Leaf-Level Programmable Clock Delays for Low-Skew Phase Shifting
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Solution Overview
Problem
Conventional clock distribution networks in programmable integrated circuits face challenges in generating multiple phase-shifted clock signals, as the phase shift introduced by phase-locked loops (PLLs) is affected by random variations in the global clock network, leading to increased jitter and skew, especially over longer distances.
Innovation Solution
The method involves generating a base clock signal and applying programmable delays at the leaf level in the clock distribution network, allowing for the generation of multiple phase-shifted clock signals, reducing unwanted skew and power consumption by moving the clock generation closer to the source and destination flip-flops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If phase-locked loops (PLLs) are used to generate phase-shifted clock signals in conventional clock distribution networks, then multiple clock phases can be generated, but jitter and skew increase especially over longer distances due to random variations in the global clock network
Solution Approach 1:
The invention segments the clock distribution network into multiple regional clock trees, each serving a specific region of the FPGA. Instead of using a single global PLL to generate all clock phases, each regional clock tree has its own local PLL that generates clock phases independently for its region. This segmentation isolates the random variations in different regions, preventing them from affecting the entire clock network, thereby reducing jitter and skew while maintaining the ability to generate multiple clock phases.
Solution Approach 2:
The invention implements local quality by allowing each regional clock tree to have customized clock generation characteristics tailored to its specific region's requirements. Each local PLL can be independently configured with different phase shift values and timing parameters optimized for its regional needs. This local customization enables precise control over clock phase and timing in each region without being constrained by global variations, thereby improving reliability while maintaining adaptability.
2Device complexity
If a single global clock network is used to distribute clock signals throughout the FPGA, then clock distribution is simplified, but skew and timing variations increase over longer distances
Solution Approach 1:
The clock distribution network is segmented into multiple regional clock trees, each responsible for a specific region of the FPGA. This segmentation reduces the distance that clock signals must travel within each regional tree, thereby minimizing skew and timing variations. While this increases the number of PLL components, it maintains timing precision by limiting the impact of random variations to local regions only.
Solution Approach 2:
The invention introduces a spatial dimension to clock distribution by organizing the FPGA into multiple regions with dedicated clock trees. Instead of a single hierarchical level, the system uses a two-dimensional structure where each region has its own clock generation resources. This dimensional change allows the system to maintain simple local distribution while achieving global coverage, balancing device complexity with timing precision.
3Adaptability or versatility
If multiple phase-shifted clock signals are generated using conventional PLL-based methods, then clock phases are available for various operations, but power consumption increases
Solution Approach 1:
The invention applies local quality by enabling phase-shifted clock signal generation only in the regions where they are actually needed. Each local PLL can be independently enabled or disabled based on the specific requirements of its region. This selective activation allows the system to maintain adaptability by providing phase-shifted clocks where required while reducing overall power consumption by keeping unused local PLLs in a low-power or disabled state, rather than running a single global PLL at full power to serve all regions.
Data Source
AI summary
Methods and apparatus for generating multiple phase-shifted clock signals from a base clock signal using programmable delays at the leaf level in a clock distribution network are described. One example method for generating and distributing multiple phase-shifted clock signals in a programmable integrated circuit (IC) generally includes generating a base clock signal, routing the base clock signal through a clock distribution network in the programmable IC to a leaf node, and applying one or more programmable delays to the base clock signal received from the leaf node to generate the multiple phase-shifted clock signals.