Why low Q of the resonator is good ?

[yummy]

Q of the resonator

Hi, we are designing reference oscillator IC using high Q resonator. Our senior
guy said that the Q of the resonator is not necessarily the higher the better. He
actually prefers a lower Q (range 2K~3K) instead of high Q (over 10K). Sounds
counter-intuitive to me. Anybody can help me figure out why?

Thanks.

 

[Robert A. Patterson]

Q of the resonator

It is possible that he is attempting to avoid over-voltage which could cause arcing to occur within the waveguide and damage it and other expensive components

Robert A. Patterson
https://quantumgravitics.tripod.com

 

[vfone]

Re: Q of the resonator

Lower Q of the tank needs if the design is a VCO with wide frequency range.
The result of lower Q is:
-greater phase noise (reduced tank amplitude vs. transistor noise).
-greater sensitivity to tuning-line noise (which translates directly into frequency modulation).
-potential startup problems (especially at extreme temperatures).
-greater challenge in designing the loop filter.

 

[biff44]

Re: Q of the resonator

Why don't you ask him? There could be a couple of reasons, or he could just be a crackpot.

 

[rockycheng]

Q of the resonator

A low Q will cause increasing phase noise and tank loss. So theoretically it should as large as possible.

 

[elkimhoc]

Re: Q of the resonator

if you don't care about phase noise oscillator and an exactly resonance frequency so you can use a low Q resonator

 

[qiuyangdvb]

Q of the resonator

the q is higher
the s11 of the amp is need to be higher

 

[saidtaraf]

Q of the resonator

the Q AUGMENT for lesslos

 

[jecyhale]

Re: Q of the resonator

Lower Q of the tank needs if the design is a VCO with wide frequency range.
The result of lower Q is:
-greater phase noise (reduced tank amplitude vs. transistor noise).
-greater sensitivity to tuning-line noise (which translates directly into frequency modulation).
-potential startup problems (especially at extreme temperatures).
-greater challenge in designing the loop filter.

I agree with expect the phase noise.
Amplitude will be reduced with lower Q, but usually the phase noise will increase. and with lower amplitude, the S/N will be reduced.
So far, I try to select high Q resonator especially high Q inductor for greater phase noise.
Besides, lower Q means high current.
So if you don't care the current consummation, lower Q can be employed for wide frequency range design.

 

[designtech]

Re: Q of the resonator

Its very simple..higher the Q, lower the phase noise. But sometimes bandwidth considerations limit the Q you want!