Mixed-Vt Scan D Flip-Flop Layout for Hold-Slack Control
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Solution Overview
Problem
Existing flip-flop designs face challenges in avoiding hold-slack violations and data-racing problems while maintaining a compact footprint, often requiring additional transistors or compromising circuit functionality.
Innovation Solution
Implementing a mix of threshold voltages in flip-flop transistors, specifically using a combination of low, standard, and high threshold voltage transistors, without adding extra transistors or removing critical inverters, to manage setup-slack and hold-slack violations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional transistors are added to prevent hold-slack violations, then reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by assigning different threshold voltage characteristics to transistors in different circuit locations. Specifically, the first inverter uses a first threshold voltage transistor while the second inverter uses a second threshold voltage transistor, creating localized electrical property variations that prevent hold-slack violations without adding transistors throughout the entire circuit.
Solution Approach 2:
The patent changes the threshold voltage parameter of transistors based on their position in the flip-flop circuit. By selecting transistors with different threshold voltages (first threshold voltage for the first inverter, second threshold voltage for the second inverter), the patent modifies the electrical parameters to achieve proper timing margins and prevent hold-slack violations.
2Productivity
If transistor size is reduced to increase density, then productivity is improved, but manufacturing precision becomes more difficult
Solution Approach 1:
The patent implements local quality by creating distinct regions with different threshold voltage characteristics. Instead of uniformly scaling all transistors, the patent selectively applies different threshold voltage types to specific transistors based on their functional requirements, allowing density improvement while maintaining precise threshold voltage control where critical.
Solution Approach 2:
The patent changes the threshold voltage parameter selectively for different transistors in the circuit. By using transistors with different threshold voltage parameters (first threshold voltage vs. second threshold voltage) in different inverter stages, the patent achieves the desired timing characteristics without requiring uniform scaling, thereby maintaining manufacturing precision.
3Device complexity
If critical inverters are removed to reduce complexity, then device complexity is reduced, but reliability deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the threshold voltage characteristics of inverters based on their specific functional roles. The first inverter uses a first threshold voltage transistor while the second inverter uses a second threshold voltage transistor, creating localized property variations that maintain data-racing prevention capabilities without requiring additional inverters.
Solution Approach 2:
The patent changes the threshold voltage parameter of transistors in different inverter stages to achieve proper timing control. By selecting appropriate threshold voltage parameters for each inverter, the patent maintains the necessary timing margins to prevent data-racing issues while using exactly two inverters without adding extra stages.
Data Source
AI summary
A semiconductor device includes: a cell region including active regions in which components of transistors are formed that have Vt_low, Vt_std or Vt_high thresold voltages, the transistors being arranged to function as a scan-insertion D flip-flop (SDFQ) that includes a multiplexer and a D flip-flop (DFF); the DFF including a clock buffer, a primary latch and a secondary latch; the primary latch including a first sleepy inverter and a first non-sleepy (NS) inverter; the secondary latch including a second sleepy inverter and a second NS inverter; the clock buffer including third and fourth NS inverters; transistors which comprise at least one of the third NS inverter or the fourth NS inverter being Vt_low tranistors; transistors which comprise the first sleepy inverter are Vt_high transistors or transistors which comprise the second sleepy inverter are Vt_high transistors; and wherein transistors which comprise the multiplexer are Vt_std transistors.