Daisy-Chained Delay Cell Layout for Hold-Time and LDE Control
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Solution Overview
Problem
Existing semiconductor designs face challenges in managing layout-dependent effects (LDEs) and hold-time violations due to increased transistor density, leading to inefficiencies in flip-flop operations and potential signal misinterpretation.
Innovation Solution
A semiconductor device design that includes a delay arrangement with daisy-chained delay cells, utilizing float-resistant inverters and dummy transistors to minimize layout-dependent effects while optimizing hold-time, reducing the footprint, and ensuring reliable signal propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If transistor density is increased to reduce component sizes and tighten spacing, then IC size is reduced, but layout-dependent effects and hold-time violations increase
Solution Approach 1:
The flip-flop circuit is segmented into distinct functional blocks: delay cells (with float-resistant inverters) placed between adjacent flip-flops to provide localized delay control, and dummy transistor groups strategically positioned at edges and corners to compensate for layout-dependent effects in specific regions. This segmentation allows independent optimization of each component to address the hold-time and LDE issues arising from high density.
Solution Approach 2:
Different regions of the circuit receive different treatments: float-resistant inverters are placed in critical delay paths between flip-flops to locally extend hold-time, while dummy transistors are selectively positioned at edges and corners where LDEs are most severe. This local quality approach ensures that each area receives the specific compensation it needs without unnecessarily increasing overall circuit complexity.
2Reliability
If dummy transistors are added to mitigate layout-dependent effects, then LDEs are reduced, but device footprint increases
Solution Approach 1:
The dummy transistor groups are merged with the existing circuit layout structure, positioned at edges and corners where they serve dual purposes: compensating for LDEs in critical regions while utilizing otherwise empty space. The float-resistant inverters are merged into the signal path between flip-flops, providing delay compensation without requiring separate dedicated structures. This merging minimizes the additional footprint while achieving LDE mitigation.
3Reliability
If float-resistant inverters are used to extend hold-time, then hold-time violations are prevented, but device complexity increases
Solution Approach 1:
The float-resistant inverters provide dynamic delay adjustment capability, allowing the circuit to adapt to varying process, voltage, and temperature conditions. The extended hold-time is achieved through the inherent floating node behavior that naturally adjusts the delay characteristic, rather than through complex static circuit structures. This dynamic approach prevents hold-time violations without requiring overly complex circuit designs.
Data Source
AI summary
A method of forming a semiconductor device includes forming a first row of transistors extending in a first direction and including dummy transistors and active transistors. The first row includes, in a sequence from a first end to a second end, at least a first dummy group, a first delay cell, a second delay cell, and a second dummy group. The first dummy group is formed of one or more dummy transistors. The second dummy group is formed of one or more dummy transistors. The first delay cell is formed of active transistors configured as a basic inverter and a float-resistant inverter. The second delay cell is formed of active transistors configured as at least one inverter. The first row is free of dummy transistors between the first delay cell and the second delay cell.