Voltage stabilizer - RF Cafe Forums
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Post subject: Voltage stabilizer Posted: Sun May 18, 2008 8:48 am
Joined: Tue Feb 27, 2007 6:16 am
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 the VCO.
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.
Darcy Randall, Perth, Western Australia
Post subject: Posted: Sun May 18, 2008
Joined: Thu Sep 25, 2003 1:19 am
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
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 traces.
In addition, for VCO
supply there is a specific circuit known as:
''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.
There 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.
Post subject: Posted: Fri May 23, 2008 1:27 am
Joined: Tue Feb 27, 2007 6:16 am
Ill investigate it.
Regards, Darcy Randall, Perth, Western Australia