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Design >> RF Design >> phase noise questions?
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Message started by liletian on May 4^th, 2009, 8:49am

Title: phase noise questions?
Post by liletian on May 4^th, 2009, 8:49am

Hi Guys
I had a measured results shows the following spectrum of ring oscillator, it seems the spectrum is dirty, any suggestions what the phase noise source might be? I do not think it is flicker noise since it is at the 10Mhz region, am I right? Also, is their paper or post about VCO layout techniques? I would like to make a PLL, but I want to isolate VCO from mixer and amplifier stage if possible.
Thanks

Title: Re: phase noise questions?
Post by pancho_hideboo on May 4^th, 2009, 8:53am

liletian wrote on May 4^th, 2009, 8:49am:

I had a measured results shows the following spectrum of ring oscillator,
it seems the spectrum is dirty, any suggestions what the phase noise source might be?

It is not suprised at all that spectrum is dirty because your ring oscillator is free running state.

But I can't figure out your situations any more with only spectrum.

How to probe signal ?

What instruments do you have and use ?

Can you measure envelope_amplitude v.s. time ?
Can you measure Frequency Deviation v.s. time ?

Title: Re: phase noise questions?
Post by liletian on May 4^th, 2009, 9:05am

pancho_hideboo wrote on May 4^th, 2009, 8:53am:

liletian wrote on May 4^th, 2009, 8:49am:

I had a measured results shows the following spectrum of ring oscillator,
it seems the spectrum is dirty, any suggestions what the phase noise source might be?

Can you explain more free running state?
In which state it will be better spectrum?
how yo measure envelope_amplitude v.s. time ?
Frequency Deviation v.s. time ?
what's the use of it?
I use agilent spectrum analysizer to measure it and GSG probe.

Title: Re: phase noise questions?
Post by pancho_hideboo on May 4^th, 2009, 9:11am

It seems you don't have much experiences of actual measurements.

liletian wrote on May 4^th, 2009, 9:05am:

Can you explain more free running state?

It is "not locked state".

liletian wrote on May 4^th, 2009, 9:05am:

In which state it will be better spectrum?

You don't seem to understand VCO, PLL, etc.

liletian wrote on May 4^th, 2009, 9:05am:

I use agilent spectrum analysizer to measure it

There are many spectrum analyzer in Agilent.
http://www.home.agilent.com/agilent/product.jspx?nid=-536902453.0.00&cc=US&lc=eng
But I think your spectrum analyzer have built-in VSA89600 Vector Signal Analysis ability. Is it right ?

liletian wrote on May 4^th, 2009, 9:05am:

how yo measure envelope_amplitude v.s. time ? Frequency Deviation v.s. time ?

Use VSA89600 Vector Signal Analysis.

liletian wrote on May 4^th, 2009, 9:05am:

what's the use of it?

You can distinguish AM-Noise and PM(FM)-Noise.

liletian wrote on May 4^th, 2009, 9:05am:

and GSG probe.

I don't mean what probe you use.

It seems 50ohm is loaded directly in your observation point of circuit.
Your observation point of circuit have enough ability to drive load of 50ohm ?
Does it require high-impedance probing, such as Giga-Pico-Probe ?

Title: Re: phase noise questions?
Post by liletian on May 5^th, 2009, 8:08pm

pancho_hideboo wrote on May 4^th, 2009, 9:11am:

It seems you don't have much experiences of actual measurements.

liletian wrote on May 4^th, 2009, 9:05am:

Can you explain more free running state?

It is "not locked state".
so for unlocked state, the spectrum is very dirty?

liletian wrote on May 4^th, 2009, 9:05am:

In which state it will be better spectrum?

You don't seem to understand VCO, PLL, etc.
I do, I read a lot books, but not as much experience yet.

liletian wrote on May 4^th, 2009, 9:05am:

I use agilent spectrum analysizer to measure it

how yo measure envelope_amplitude v.s. time ? Frequency Deviation v.s. time ?

Use VSA89600 Vector Signal Analysis.
Thanks, I will read manual and try to do it.

liletian wrote on May 4^th, 2009, 9:05am:

what's the use of it?

You can distinguish AM-Noise and PM(FM)-Noise.

liletian wrote on May 4^th, 2009, 9:05am:

and GSG probe.

I don't mean what probe you use.

It seems 50ohm is loaded directly in your observation point of circuit.
Your observation point of circuit have enough ability to drive load of 50ohm ?
yes, definitely!
Does it require high-impedance probing, such as Giga-Pico-Probe ?
no, for oscillator point, we did not need it!

Title: Re: phase noise questions?
Post by pancho_hideboo on May 6^th, 2009, 8:55am

liletian wrote on May 5^th, 2009, 8:08pm:

so for unlocked state, the spectrum is very dirty?

Not so dirty as your spectrum. Your spectrum is very dirty.
And floors of your spectrum are very high and dirty.
I suspect PSRR(POwer Supply Rejection Ratio) of your VCO.
Is PSRR of your VCO enough large ?

You should consult someone who has much experience of actual RF measurements about your measurement setups and usages of instruments.

liletian wrote on May 5^th, 2009, 8:08pm:

pancho_hideboo wrote on May 4^th, 2009, 9:11am:

yes, I did not use this feather yet.:)

??? feature ?

Title: Re: phase noise questions?
Post by liletian on May 6^th, 2009, 9:08am

pancho_hideboo wrote on May 6^th, 2009, 8:55am:

liletian wrote on May 5^th, 2009, 8:08pm:

so for unlocked state, the spectrum is very dirty?

Not so dirty as your spectrum.
Anyway floors of your spectrum are very high and dirty.
I suspect PSRR(POwer Supply Rejection Ratio) of your VCO.
Is PSRR of your VCO enough large ?

You should consult someone who has much experience of actual RF measurements about your measurement setups and usages of instruments.

liletian wrote on May 5^th, 2009, 8:08pm:

pancho_hideboo wrote on May 4^th, 2009, 9:11am:

yes, I did not use this feather yet.:)

??? feature ?

function :(

Title: Re: phase noise questions?
Post by pancho_hideboo on May 6^th, 2009, 11:04am

liletian wrote on May 6^th, 2009, 9:08am:

pancho_hideboo wrote on May 6^th, 2009, 8:55am:

liletian wrote on May 5^th, 2009, 8:08pm:

pancho_hideboo wrote on May 4^th, 2009, 9:11am:

yes, I did not use this feather yet.:)

??? feature ?

function :(

Unbelievable typo !!