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very close-in phase noise generation (Read 40 times)
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very close-in phase noise generation
Jun 18th, 2003, 7:05pm
 
Hi, all,

I've designed a frequency synthesizer with integrated VCO (around 2GHz). I got the following phase noise (PN) performance in the actual measurements (agilent 4352 vco pll tester).

1K -65dBc/Hz
10K -80dBc/Hz
100K -100dBc/Hz
600K -120dBc/Hz

A clean crystal (fox 4106 44MHz) was used as the reference. The PLL type is integer. Phase detector update frequency is around 1MHz and the loop filter is off-chip (100KHz 3-dB bandwidth). The VDD's have been properly decoupled from GND with big caps.

As shown in the list, the phase noise @ 10KHz and beyong is decent. However, the phase @1K and below is unaccepable. This affects the integrated phase error (RMS) a lot.

As we know, usually the in-band PN curve is flat. However, I did see a flat curve, it is inceasing as frequency offset decrease from 1K to 100Hz.  I am wondering what caused this kind of high very-close-in-band phase noise and if there is any way to reduce it.

Any suggestions are appreciated. Thanks.

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Re: very close-in phase noise generation
Reply #1 - Jun 21st, 2003, 11:15am
 
OK. After a week's struggle with the close-in phase noise, I finally figured it out by myself.  :)

The problem of the close-in phase noise (1K and below) was caused by a lousy signal generator I used for reference of the 4352 VCO/PLL tester. When I switched to a better/newer siggen, Every problem was solved. I am now having a PN of -80~-90 @1K offset for in-band phase noise.

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