Shielded Single-Ended Clock Routing for Low Crosstalk
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Solution Overview
Problem
Crosstalk between clock lines in high-speed clock distribution circuits introduces undesirable jitter, limiting the critical clock distribution specification and requiring increased power consumption and chip area with differential clock signals.
Innovation Solution
A shield structure, comprising a shield wall and/or shield cage, is used to reduce crosstalk in single-ended clock distribution circuits, allowing for increased distribution span within specified jitter limits and reducing power and area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If differential clock signals are used to mitigate crosstalk, then crosstalk and jitter are reduced, but power consumption increases and chip area increases
Solution Approach 1:
A shield structure comprising a first layer, second layer, and third layer is introduced as an intermediary between adjacent clock lines. The shield is connected to AC ground through via holes, creating a reference potential that blocks electromagnetic coupling between clock lines. This mediator structure reduces crosstalk without requiring differential signaling, thus avoiding the power and area penalties of differential pairs.
Solution Approach 2:
The patent changes the electromagnetic environment parameters by introducing grounded shield layers at specific positions between clock lines. By modifying the electrical parameters (grounding the shield at via holes) and spatial parameters (positioning shields at critical coupling points), the crosstalk is reduced while maintaining single-ended signaling efficiency.
2Reliability
If differential clock signals are used to mitigate crosstalk, then crosstalk and jitter are reduced, but chip area increases
Solution Approach 1:
The shield structure serves as a compact intermediary that fits within the existing single-ended clock line routing space. By placing thin grounded layers between adjacent clock lines and connecting them via via holes to AC ground, the shield provides effective crosstalk cancellation without requiring the additional space needed for differential pair routing.
Solution Approach 2:
The solution moves from a planar routing problem to a three-dimensional shielding approach. By introducing vertical via holes connecting the shield layers to AC ground, the patent utilizes the vertical dimension to create effective electromagnetic shielding within the limited lateral space available on the chip, avoiding the area expansion required by differential signaling.
3Length of stationary object
If clock lines are routed alongside each other for long distance, then distribution span is increased, but crosstalk and jitter increase
Solution Approach 1:
The long clock distribution path is segmented into multiple sections by strategically placing shield structures at intervals along the routing. Each shield segment independently suppresses crosstalk in its local region, allowing the overall distribution span to be extended while maintaining jitter specifications through cumulative protection along the entire path.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The shield structure doubles the clock distribution span while meeting jitter requirements, achieving power and area savings, and can be adapted for various clock line configurations and semiconductor processes.
Implementation Method 1
a shield structure, for example either one or both of a shield wall and shield cage
Data Source
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AI summary
An integrated circuit is described. The integrated circuit includes a first layer, a first clock line for carrying a first clock signal, and a second clock line for carrying a second clock signal. The second clock line runs alongside the first clock line for a distance. The integrated circuit includes a shield structure for shielding the clock line from at least one of crosstalk and other interference. The shield structure includes a shield wall extending from the first layer. The shield wall runs between the first and second clock lines for at least a portion of the distance. The shield structure may also include a shield cage extending from the first layer and surrounding the first and second clock lines for at least a portion of the distance. The shield cage has a plurality of openings. At least one of the shield cage and shield wall may be connected to the ground of an AC power supply.