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https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> Re: about sc filter simulation https://designers-guide.org/forum/YaBB.pl?num=1079855301 Message started by Ken Kundert on Mar 21st, 2004, 11:54pm |
Title: Re: about sc filter simulation Post by Ken Kundert on Mar 21st, 2004, 11:54pm Alice, What type of circuit follows your switched-capacitor filter? Is it a sampled-data circuit, such as a sample and hold or ADC, or is it a continuous-time circuit, such as a continuous-time anti-alias filter? A sampled-data circuit is only sensitive to the noise your SC filter produces at the instant when it samples, while a continous-time circuit is sensitive to noise produced at all time during the clock cycle. If your SC filter is followed by a continuous-time circuit, then you are interested in the continuous-time behavior. SpectreRF computes this directly. If your SC filter is followed by a sampled-data circuit, then you are interested in the discrete-time behavior of your circuit. In this case, you must either use SpectreRF's strobed-noise feature or add an ideal sample-and-hold to the output of you circuit so that only the noise at the sample point is measured. -Ken |
Title: Re: about sc filter simulation Post by Ken Kundert on Mar 22nd, 2004, 10:46pm In my experience, you do not want to make things too ideal when simulating switched-capacitor circuits with circuit simulators. Particularly in regards to the switch. Infinite off resistance might be okay, but be sure the on resistance is reasonable. By reasonable, the switches on resistance should mimic the resistance produced by real CMOS switches. Using ideal capacitors and opamps should not cause difficulties. If you are using switches that exhibit a reasonable on resistance, and you are still having trouble, then I would carefully check your circuit to make sure that it is correct. -Ken |
Title: Re: about sc filter simulation Post by Ken Kundert on Mar 23rd, 2004, 7:45am You don't say how it is failing to converge. Is it failing to converge in DC, in transient or the tstab interval of PSS, or is the outer PSS iteration failing to converge. -Ken |
Title: Re: about sc filter simulation Post by Ken Kundert on Mar 24th, 2004, 7:35am I'm afraid I cannot help you with practical design questions. Sorry. -Ken |
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