Signal Integrity Research of High Speed Circuit of Embedded System Kaihua Xu 1, Jun Zhou 1, Yuhua Liu 2, and Shuyun Dong 1 1 College of Physical Science and Technology, HuaZhong Normal University, Wuhan , China 2 Department of Computer Science, HuaZhong Normal University, Wuhan , China phy.ccnu.edu.cn

Overview What is Signal Integrity (SI)? What is crosstalk? What is reflection ? The mechanisms of crosstalk and Reflection Signal integrity simulation SI Roles

What is Signal Integrity (SI)? That ensures all signals transmitted are received correctly That ensures signals don ’ t interfere with one another in a way to degrade reception. That ensures signal don ’ t damage any device That ensures signal don ’ t pollute the electromagnetic spectrum

Crosstalk is the coupling of energy from one line to another via:  Mutual capacitance (electric field)  Mutual inductance (magnetic field) What is crosstalk? Mutual Inductance, L m Zs Zo CmCm LmLm Zs Zo Mutual Capacitance, C m near far near far

The near and far end victim line currents sum to produce the near and the far end crosstalk noise What is crosstalk? Zs Zo Zs Zo I Cm LmLm near far near far I Lm

What is reflection ? Transmission line impedance changes, reflection occurs

What is reflection ? Minimize reflections Use controlled impedance interconnects Provide at least one termination at the ends of a transmission line. Use a routing topology that minimizes the impact from multiple branches. Minimize any geometry discontinuities.

The circuit element that represents this transfer of energy are the following familiar equations Mechanism of Mechanism of crosstalk The mutual inductance will induce current on the victim line opposite of the driving current (Lenz ’ s Law) The mutual capacitance will pass current through the mutual capacitance that flows in both directions on the victim line

Mechanism of Mechanism of crosstalk TD 2TD ~Tr far end crosstalk Near end crosstalk Zo V Time = 2TD Zo Near end current terminated at T=2TD V Time = 0 Zo Near end crosstalk pulse at T=0 (I near ) Far end crosstalk pulse at T=0 (I far ) Zo V Time= 1/2 TD Zo V Time= TD Zo Far end of current terminated at T=TD

Mechanism of Mechanism of reflection We have a equation for the reflection equation can simplify change into a simple distribution network, such as

Mechanism of Mechanism of reflection Graphical Explanation Graphical Explanation

Signal integrity simulation Main Board Structure s3c2440,6—layer mainboard GPRS wireless communication module GPS module Simulation Tools and Environment Mentor Graphics Corporation’s Hyperlynx IBIS model

Signal integrity simulation crosstalk network

Signal integrity simulation Photo on PCB

Signal integrity simulation after then end-to-end source signal

SI Roles Convert product parts and design features into models and parameters Use models to simulate performance Perform measurements to validate product Determine how parameters limit performance Use cost and simulated or measured performance to determine rules for design Use margin budgets to manage designs

Any queation? Thank you! Decmber 15,2009