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The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl Simulators >> RF Simulators >> simulation of switched capacitor filters https://designers-guide.org/forum/YaBB.pl?num=1210932698 Message started by manodipan on May 16th, 2008, 3:11am |
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Title: simulation of switched capacitor filters Post by manodipan on May 16th, 2008, 3:11am Hi Guys, I am facing some problem in getting the ac behavior(gain and phase) for a simple switched capacitor integrator.The continuous time version of the circuit with resistors is working perfectly,but resistors replaced by switched capacitors is giving me proper transient response but not ac response.can u guys suggest some solution?pls reply asap. |
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Title: Re: simulation of switched capacitor filters Post by pancho_hideboo on May 16th, 2008, 5:04am I can't find any design issue in your post. Your question is not design issue but simple usage of EDA tool. Please post to "The Designer's Guide Community Forum ≫ Simulators ≫ RF or Circuit Simulators". manodipan wrote on May 16th, 2008, 3:11am:
Use a pulse wave having narrow width as input, then do FFT(DFT) of output transient waveform. You can use this method by any Spice type transient simulator. If you have SpectreRF of Cadence, use Shooting-PSS/PAC. See http://www.designers-guide.org/Analysis/sc-filters.pdf You can also do same tasks using HSPICE-RF of Synopsys, SmartSpiceRF of Simucad, EldoRF of Mentor or NEXXIM of Ansoft, etc... Attached figure is simple example of BP-SCF and corresponding BP-CTF. |
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Title: Re: simulation of switched capacitor filters Post by loose-electron on May 16th, 2008, 8:24am The classic "AC analysis" is applicable for continuous time systems. What you are describing is a switched system and a generic AC test doesn't work here. In a similar way of thinking, you can't simulate logic circutis in an AC analysis. |
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Title: Re: simulation of switched capacitor filters Post by buddypoor on May 17th, 2008, 2:03am Hi manodipan, there are two ways to perform an ac analysis to S/C circuits with any commercial simulation program. But first, you have to convert each time-discrete S/C unit to a time continuous replacement. This can be done with delay units which are to be designed either with transmission lines or with artificial units like controlled sources. The method is described by M.S. Ghausi and K.R. Laker in "Modern Filter Design" (Prentice Hall, 1981) and by B.D. Nelin in "analysis of switched capacitor networks using general-purpose circuit simulation programs", IEEE Trans circuits and systems, CAS-30, pp 43-48. Nelin makes use of transmission lines. Another method to realize the delay function is proposed by a tschech author, however, I have not available the reference at the moment. I will give notice later. The methods work very well and shows clearly the periodic behaviour of the transfer function. I have used it very often to demonstrate the specific characteristics of S/C to the students. It can be applied to all S/C approximations (EULER forward, backward and bilinear). Regards |
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Title: Re: simulation of switched capacitor filters Post by buddypoor on May 17th, 2008, 2:41am Hi manodipan, as an attachement I send you the mentioned document from Biolek. He proposes to model both switch phases by two parallel circuits. However, I found some mistakes in his article. If you are interested I can give you some more information - either per e-mail or within this forum. Regards buddypoor |
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Title: Re: simulation of switched capacitor filters Post by manodipan on May 17th, 2008, 4:01am Hi all, Thanx a lot for your suggestions,i hope i will be able to fix it.The pdfs are really helpful...thanx buddypoor.. |
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