Printed Circuit Board Impedance Matching for Signal Ringing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In high-density memory systems using DDR3-SDRAM, the long branched wiring between memory devices and the motherboard leads to significant signal attenuation and reflection, causing waveform ringing issues that can disrupt signal input voltage conditions, particularly in address/command signals.
Innovation Solution
The printed circuit board design incorporates a trunk wiring with strategically divided impedance sections, where the characteristic impedance of the first wiring portion is set to be equal or lower than the third wiring portion, and the second wiring portion has a higher impedance than the first, to manage signal reflections and attenuations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the branched wiring length is reduced by situating vias adjacent to mounting pads, then signal attenuation and reflection are reduced, but vias cannot be disposed between mounting pads in high-density configurations, forcing vias to the outer side and lengthening the branched wiring
Solution Approach 1:
The patent changes the characteristic impedance parameter of the trunk wiring to resolve the contradiction. By setting the characteristic impedance to a specific value (e.g., 50Ω or higher), the patent achieves proper signal matching that reduces reflection and attenuation, allowing the use of longer branched wiring in high-density configurations without compromising signal quality.
2Quantity of substance
If the branched wiring is made longer to accommodate high-density mounting pad arrangements, then more mounting pads can be connected, but signal attenuation and reflection increase, causing waveform ringing that disrupts input voltage conditions
Solution Approach 1:
The patent applies parameter changes by optimizing the characteristic impedance of the trunk wiring. This impedance parameter adjustment compensates for the increased wiring length, reducing signal attenuation and reflection to levels that prevent waveform ringing, thereby maintaining signal waveform stability even with longer branched wiring required for high-density pad arrangements.
Solution Approach 2:
The patent addresses the signal degradation issue by rushing through the problem with a direct impedance matching solution. By setting the characteristic impedance to a specific value, the patent quickly compensates for the negative effects of long wiring, allowing high-density configurations to proceed without extensive signal conditioning measures.
Data Source
AI summary
A first reception circuit and a second reception circuit are mounted on a printed circuit board, and receive signals via wiring thereof from a transmission circuit. The printed wiring board includes a trunk wiring, a first branched line branching from a first branch connection point, and a second branched line branching from a second branch connection point in order. A wiring area between the start end and the first branch connection point is divided into a first wiring portion and a second wiring portion, in order from the start end, and a wiring area between the first branch connection point and the second branch connection point is a third wiring portion. The characteristic impedance of the first wiring portion is set to equal or lower than the characteristic impedance of the third wiring portion, and the characteristic impedance of the second wiring portion is set higher than the characteristic impedance of the first wiring portion.