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Spectre RF By Any Other Name ...

Comments(6)Filed under: RF design, Spectre RF, DAC, ADC

It has been a while since I last appended, hope you are well!

It was a little bit difficult to come up with a subject to write about and then recently I was in a meeting where we were talking about transient noise analysis. A designer was discussing the issue of analyzing the noise of a Pipeline ADC as an example of how they use the transient noise. The conversation started me to wondering whether or not this might be a good application for Spectre RF. After all, Spectre RF PNOISE analysis can be used to analyze the noise of Sample and Hold in the Pipeline ADC. Since then I have been spent some time exploring how to use Spectre RF to analyze data conversion circuits. The experience has reminded me of the the versatility of Spectre RF's periodic steady-state and noise analysis in analyzing complex problems. Shown in Figure 1 is an example of the periodic steady-state results for an 8bit current output Digital-to-Analog Converter, DAC. The periodic steady-state analysis results can be used to measure the SFDR and THD for the DAC.



                  Figure 1: PSS Results for an 8-Bit Switched Current DAC


So back to the title, what is in a name? I have been using Spectre RF for more than 10 years and have often used Spectre "RF" for unusual applications, for example, analyzing switched-mode power supply designs. Yet this was first time I have seriously looked at Spectre RF for data converters. I too had fallen into the trap of thinking that Spectre "RF" is for "RF" circuits. In the next append, we will look further into simulating data converters with Spectre RF. In the meantime, it would be good to hear from you, have you ever used Spectre RF for non-RF applications?


Art Shaldenbrand


By Frank Wiedmann on May 4, 2009
I probably have used SpectreRF more for non-RF applications than for real RF applications like mixers etc. One application where SpectreRF has pretty unique capabilities is the simulation of jitter in data transmission circuits, both due to device noise (pnoise jitter analysis) and due to power supply disturbances (sampled pxf analysis). See www.designers-guide.org/.../YaBB.pl for some details on these capabilities.
Another application where the capabilities of SpectreRF are pretty unique is noise analysis of switched-capacitor circuits, including autozero and chopper amplifiers. These capabilities are described in detail in www.designers-guide.org/.../sc-filters.pdf . The OPA333 from Texas Instruments has been designed in this way, see the article available from ieeexplore.ieee.org/.../freeabs_all.jsp , especially section II.B.
My feeling is that Cadence is not doing a very good job of advertising these pretty unique capabilities of SpectreRF as rather few people seem to know about them and the documentation is not always very helpful. Another example for this is the pstb analysis. The corresponding application note uses an oscillator as the example although this analysis is ideally suited for stability analysis of DC/DC converters, which is also the context in which the idea for pstb analysis was born (see www.designers-guide.org/.../YaBB.pl ).

By Art3 on May 4, 2009

  Thank you for the comment. I agree that we could do more to advertise the capabilities

of Spectre RF. I had not thought about data transmission example, but you are correct

Spectre RF is also well suited for that application. BTW, we, the AE team, does have

simple workshop discussing DC-to-DC Converter simulation with Spectre RF that

includes a periodic stability analysis example. Guess we need to publish it!

By Frank Wiedmann on May 6, 2009
There is even a university course that teaches how to use pac and pnoise to simulate switched-capacitor circuits. Please take a look at the three lectures on switched-capacitor filters at ccnet.stanford.edu/.../course.cgi . I am not aware of any similar documents from Cadence.

By Frank Wiedmann on October 8, 2009
A very good example that shows how useful pstb analysis is for simulating the stability of DC/DC converters can be found at www.cadence.com/.../CD12_WerthT_iasrwth.pdf .

By Frank Wiedmann on December 8, 2010
Another good example for simulation of switching regulators with pss/pac analysis can be found at www.edn.com/.../472586-Periodic_steady_state_and_small_signal_analyses_of_switching_regulators.php .

By Frank Wiedmann on August 20, 2014
The address of this article is now edn.com/.../Periodic-steady-state-and-small-signal-analyses-of-switching-regulators .

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