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Simulators >> RF Simulators >> Can Spectre Solve the single-end output SC-integrator in PSS ?
https://designers-guide.org/forum/YaBB.pl?num=1248873786

Message started by larry_suyung on Jul 29^th, 2009, 6:22am

Title: Can Spectre Solve the single-end output SC-integrator in PSS ?
Post by larry_suyung on Jul 29^th, 2009, 6:22am

Hello, friends
I am trying to use Spectre to get the variance of the output noise of SC-integrator. The circuit is the same as Fig. 4, in Dr.Schreier's 2005 TCAS1 paper as attached.

The first confusing problem is that is if this is an ideal OTA, then even no input, the noise is summed in every cycle. Finally the integrated noise saturates the OTA. This can be seen in Eq(39) of attached paper.

The sesond question is that even no input, the offset and switch injection keeps the output continually ramping out at every cycle by its integration property. Therefore there is no periodic solution. So How can Spectre get the PSS and PNOISE ? But the manual said Spectre can solve SC-circuits?

Thanks so much...Larry (SuYung)

Title: Re: Can Spectre Solve the single-end output SC-integrator in PSS ?
Post by larry_suyung on Aug 2^nd, 2009, 3:07am

Dear Friends,
I derived the accumation effect of SC integrator, as attached.
The formula is confirmed with the results of W. Ki and G. C. Temes, “Offset-compensated switched-capacitor integrators,”
in Proc. IEEE Int. Symp. Circuits and Systems, May 1990, pp.
2829–2832.

My derived reults consider the offset and finite gain. This derivation is also done in Dr. Murmann's (Stanford) lecture note. But he did not include the finite gain of the OTA.

From this attached reults, it verified my last post that even no input, the single ended SC-integrator has no "periodic solution". The output goes up at every cycle. This case is different than Dr. Kendurt's paper of Simulating switched-capacitor filters with Spectre RF.

So I wonder how Spectre can handle this single-ended SC-integrator ?

Thanks so much to friends. Larry-SuYung

Title: Re: Can Spectre Solve the single-end output SC-integrator in PSS ?
Post by larry_suyung on Aug 13^th, 2009, 4:31am

Dear Friends,
I have to tune the input down to several digits to have PSS of a open loop SC integrator worked.

Maybe we should use close loop for SC integrator not open loop . Thanks