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https://designers-guide.org/forum/YaBB.pl Design >> Mixed-Signal Design >> DAC clock jitter https://designers-guide.org/forum/YaBB.pl?num=1117897806 Message started by Visjnoe on Jun 4th, 2005, 8:09am |
Title: DAC clock jitter Post by Visjnoe on Jun 4th, 2005, 8:09am Hi, I'm currently investigating (@ the architectural level) a 12b delta-sigma (oversampling) CMOS DAC. One of the main non-idealities associated with CMOS ADCs/ DACs is the clock jitter. Modeling of clock jitter for ADCs is fairly straightforward: one just assumes 'ideal clock instants' but adds a certain deviation dv to the 'ideal sampled values'. Afterwards, FFT processing of the data shows the effect of the clock jitter. However, for a DAC, i can't come up with a way to model the clock jitter...of course, generating a clock with jitter is not the problem, but data that is generated in such a way can not be used for FFT processing (requires equidistant points). Does anyone have an idea and/or experience with modeling of clock jitter effects on DAC performance? Thanks a lot! Peter |
Title: Re: DAC clock jitter Post by Ken Kundert on Jun 4th, 2005, 8:46am If you have access to Spectre you can use it. It provides two ways of performing a Fourier analysis. The FFT, built into Artist, is a discrete-time Fourier transform. The Fourier component, built into Spectre itself, computes the true Fourier integral, and so is a continuous-time Fourier transform. It will accurately catch the jitter. -Ken |
Title: Re: DAC clock jitter Post by Visjnoe on Jun 6th, 2005, 5:11am Hi, Does anyone know an alternative to using the continous FFT (requiring SpectreRF)? Greetings Peter |
Title: Re: DAC clock jitter Post by sheldon on Jun 6th, 2005, 8:07am Visjnoe, Ken described Spectre's Fourier Analysis. This analysis is a basic capability of Spectre and does not require a SpectreRF license. However, the fourier element implemented in analogLib is only a subset of the full functionality and you should probably run Spectre from the command line(unless you want to modify the CDF yourself). BTW, Spectre's Fourier analysis is described in chapter 5 of Ken's book. Also had a question for Ken :-) , when using the fourier integral for analyzing oversampling ADC/DAC is there any method to window the data? Since for oversampling ADC/DAC the data is not periodic outside the time selected for the Fourier analysis, it seems like the data needs to be windowed to prevent spectral leakage. Best Regards, Sheldon |
Title: Re: DAC clock jitter Post by Ken Kundert on Jun 6th, 2005, 9:30am Sheldon, The only way I know to apply a window to the Fourier Integral components in Spectre is to add Verilog-A code between the Fourier component and the rest of the circuit that implements the window. Peter, The only alternative to Spectre's Fourier Integral that I know of is to build a Fourier analyzer directly into your circuit using multipliers, integrators, etc. Each harmonic requires a sine and cosine source, two multipliers, and two gated integrators. Such an analyzer can be implemented using Verilog-A. You would only want to do this if you were interested in very few harmonics (say no more than 3). -Ken |
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