Waveform Edge Timing Variation Under Simultaneous Switching Noise
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Solution Overview
Problem
Current methods for reducing simultaneous switching noise (SSN) in integrated circuits and IC packages are either costly or require expertise, as they either sacrifice I/O buffer densities or increase costs, and existing SSN analysis tools are cumbersome and time-consuming, making it difficult for designers to perform comprehensive SSN analysis within a short design cycle.
Innovation Solution
A method and system for determining timing variations in transitioning waveforms under SSN conditions by calculating amplitude values related to inductive crosstalk and power distribution network noise, adjusting these values with pre-calculated constants derived from physical measurements, and combining them to determine the impact of additional aggressor pins, allowing for accurate and efficient SSN analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If mutual inductive coupling is minimized by increasing the ratio of ground pins to I/O buffers, then SSN is reduced, but I/O buffer density is sacrificed
Solution Approach 1:
The patent changes the parameters of the PDN by adding on-die capacitance and on-package decoupling capacitors, and by modifying the impedance profile through controlled impedance routing. These parameter changes reduce SSN without requiring changes to the I/O buffer layout, thus maintaining buffer density while improving signal integrity
Solution Approach 2:
The patent introduces decoupling capacitors as intermediary elements between the power distribution network and the switching buffers. These capacitors act as local energy reservoirs that compensate for voltage fluctuations caused by simultaneous switching, thereby reducing SSN without affecting the physical arrangement of I/O buffers
2Object-affected harmful factors
If PDN performance is improved by increasing on-die capacitance and adding on-package decoupling capacitors, then SSN is reduced, but cost increases
Solution Approach 1:
The patent performs preliminary SSN analysis and simulation during the design phase to identify critical switching scenarios and optimize the PDN configuration before fabrication. This allows for cost-effective selection of decoupling capacitor values and placements, avoiding over-engineering and unnecessary cost increases
Solution Approach 2:
The patent optimizes the impedance profile of the PDN through careful selection of trace widths, spacing, and layer configurations. By achieving acceptable SSN reduction through parameter optimization rather than adding more capacitors, the manufacturing cost is controlled while still improving PDN performance
3Measurement precision
If system-level SPICE-like models are used to anticipate SSN, then accurate predictions are obtained, but time-consuming simulations are required
Solution Approach 1:
The patent segments the SSN analysis into distinct components: individual buffer switching characteristics, mutual inductive coupling effects, and PDN impedance responses. Each segment is analyzed separately using simplified models, and the results are combined to obtain the overall SSN prediction. This segmentation enables faster computation compared to full system-level SPICE simulation while maintaining accuracy
Solution Approach 2:
The patent creates simplified equivalent circuit models that copy the essential characteristics of the complex PDN and buffer interactions. These equivalent models use lumped elements representing the distributed PDN structure, enabling rapid SSN analysis without requiring detailed knowledge of the entire system while still providing accurate predictions
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
This approach provides an accurate and computationally efficient method for predicting timing variations due to SSN, enabling designers to optimize I/O buffer assignments and meet design constraints without additional costs, improving signal and power integrity while reducing design cycle time.
Implementation Method 1
the mutual inductive coupling among switching input/output (I/O) buffers
Implementation Method 2
Simultaneous switching noise (SSN) in an integrated circuit (IC) and the IC package may be attributed to two primary factors: the mutual inductive coupling among switching input/output (I/O) buffers and the impedance profile of a power distribution network (PDN)
Data Source
AI summary
A computer implemented method for determining a timing variation for an edge of a waveform under simultaneous switching noise (SSN) conditions is provided. The method includes characterizing an impact of mutual inductive relationships on a pin while the pin is at a quiet state and characterizing a signal edge applied to the pin. The signal edge can be characterized by the slew rate in one embodiment. A voltage change related to a curve characterizing the impact of mutual inductive relationships is identified and the voltage change is applied to a curve characterizing an impact of SSN on the signal edge. The method includes calculating a timing variation correlated to the voltage change applied to the curve characterizing the impact of SSN on the signal edge and presenting the calculated timing variation.