LMS TxLO noise

Andrey Sviyazov andrey.sviyazov at fairwaves.ru
Fri Jul 20 21:33:40 UTC 2012


Hi Thomas.

First of all thank you very much.

And of course few questions:
1 why you use too small input signal to the analyser? I saw -120dBc/Hz @
1MHz offset.
2 do you test LO with small CP current?
3 I don't see now noise peak @ 30kHz. Do you change something?
4 can 4406 measuring noise plot with log freq?
5 what type of modulation you use now? I mean 1 sps or 2?

Best regards,
Andrey Sviyazov.
(Sent from my mobile client)
 21.07.2012 0:23 пользователь "Thomas Tsou" <thomastsou at gmail.com> написал:

> On Fri, Jul 20, 2012 at 1:14 PM, Andrey Sviyazov
> <andrey.sviyazov at fairwaves.ru> wrote:
> > Hi Thomas.
> >
> > I couldn't wait your reply and start to implement 10kHz BW of PLL.
> > You can find here two pictures with results.
> > First of all I found that PLL tuning algorithm doesn't work properly at
> low
> > PLL BW.
> > VCOCAP register (r0x19) should contain higher value at least for +3 units
> > (to make CAP lower), otherwise freq's above 950MHz never locked.
> > Note, that you should read and change register 0x19 after autotuning.
> > Second, you can see some noise difference for the 925MHz because of used
> > DIV=8 of  the VCO, instead of DIV=4 for 942 and 960MHz.
> > Third, you can see PLL noice dependance with the charge pump current
> > (r0x16).
> >
> > On the other two pictures you can find which components have to be
> changed.
> > Thomas, please make one more measure of LO noise and jitter at PLL
> BW=10kHz
> > by your instrument.
> > We need to know, is it real to reach modulation accuracy of 1.5 degrees
> RMS
> > or impossible, just because of LMS PLL have bigger jitter.
>
> Here are phase noise plots with following settings measured at 925 MHz
> and 945 MHz.
>
> --reg 0x16 --data 0x93
> --reg 0x26 --data 0x98
>
> Charge pump current had a definite effect as did changing the
> frequency. Measured on the E4406A, phase error is quite high. There
> are still other calibration issues, but phase noise is probably still
> a concern. I also still have errors with auto calibration.
>
> Note that USRP1 - with better phase noise - does not reach < 1.5
> degree error, but is close at < 2.0 degrees RMS.
>
> I'm currently going through the previous issues. If there is anything
> else I should examine or test, let me know.
>
>   Thomas
>
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