Multi-Bit Flip-Flop Scan Chain Layout for Lower Transistor Count
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Solution Overview
Problem
Existing multi-bit flip-flop registers require a large number of transistors due to cascading bits and shared clock/scan generation logic, leading to increased integrated circuit area and manufacturing costs.
Innovation Solution
The internal scan logic in a multi-bit flip-flop register is connected in a serial scan chain, reusing logic between slave latches on bit n and master latches on bit n+1, reducing the number of transistors needed and consequently the integrated circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If discrete independent flip-flops are used, then reliability and independence of each bit is improved, but integrated circuit area and manufacturing cost increase
Solution Approach 1:
Multiple flip-flops are merged into a single multi-bit flip-flop structure where individual bits are connected in a serial scan chain. The master latches and slave latches are shared across multiple bits, reducing the total transistor count while maintaining functional independence of each bit through selective enabling.
Solution Approach 2:
The shared master latches and slave latches serve multiple functions: they can operate independently as discrete flip-flops for normal data storage, or they can be connected in a serial scan chain for testing and initialization. The scan enable signal controls whether the structure operates in normal mode or scan mode, providing universal functionality.
2Ease of manufacture
If common clock/scan generation logic is shared, then manufacturing cost is reduced, but device complexity increases
Solution Approach 1:
The logic structure is made dynamic through the scan enable signal, which controls the operation mode. When scan enable is inactive, the flip-flop operates in normal mode with independent bit functionality. When scan enable is active, the bits connect in a serial scan chain, dynamically reconfiguring the logic path without requiring separate hardware for each mode.
3Reliability
If more transistors are used per bit, then bit independence and reliability are improved, but area efficiency decreases
Solution Approach 1:
Adjacent flip-flops share common master latches and slave latches, merging redundant logic elements into a single shared structure. This reduces the total number of transistors required while maintaining the functional independence of each bit through the scan chain connection and selective enabling mechanism.
Data Source
AI summary
The invention is an intelligent connection of the internal scan logic in a multi-bit flip-flop register. Individual bits in this register are connected in a serial scan chain. In this invention the serial chain is connection reuses logic between slave latches on bit n and master latches on bit n+1. This reuse reduces the number of transistors required to implement the multi-bit register. This reduction in the number of required transistors enables a consequent reduction in integrated circuit area required, thereby reducing manufacturing cost. Alternatively, the area saved using this invention may be used for other purposes. This could increase the value of the corresponding integrated circuit without increasing manufacturing costs.