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Looking for another article on Crystal oscillator by Authors !!!

After reading this article, I consoled myself in way that mystery behind ultra low phase noise performance of Crystal oscillator is resolved and no longer exist in the form of cut and try method till we get frustrated and ended with prototype lab model without repeatability. Indeed, Leeson formula gave good direction to begin with but new formula described in this article can be used optimization of the performances for high end signal sources. Author's other book "Design of Modern Microwave Oscillators for Wireless Applications" explains most of the oscillator design methodology and worth reading for understanding this article in depth. Prof Rohde should write another book on oscillator for removing the shadow of mystery behind oscillator design otherwise we are going to make same mistake while designing integrated oscillator in Si/GaAs/CMOS foundry.

According to the book “RF/Microwave Circuit Design for Wireless Applications” by U. Rohde and D. Newkirk (ch 5, pg 736), the Flicker Noise corner was introduced for the first time into Leeson formula by Dieter Scherer from HP in 1978.

I am asking myself why when introducing this new parameter which makes a big impact on the final phase noise prediction, there are so many RF engineers that still use in their modeling the basic Leeson formula.

Lot of info. but too complex to understand the circuit as shown in Figure 7.

Your online article is unprintable. Attempting to print directly from the webpage or from the "Printer-friendly" view results in the page extending beyond the margins of the paper, even when print margins are set to zero.

RF MEMS based low cost oscillator may replace expensive crystal oscillator for the applications where high performance ref. source is very critical. This paper describes techniques to lower the phase noise but author did not elaborate in details about the degree of freedom for selecting lower Q resonator. Readers like us may not figure out the ratio of the Q factor and impact on performances.

What compromise we have to make for low Q crystal oscillator versus high Q crystal oscillator? In general, phase noise performance will be influenced with greater degree but this paper describes the way to overcome this problems but at what price? Whether price is to compensate by circuit complexities or other performance such as tuning range, puliiling/pushing, output power, power consumption, size, and thermal drift. I like this paper because of clear mathematical derivation that allows reserach scholar to test and verify the experimental results. Regards, Tiazurelio, PhD. Student (UK)

Can we extend the operating frequency of the VCXO based on discussed techniques in the paper ? Author may like to address this issue and comments about the higher order overtone mode for the realization of oscillation in 1.2/2.4 GHz range.

Crystal resonator vibrates due to the piezoelectric effect,and by default we get overtone frequency modes in addition to the fundamental. The mystery of undesired mode jumping is a major drawback in overtone mode VCXO circuit. Not much detailed explanation is given about how to suppress the undesired jumping modes, authors perhaps would like to address this problems/solutions in next issue of journal based on referred patented approach in the cover page of the journals (August Issue).

Yes, there is too much math but the article seems to address in the good way the solution versu phase noise. Congratulations

Gian

To all:

While this paper does not give all the details of the patented approach, i would like to add that here we really addressing a VCXO, a voltage controlled VHF crystal oscillator. Certainly we ha in realty a isolating buffer amplifier and the control voltage corrects aging and thermal drifting.

However the same principle applies to a frequency standard like a 10 MHZ oscillator.

If you send me an e-email at ulr@synergymwave.com I can supply you with information on the VHF/UHF VCO technique.

Can't think of better article than this about Crystal oscillators.I'm concern about the pulling/pushing and thermal drift but it seems that patented techniques explained in the Figure 7 will minimize the drift. We will be ordering few crystal oscillators for our reference signal source in space applications.

Good paper. We always find articles on oscillators based on cut & try approach or experimental results without proper explanations that leaves behind mystrey about autonomous systems. I'm amazed by reading this article and convey my regards to authors for giving good insights about crystal oscillators. I will be teachning crystal oscillator based on this paper to graduate students and will add some of the examples as a minor projects.

We seldom find paper on oscillator like this. After reading this article, I am developing keen interest in designing low noise crystal oscillator by using higher order overtone modes as a cost-effective alternative.

To: Dr. Hoogle V.

We have submitted a paper to IEEE Transactions on Circuits and Systems, titled : " A Novel Grounded Base Oscillator Design for VHF/UHF Frequencies"

which gives a long derivation as well as a "magical" scalable very simple solution suited for 2 min calculation. It covers the general Oscillator optimization problem.

Let us hope is has the right mix of math, practical details and measurements for the IEEE standard. These things are so specialized that finding a good place for a presentation is difficult. Conference proceedings are not readily available and the IEEE papers can have a turnaround time of up to 2 years !!!

Ulrich L. Rohde, PhD, ScD, August 21 , 2007

Excellent article by a pair of the leading engineers in this area. The mathematical treatment is excellent.

I am a PhD student, found this article good for my reference.

Linear approach for oscillator's performance analysis is just a starting condition and does not lead to any specific design goal due to many unknown time varying parameters. Among the more difficult oscillator performance parameters to predict are output power, noise figure, operating Q, and flicker corner frequency. Authors did show the way to overcome the above problems but do require complex large-signal time dependent noise dynamics. It would be appreciated if there is quick and short-cut formulation of the phase noise model based on predominant noise generating sources such as base current, collector current, base spreading resistance, tank loss resistance, flicker noise etc. Authors describe individual contribution of noise sources and finally total phase noise at different offset frequency, however, this exercise is rigorous and practically not feasible for design engineers. The better approach would be if individual noise sources automatically set for optimization and minimization depending upon their magnitudes for a given operating frequency and ratio for a given noise sources in the oscillators and perhaps connected with the linear phase noise model.

Article is too mathematical but gives state-of-the art design techniques to achieve low phase noise without using expensive very high Q crystal resonator.