选择SMT电容时，SRF和ESR的意义何在？

http://tiny.cc/rdtb2w http://tiny.cc/oftb2w



     以下为原文

  http://tiny.cc/rdtb2w
http://tiny.cc/oftb2w

Volker Sir，非常感谢你的帮助。



     以下为原文

  Volker Sir,
               Thank you very much for  your help.

亲爱的先生，感谢您的帮助，以显示有用的链接。
我已经浏览了这两个文件，这些文件没什么用处。
我需要具体说明，我们如何找到特定电容值的SRF（串联谐振频率），以及如何使用公司数据表图表以及我们从ESR中学到的东西来读取特定电容值的SRF值。
我没有发现SRF＆amp; amp;
ESR很多信息。很抱歉。



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  Dear Sir,
               Thank you for your help to show the usefull link. I have gone through those two documents, those are not much useful. I need specifically, how we have to find the SRF( Series Resonant Frequency) for the particular capacitor value and how we have to read the SRF value for particular   capacitor value using company datasheet graph and what we can learn from the ESR. I didn't find the  significance of SRF &  ESR much information.I am sorry.

但是这些文件对您关于SRF和ESR的问题有非常明确，详尽的答案。
尝试再次阅读。
对于SRF图的解释，要找到给定值和包大小的SRF值，可能图片有助于我添加一些注释。
关于选择电容器封装尺寸的一般性评论： - 所有电容器都具有寄生效应，如等效电路型号所示。
其中两种寄生效应是有效串联电阻（ESR）和串联电感。
- 如果您将电路模型或S参数用于电容器，并且具有适合您的电容器类型的模型，则包括所有这些寄生效应。
- 串联电感导致频率相关的有效电容。
在自谐振频率（SRF）下，寄生电感抵消了电容。
在上面，电容表现为电感性的。
- 如果您需要使用capactor来阻止DC，并且不关心确切的值，则可以在宽频率范围内使用它。
- 如果需要精确的电容值，寄生电感和产生的SRF很重要，因为它们会改变有效电容。
- 对于不同的封装尺寸，AVX电容器的串联电阻大致相同。
哪个最适合你？
- 包裹代码表示尺寸。
较小的数字=较小的包裹。
图片：http：//tiny.cc/bnnd2w - 某些值可能仅适用于小/大包装尺寸。
- 较小的封装具有较小的寄生电感和较高的SRF，因此它们的行为更像理想电容。
- 更大的封装具有更高的寄生电感，但通常可以处理更高的电压（不是LNA的问题）。
- 更大的封装可能更容易处理/焊接。



     以下为原文

  But these documents have very clear, detailed answers to your question on SRF and ESR. Try to read it again.

For interpretation of the SRF graph, to find your SRF value for given value and package size, maybe the picture helps where I have added some notes. 

General comments on choosing the capacitor package size: 

- All capacitors have parasitics, as seen in their equivalent circuit models. Two of these parasitics are effective series resistance (ESR) and series inductance. 
- If you use circuit models or S-parameters for the capacitor, and have the exact model for your capacitor type, all these parasitics are included.
- Series inductance leads to a frequency dependent effective capacitance. At the self resonance frequency (SRF), the parasitic inductance cancels the capacitance. Above, the capacitor behave inductive.
- If you need the capactor to block DC, and don't care much about the exact value, you can use it in wide frequency range.
- If you need an exact capacitance value, the parasitic inductance and resulting SRF is important, because they change the effective capacitance. 
- Series resistance for your AVX capactors is about the same for different package sizes.

So which is best for you? 
- The package code indicates size. Smaller number = smaller package. Picture: http://tiny.cc/bnnd2w
- Some values might be available only in small/large package dimension.
- Smaller packages have smaller parasitic inductance, and higher SRF, so that they behave more like ideal capacitors. 
- Bigger packages have higher parasitic inductance, but can usually handle higher voltages (not a problem with your LNA).
- Bigger packages might be easier to handle/solder.

附件

• readSRF.PNG193.5 KB