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: Voltage stabilizer Posted: Sun May
18, 2008 8:48 am
Joined: Tue Feb 27, 2007
I was reading the text, "Phase
noise in Signal Sources". The text illustrated an example, 10^-6 noise
voltage, a VCO with a Kvco of 15MHz/Volt, at 150Hz this produces a single
sideband phase noise density of -23dBc/Hz.
To avoid this problem,
the text recommended the uses of voltage stabilizers placed close to
Aside from the obvious use of plenty of noise decoupling
capacitors, what devices do you believe the text is referring to?
Ive been searching for voltage stabilizers but all I come across
are voltage regulators.
Obviously a voltage regulators role
is to provide a somewhat stable voltage. Nevertheless are there voltage
regulators available designed specifically to be placed close to the
supply of the VCO, offering extremely low noise ripple and can you refer
me to any?
Typically in designs, I have always just used one
regulator to supply a number of components and the regulator is often
placed miles away from the devices it supplies.
Regards, Darcy Randall, Perth, Western Australia
Post subject: Posted: Sun May 18, 2008
Joined: Thu Sep 25, 2003 1:19 am
I have always used a Low noise
regulators to supply only the VCO.
And a dedicated regular for
the op amp (loop filter) as well.
It's the ideal approach for
obvious reasons. Of course, there are size and cost considerations.
Post subject: Posted: Thu
May 22, 2008 1:04 pm
Joined: Mon Jun 27,
2005 2:02 pm
A voltage regulator
(Or more commoonly known nowadays as LDO Regulator - Low Dropout Regulator)
is an important measure the reduce the phase noise in VCO and PLL circuits.
The LDO should be placed as close as possible to the VCO supply
rails, by this the supply voltage will not pick up noise along the long
In addition, for VCO supply there is a specific circuit
''Super Filter'', which consists of a NPN transistor with
voltage divider at the base. The base is decoupled to GND with several
capacitors (uF to nF range) in paralles to the base-GND resistor. The
emitter is connected directly to the VCO supply while the collector
is connected to the Vcc. This circuit drops the supply voltage to the
required VCO supply level while providing filtering to the supply voltage.
The Vcc has of course to be higher than the VCO voltage.
are several companies which manufacture LDO's. I can recommend on Maxim
(www.maxim-ic.com) and Micrel (www.micrel.com) which have LDO's product
lines of LDO's.
Posted: Fri May 23, 2008 1:27 am
Tue Feb 27, 2007 6:16 am
Regards, Darcy Randall, Perth, Western