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Voltage stabilizer - RF Cafe Forums

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Below are all of the forum threads, including all the responses to the original posts.


darcyrandall2004
Post subject: Voltage stabilizer Posted: Sun May 18, 2008 8:48 am

Colonel


Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
Hello,

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.

Thankyou

_________________
Regards, Darcy Randall, Perth, Western Australia


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yendori
Post subject: Posted: Sun May 18, 2008 4:52 pm

General


Joined: Thu Sep 25, 2003 1:19 am
Posts: 50
Location: texarcana
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.

Rod


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IR
Post subject: Posted: Thu May 22, 2008 1:04 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
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.


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darcyrandall2004
Post subject: Posted: Fri May 23, 2008 1:27 am

Colonel


Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
Thanks,

Ill investigate it.

_________________
Regards, Darcy Randall, Perth, Western Australia





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