Phase noise effect in receiver performance

[abhijitrc]

HOW LOCAL OSCILLATOR PHASE NOISE EFFECT THE RECEIVER PERFORMANCE?, WE ARE PLANNING TO GENERATE A CARRIER FREQUENCY AT KU BAND( 13.9 GHz), OUR APPROACH WILL BE EITHER:

1.A SYNTHESIZER(PLL BASED) WHICH GENERATES 6.95GHz, AND LATER THE OUTPUT OF THE PLL IS MULTIPLIED(X2) BY AN ACTIVE DOUBLER CIRCUIT TO GENERATE ~13.9GHz .OR

2. DIRECT SYNTHESIS OF 13.9GHz USING PLL .?

WHICH METHOD WILL BE BETTER IN TERMS OF LOW PHASE NOISE?? AND HOW IT EFFECTS THE RECEIVER PERFORMANCE!! KINDLY GUIDE ME.

 

[b4bb4ge]

Your second method will provide a better phase noise if you are using the same architecture for your PLL in each PLL design. Due to the theoretical effects of frequency doubling when you double the frequency your phase noise will increase by 6 dB. You will only take a 3 to 4 dB increase by using a PLL at the higher frequency. What phase noise are you looking to achieve? There are several company's out there that make very low cost PLL's at 13.9GHz. I have had good results from Microwavetools and Hittite

 

[vfone]

Which approach is better, is a relative decision, even there is a 20*LOG(N) phase noise degradation.
Sometimes multiplying a very clean, low-phase-noise signal, can still produce signals with better phase noise than producing them directly at microwave frequencies. This is the reason that even today, frequency multiplication is the main option generating clean signals at microwave frequencies.

 

[abhijitrc]

But which is most widely used technique? Is it a better decision to use the second option of my earlier thread, since we have to generate a carrier frequency of 13.9GHz for first down conversion( Rf ~ 14.5GHz) , our receiver is FM based superhetrodyne, how phase noise effect the performance of the receiver???

 

[vfone]

You can get the answer (and set the limits) only after a system analysis, and see how your RF system is affected by the LO phase noise at various offsets from the carrier.
Usually FM receiver is affected by the wideband phase noise of the LO (far from the carrier, and not by the phase noise close by the carrier), but this is not a rule.

 

[tony_lth]

For FM receiver, the phase noise requirements are not strict. Hittite is enough for this, with or without multiplier are both ok.

 

[poorren]

Your second method will provide a better phase noise if you are using the same architecture for your PLL in each PLL design. Due to the theoretical effects of frequency doubling when you double the frequency your phase noise will increase by 6 dB. You will only take a 3 to 4 dB increase by using a PLL at the higher frequency. What phase noise are you looking to achieve? There are several company's out there that make very low cost PLL's at 13.9GHz. I have had good results from Microwavetools and Hittite

Why u state 'take a 3 to 4 dB increase by using a PLL at the higher frequency'? For PLL direct synthesis, the close-in phase noise is dominated by PLL's FOM, which you double the frequency, the increment of close-in phase noise should also increase 6dB.

 

[b4bb4ge]

Poorren,

The close in phase noise is dominated by they crystal that you are locking you PLL too and how well you can lock to that source. The close in phase noise is dominated in the case of a PLL by the PLL not being able to perfectly lock on the exact same point of the crystal every time so the signal has phase movement around what the PLL thinks is the same point that it saw last time on your reference. This is often why in PLL applications it asks that you lock to a square wave and not a sine wave (your phase noise will be much worse if you lock to a sine than a square). While I use a lot of PLL's I have never actually designed one but I do know that your phase noise is largely driven by how clean your source crystal is and how good your PLL can lock to it. Often if you use a nice trigger on your reference clock you can get better than 4dB degradation when doubling your frequency.

Here is a Berkeley paper that explains it much better than I do:
**broken link removed**

Good luck!

 

[biff44]

The phrase "active multiplier" sets off my alarm. It is theoretically true that a 13 GHz PLL should have the same phase noise as a 7 GHz PLL and X2. But in the real world, one usually gets a poor effective noise figure from an "active multiplier", and ends up with much more broadband noise at its output. If that is the case, you can end up self jamming your receiver with the transmitter's broadband noise. You need to do a carefuly system calculation to see if you can get away with it.

 

[D.A.(Tony)Stewart]

I see Analog.Devices. released a new part this year 13GHz PLL with fract N mode up to 110MHz mixer.

Phase noise Figure of Merit -222dBc/Hz

$8/ea 1k

https://www.analog.com/en/press-release/06_18_12_ADI_Debuts_Industrys_Highest_Performing/press.html