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 16^th, 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.

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

Hi all,
Thanx a lot for your suggestions,i hope i will be able to fix it.The pdfs are really helpful...thanx buddypoor..