Scan Chain Reset Layout Using Inverted Asynchronous States
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Solution Overview
Problem
The use of set/reset flip-flops in scan chains for universal asynchronous reset (UAR) methodologies results in larger flip-flops, affecting the area, power consumption, and speed of operation in systems on chip (SoC), necessitating a more efficient approach using non-set/non-reset flip-flops.
Innovation Solution
The implementation of an asynchronous reset scheme that differentiates between flip-flops designed to store a 0 or a 1 by using non-set/non-reset flip-flops for resetting, allowing for clocking the desired state into flip-flops and utilizing built-in set/reset circuitry for inverse states, reducing the need for set/reset pins and minimizing area and power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If set/reset flip-flops are used in scan chains for universal asynchronous reset methodologies, then asynchronous reset functionality is achieved, but the area, power consumption, and speed of operation are adversely affected
Solution Approach 1:
The scan chain is segmented into two separate chains: a first scan chain containing flip-flops to be reset to 0, and a second scan chain containing flip-flops to be reset to 1. This segmentation allows each chain to be optimized independently, with the first chain using simple reset logic and the second chain using inverted reset logic, thereby reducing the overall area requirement compared to using set/reset flip-flops in all positions
Solution Approach 2:
The second scan chain uses an inverted reset approach where the reset value is logically inverted (reset to 1 instead of 0) and the scan input is inverted. This inversion technique allows the use of non-set/non-reset flip-flops to achieve the same functional effect as set/reset flip-flops, reducing area while maintaining asynchronous reset functionality
2Reliability
If set/reset flip-flops are used in scan chains, then asynchronous reset capability is provided, but power consumption increases
Solution Approach 1:
The set/reset functionality is extracted from individual flip-flops and implemented at the scan chain level through separate scan chains with different reset configurations. This extraction eliminates the need for set/reset circuitry within each flip-flop, reducing power consumption while maintaining the ability to perform asynchronous resets across the entire scan chain
Solution Approach 2:
The reset parameter (reset value) is changed from the conventional 0 to 1 for the second scan chain, and the scan input parameter is inverted. This parameter change allows the use of simpler non-set/non-reset flip-flops that consume less power, while the system still achieves comprehensive asynchronous reset coverage through the dual-chain architecture
3Reliability
If set/reset flip-flops are used in scan chains, then universal asynchronous reset is achieved, but operational speed decreases
Solution Approach 1:
By segmenting the scan chain into two separate chains with different reset configurations, each chain can be optimized for speed. The first chain uses straightforward reset-to-0 logic while the second chain uses inverted reset-to-1 logic, eliminating the need for complex set/reset circuitry that would slow down operation, while still achieving universal asynchronous reset coverage
Data Source
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AI summary
A first apparatus (300) includes at least one scan chain. Each of the at least one scan chain includes scan cells coupled together. Each scan cell in the at least one scan chain includes a first type of scan cell (302, 304, 308, 312, 314) when a reset state of the scan cell is a first state, and a second type of scan cell (308, 310) when the reset state of the scan cell is a second state. One or more scan chains of the at least one scan chain includes at least one of the first type of scan cell and at least one of the second type of scan cell. A second apparatus (500) includes first (502) and second (504) sets of scan chains including flip-flops without both set and reset functionality. Each of the flip-flops in the first and second sets of scan chains has a reset state of a first state and a second state, respectively.