Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Factor affecting the phase noise in oscillator Posted: Tue Nov 21, 2006 3:59
Joined: Tue Oct 03, 2006 3:03 am
I am interested to
know what are the factor which can effect the phase noise of the oscillator other than the Q of the Resonator.
Post subject: Posted: Wed Nov 22, 2006 7:29 am
Mon Jun 27, 2005 2:02 pm
The other factors which
affect phase noise are:
1. The NF of the active device.
2. The offset frequency from the center
frequency (At which the phase noise is being measured)
3. The average power through the resonator circuit and
4. The Flicker corner frequency of the active device.
5. Temperature of operation.
These factors are included in the Lesson's formula which defines the phase noise of an osscilator.
look at this link which gives a good overview:
http://www.zen118213.zen.co.uk/Systems_ ... eNoise.pdf
Post subject: Posted: Wed
Nov 22, 2006 8:50 am
Joined: Fri Feb 17, 2006 12:07 pm
The only thing I would add to IR's very comprehensive reply would be the presence of
any dissimilar metal contact that can give rise to intermodulation (at very low level, but significant). The
spectral noise lines resulting from all the processes mentioned by IR then mix with each other and thus spread
component sidebands even further out from the carrier. Thus the slope of dBW/Hz is therefore reduced.
Post subject: Posted: Wed Nov 22, 2006 9:27 am
Joined: Mon Jun
27, 2005 2:02 pm
Another issue which is more physical rather than
electrical is of course PCB layout. You need to follow good PCB layout practices in order to achieve good phase
In addition to that, you should apply adequate filtering to the oscillator's supply
rails. There is even a special circuit known as "Super Filter" which is made of an NPN transistor including bypass
capacitors of several values at both the NPN's base and collector. This circuit reduces the voltage from the
supply to the level required by the oscillator. The emitter of the NPN is connected to the supply rail of the
active device in the oscillator circuit. The only disadvantage is that you need to provide a higher voltage to the
NPN's collector due to the Vce voltage drop. The NPN's DC operating point is set with voltage divider in the base.
I hope that you understood from the description how the circuit looks like and operates.