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Posted by Heider Marconi on March 21, 2009, 11:29 pm
Hey there. I've been working with oscillator design for some time now but I had never characterized one before now. The measured phase noise is 20db above what it should be in simulation, design and specification. I tend to think it is a problem in test procedure. My oscillator was designed in 0.35um AMS tech and is running at 1GHz. I'm using an RF CASCADE probe station, AGILENT DC power source, KEITHLEY source meter as a current souce and a ROHDE&SCHWARZ spectrum analyzer and no passive components so far.
Any help, from books, articles or former experienced engineers' tips are very welcome.
Thank you all.
Heider Marconi

Replies to This Discussion

Reply by Jesal Mehta on March 22, 2009, 1:13 pm
20-dB seems high. What level are you trying to measure in dBc/Hz? How do you measure it. Do you subtract resolution BW of the spectrum analyzer from the spectrum. Can you tell me your setup and measurement procedure.
Reply by Heider Marconi on March 24, 2009, 11:14 pm
Ok then...I will describe the procedure with more details.I am trying to measure something around -107dBc/Hz. The oscillator is a differential complementary cross-coupled LC VCO.I reduced the analyzer bandwidth to it's minimum during measurement.I actually have serious trouble with the polarization, Vdd, control voltage and a bias current. As I am using a Cascade probe station and the lab does not have the DC probes I am using the RF ones to do the job. I have checked the power levels and the probes can easily take the current needed.Beside that, the cables I am using are optimized for RF too with SMA connectors and we do not have the adapters from the DC bournes to SMA. So I am using single wires to get the bias voltage and current from the sources to the circuit counting on that the DC voltages will not couple a lot. That is the greatest problem in the procedure but by now I do not see other solution.And as a result of the measurement the noise floor rises from -100dBm to something around -40dBm. This is obvious a noise up-conversion but I cannot find the problem.I think you can get an idea of the whole thing now.Thankyou for the help!
Reply by Jesal Mehta on March 27, 2009, 3:48 pm
Looks like bias noise is getting upconverted. A figure describing the measurement topology will be good to in investigate the actual problem
Reply by Heider Marconi on April 2, 2009, 11:35 pm
how can I upload a picture here?sorry to take so long...Things have been tough at work...
Reply by Heider Marconi on April 5, 2009, 7:37 pm
despite all the difficulties I faced in characterizating the oscillator I submited a paper to a conference in Brazil. if you want to read it please leave your e-mail so I can send you. I don't have the answer if it was accepted yet.but the work on it is not finished.
Reply by Heider Marconi on April 13, 2009, 9:58 pm
ok... my email is hmalkav@yahoo.comI have some unusual results I cannot explain...for some reason the function between control voltage and output frequency has discontinuities... If you are interested write me and I'll send you the paper...thankyou
Reply by Heider Marconi on April 16, 2009, 2:51 pm
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