Improving LMS6002 phase noise

Srdjan Milenkovic s.milenkovic at limemicro.com
Sat Jul 21 14:33:27 UTC 2012


Hi all,

As far as I am aware, you are currently discussing how to improve 
LMS6002 PLL phase noise. Below are some inputs from my side which may help.

Apart from playing with PLL registers we have two additional options.

1. Use clean TCXCO which provides 4 times higher reference followed by 
divide by 4 to generate PLL reference clock. Recently, we experimented 
with 30.72*4 MHz TCXCO. Dividing its output by 4 before going into LMS 
chip we have got improvement of 6dB in phase noise plateau region.

2. Current PLL loop filter has been designed to cover the whole LMS 
frequency range hence using kind of mid value for Kvco. We can customize 
the loop filter for a particular band. To do that we need to know 
frequency range China Mobile is looking for and reference clock you want 
to use (26MHz, 26*4/4MHz, ...). Please note that PLL reference clock 
does not need to be the same as system clock i.e. we can also use 
30.72MHz, 30.72*4/4MHz etc.

Best regards, Srdjan

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