, then operation reliability is improved, but device complexity increases
Solution Approach 1:
Instead of adding numerous transistors to a single stage, the solution segments the register into two functional stages with a defined interface. This achieves reliability improvement through architectural division rather than component proliferation, maintaining reasonable device complexity.
3Speed
If sense amplifier register is designed for fast clock transitions, then speed is improved, but sensitivity to power supply noise increases
Solution Approach 1:
The two-stage architecture separates the high-speed data capture function from the stable output function. The first stage can operate with fast clock transitions for speed, while the second stage provides noise immunity, resolving the contradiction between speed and noise sensitivity.
Solution Approach 2:
The second latch stage serves as a protective buffer that shields the output from power supply noise before it can affect the final output. This beforehand cushioning allows the first stage to operate at high speed without compromising noise immunity.
Data Source
AI summary
A register receives an input signal and provides output signals that represent true complementary logic values of the input signal. One implementation of the register includes: a first stage circuit and a second stage circuit. After the output signals are derived, the second stage circuit provides feedback signals to block further propagation of the logic value of the input signal from the first stage circuit to the second stage circuit.