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fixed capacitance and variable capacitance in cadence.

imagesensor123

 Hi,

    when i use "captab" function to print out the node capacitance, i found there are two kinds of capacitors, can anybody explain the difference between them? is there a skill function which can monitor  a node capacitance time to time? in fact, i have a column of transistor whose source was connected  together.in a simple word, is that the node capacitance (connect ten source together) equal to ten times of the capacitance of only one soure ?

regards,

zfeng

  • Hi zfeng

    1. Please search for "Printing the node capacitance table" in $MMSIMHOME/doc/spectreuser/spectreuser.pdf for an explanation of the results of captab.

    2. No, I don't think that there is a skillscript to monitor node capacitance. I think perhaps you need to explain more on your objective.

    3. I would indeed expect the capacitance to be much more that of a single device but it might not necessarily be 10x due to the layout placement. E.g. abutted devices would give less capacitance. Pehaps you can run captab to confirm this. : )

    Best regards
    Quek

  • Hi Quek,

        commonly, do people need to monitor the node capacitance? i ma trying to find the column capacitance( a number of transistors source node connect together in parallel) , and i am also agree with you about the capacitance in layout, what's your method of observing a node capacitance changes versus time during the transient simulation?

  • Hi zfeng

    I think it really depends on the design and if there is a need do so. I don't really monitor node capacitances myself. To monitor the change in node during a transient run, please use "infotimes" together with captab function. Please search for "infotimes" in $CDSHOME/doc/anasimhelp/anasimhelp.pdf.


    Best regards
    Quek

  • Hi Quek,

        thanks for your explanation, and i am trying to use the function "infotimes" combined with "captab" to achieve this, thank you again.

     

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