High-speed passive link impedance matching routine

optimization in simulationHFSScomplex models,经常会发现,If the optimization adjusts a certain structure size,高频VSWRIndicators and low frequenciesVSWRThere is a seesaw phenomenon in the indicator,按下葫芦起了瓢！

The owner of the island has seen someone optimize a large scale with a high-performance serverHFSS模型,More than ten structural dimensions are all parameterized,Set the full frequency rangeVSWR指标,然后启动HFSS优化,7X24Hours of non-stop blind running.

This blind optimization,I am afraid that even if the universe is destroyed, the optimal solution will not be obtained,I'm dying！

何以解忧？Only tricks.

套路一：Where to segment？

The picture below is from Baidu：

 

芯片~封装~子板PCB~连接器~High-speed backplane~连接器~子板PCB~封装~A high-speed passive link composed of chips,在设计阶段,Follow this link hereA、B、CThe position is broken into four pieces：

• Chip package carrier board~子板PCB
• 子板PCB~高速连接器~背板
• 背板~高速连接器~子板PCB
• 子板PCB~Chip package carrier board

If the link is symmetrical,Then only half of the link needs to be considered,That is two pieces.

当然,Passive links can still be subdivided.Typical chip package carrier/SIP结构如下图所示：

 

A chip package carrier like the one shown above~子板PCBThis link can be further subdivided into the following two segments：

• 芯片~Bonding~封装载板
• 封装载板~BGA焊球~子板PCB

The segment location must be on a transmission line that is dimensionally stable in cross-section,That is, where the impedance is continuous,例如PCB微带线、带状线、同轴电缆.

 

The figure above is the differential via simulation model,The cross-sectional dimensions are unchanged（Impedance is continuous）的PCBBreaking the wiring is normal practice.

套路二：Low frequency first,After the high frequency.

Some high frequency passive links,Because the wavelength of the high-frequency signal is almost comparable to the cross-sectional structure size,Simulation or testingTDRIndicators don't work anymore！

optimization in simulationHFSScomplex models,经常会发现,If optimizing a certain size,高频VSWRIndicators and low frequenciesVSWRThere is a seesaw phenomenon in the indicator,按下葫芦起了瓢！

怎么办呢？

Play low frequencies first,After the high frequency.Examples illustrate specific practices：

 

 

上图VSWRThe curve is high frequency66GHz同轴连接器PCBSimulation metrics for transforming structural models

（A follow-up article will specifically explain how to position it64GHzResonant spike problem,敬请关注本公众号：See pictureRF）.

The blue line is our expected passive linkVSWR指标模板,Depending on passive link complexity（或经验）Select the template slope;

Red line on original modelVSWR曲线,red line in8~18GHzThe low frequency band exceeds the template,Adjust a structure size first,Force down8~18GHz低频段的VSWR指标;

Then keep the size of this structure unchanged,Another structural dimension of the passive link is adjusted,压下38~66GHz高频段VSWR指标;

The optimized model corresponds to that shown by the green lineVSWR指标.

The rationale behind this approach is：

Low frequencies are the foundation,High frequencies are buildings.

基础不牢,地动山摇.

总结

Complex passive link simulation optimization routine：

ü  Complex passive links can be broken down for simulation optimization,The breaking point must be on a transmission line with a stable cross-section,That is, where the impedance is continuous.

ü  Optimize a certain size,高频VSWRIndicators and low frequenciesVSWRThere is a seesaw phenomenon in the indicator,按下葫芦起了瓢！怎么办？Play low frequencies first,After the high frequency.

出品｜EDA365

作者｜何平华老师