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 | |  |  | | | | Resolving EMI Problems with Good Power Delivery Strategy
An interview with Kun Zhang
Huawei Technologies Co. | |
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Kun Zhang, can you first give a brief introduction on Huawei and the development in solving signal integrity and EMI problems?
Incorporated in 1988 and headquartered in Shenzhen, China, Huawei Technologies specializes in the R&D, production and marketing of telecoms equipment, providing customized network solutions in different telecom fields. Huawei is now the largest telecom vendor in China's telecom market and is quickly becoming a leading player in the global telecom market. Currently Huawei provides telecom products and solutions for over 300 operators worldwide and 22 of the world's top 50 operators are using Huawei's products and solutions. Huawei focuses on such areas as WCDMA, CDMA2000, NGN, xDSL and data communications. Huawei has 24,000 employees and sales in 2004 reached 5.58 billion USD.
SI team in Huawei was founded in 1997, which is the first SI team in China. From then on, the team has extended from several people to about one hundred engineers, who provide SI analysis for all the Huawei products. A SI lab has been founded for experiment in high speed domain. In 2004, the analysis topics have extended to signal integrity, power integrity, EMI, RF.
As one of the key Signal Integrity and EMI Engineer at Huawei, what has been the work and projects you focus on?
After joining Huawei in 2001, I have worked on several projects in SI and PI area. The first one was power integrity analysis at PCB level. Most of my projects include tool selection, device model library creation, simulation flow build up, and measurement technique research and implementation. EMI analysis is an ongoing project. The target is to provide EMI analysis for end products which have no shielding structure.
What are the challenges you and your colleagues face today in providing good solutions to Signal Integrity, Power integrity, and EMI?
There has been no critical problem in Huawei if SI and PI problems on high-speed PCBs were treated separately. For example, SI provides solutions to impedance matching, signal topology; while PI study guides stabilize power supplies. Our current focus is on solving problems caused by the combination of SI and PI issues, such as SSN and jitter. By providing good SI and PI strategies, we are aiming to solve EMI problems for end products. One of the challenges is that there is no good simulation tool available to analyze SI with PI effects.
You recently co-authored with Zhen Mu, Cadence, a DesignCon 2005 paper about Solving EMI problems through good implementation of Power Integrity scheme . What's new and interesting in this paper?
In 1989, C. R. Clayton pointed out that most EMI problems are caused by common mode noise, which is difficult to simulate and measure. Common mode noise is in fact the result of signal and power noise which could be simulated and measured. The relationship here can be described as “SI & PI => Common mode noise => EMI”.
Therefore, if signal and power noises are effectively controlled, EM radiation can be minimized. In the paper presented at DesignCon 2005, we proposed a new method to reduce power ground noise using high frequency decoupling capacitors with higher ESR. We simulated the impedance and noise of the power delivery network, measured the EMI level of evaluation board, and confirmed the close relation between PI and EMI.
Another interesting point of this paper is the cable study. Since later 80's in the last century, cable has been a critical element for EMC engineer. However, we verified that cable is only efficient from 150MHz to 300MHz. In the frequency range higher than300MHz, smaller objects in geometry become efficient, such as traces, plane pairs, and other passive components on PCB. Considering this, PI analysis is very important to resolve EMI problems.
Note: Read the paper, “Resolving EMI Problems with Good Power Delivery Strategy.”
You are also involved in providing design rules to prevent PI and EMI problems. What is your view on such an approach?
Here is what I believe. Analyses on SI, PI, or EMI, are conducted by SI/PI/EMI engineers. The simulation and measurement results help them understand problems and provide solutions. When the solutions are determined, SI/PI/EMI engineers translate the solution in the format of design rules to layout and routing engineers for final implementation. Therefore, design rules represent engineering solutions. As high speed PCB designs become more and more complicated, preventing problems according to proven solutions are much more important than correcting problems when they are detected in the end products.
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