LMS TxLO noise

Andrey Sviyazov andrey.sviyazov at fairwaves.ru
Thu Jul 19 15:33:00 UTC 2012


Alexander.
I think that few pulses of LMS hardware reset (LMS_NRST-1 and LMS_NRST-2
pins) will be much easily than all registers checking.
BTW, are there reset pulses after power up or not?

Best regards,
Andrey Sviyazov.



2012/7/19 Alexander Chemeris <alexander.chemeris at gmail.com>

> Guys, please keep track of all LMS configuration values which are not
> set to default during power on and we'll add them to our manual
> initialization script.
>
> On Thu, Jul 19, 2012 at 6:56 PM, Andrey Sviyazov
> <andrey.sviyazov at fairwaves.ru> wrote:
> > Sergey.
> > I'll play around GPS power and RTC supply, thank you for your help.
> >
> > Thomas.
> > About r0x16 please be sure that sometimes it isn't set to default value
> > after power up (I saw it few times).
> > Also I think that possible those bad "power on reset" gave us unstable
> > result of LMS autocalibration.
> >
> > Best regards,
> > Andrey Sviyazov.
> >
> >
> >
> > 2012/7/19 sergey kostanbaev <sergey.kostanbaev at gmail.com>
> >>
> >> Which gives ~1.5khz cut-off, that's strange
> >>
> >> Also I'd check GPS VDD and AVDD nosies
> >>
> >>
> >> On Thu, Jul 19, 2012 at 6:41 PM, Andrey Sviyazov
> >> <andrey.sviyazov at fairwaves.ru> wrote:
> >>>
> >>> 1kOhm resistor and 0.1uF capacitor already exist between DAC and VC
> >>> input.
> >>> Of course I'll increase capacitance or resistance to be sure about VC
> >>> pin.
> >>>
> >>> Best regards,
> >>> Andrey Sviyazov.
> >>>
> >>>
> >>>
> >>> 2012/7/19 sergey kostanbaev <sergey.kostanbaev at gmail.com>
> >>>>
> >>>> No :) But it may cause.
> >>>>
> >>>> I'd check all the line from FPGA to DAC to VCTXCO because VC pin is
> >>>> really sensible to any noise.
> >>>>  - caused by power supply of DAC.
> >>>>  - output noise of DAC.
> >>>>  - algorithm of changing values
> >>>>
> >>>> At first I'd inspect VC pin at VCTXCO and try to filter it with
> cut-off
> >>>> frequency 1-0.1 Hz
> >>>>
> >>>>
> >>>> On Thu, Jul 19, 2012 at 6:29 PM, Andrey Sviyazov
> >>>> <andrey.sviyazov at fairwaves.ru> wrote:
> >>>>>
> >>>>> Sergey.
> >>>>> Is it really so frequently (32k/s updates at 1pps reference)?
> >>>>>
> >>>>> Best regards,
> >>>>> Andrey Sviyazov.
> >>>>>
> >>>>>
> >>>>>
> >>>>> 2012/7/19 sergey kostanbaev <sergey.kostanbaev at gmail.com>
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> On Thu, Jul 19, 2012 at 6:10 PM, Andrey Sviyazov
> >>>>>> <andrey.sviyazov at fairwaves.ru> wrote:
> >>>>>>>
> >>>>>>> Hi all.
> >>>>>>>
> >>>>>>> I've found spurs on the LO noise plot at  ~33kHz and ~66kHz offset
> >>>>>>> when GPS antenna used and position locked.
> >>>>>>> This spurs begin grow up when GPS just near to lock position and
> >>>>>>> after locking spurs stopped to grow as you can see at picture.
> >>>>>>> If thereafter GPS disconnected then noise coming back to normal
> plot.
> >>>>>>> I think that it is result of 32768Hz clock in the GPS module
> EB-230,
> >>>>>>> but can't understant how it can impact to 26MHz clock or VCO.
> >>>>>>
> >>>>>>
> >>>>>> As another idea it can be caused by continues GPS correction lead to
> >>>>>> DAC changes to the VCTXCO.
> >>>>>>
> >>>>>>>
> >>>>>>> Please tell me something who know.
> >>>>>>>
> >>>>>>> Thomas.
> >>>>>>> Was GPS antenna connected when noise measured like on the picture
> >>>>>>> which you sent us (also attached here)?
> >>>>>>> I would to know because of anomal peak near to 30kHz offset too.
> >>>>>>>
> >>>>>>> Best regards,
> >>>>>>> Andrey Sviyazov.
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> 2012/7/19 Andrey Sviyazov <andrey.sviyazov at fairwaves.ru>
> >>>>>>>>
> >>>>>>>> Sorry, that was meant to be sent to the mailing list :)
> >>>>>>>>
> >>>>>>>> Best regards,
> >>>>>>>> Andrey Sviyazov.
> >>>>>>>>
> >>>>>>>> ---------- Forwarded message ----------
> >>>>>>>> From: Andrey Sviyazov <andreysviyaz at gmail.com>
> >>>>>>>> Date: 2012/7/18
> >>>>>>>> Subject: LMS TxLO noise
> >>>>>>>>
> >>>>>>>> Hi Thomas.
> >>>>>>>>
> >>>>>>>> Here forwarded my last e-mail with noise plots when I stopped work
> >>>>>>>> around it at first time, please see below.
> >>>>>>>>
> >>>>>>>> Please try to play around Tx PLL charge pump current (register
> 0x16)
> >>>>>>>> for better RMS phase stability.
> >>>>>>>> I think we should reach 1 degree or below.
> >>>>>>>>
> >>>>>>>> Alexander gave me the second UmTRX board and after checking and
> >>>>>>>> fixing all known hardware issues I've got roughly the same LO
> noise plot.
> >>>>>>>> Possible Robin had no time to fixing all of our issues, so check
> >>>>>>>> them all please.
> >>>>>>>> And also check please what type of TCXO installed on your board.
> >>>>>>>>
> >>>>>>>> Best regards,
> >>>>>>>> Andrey Sviyazov.
> >>>>>>>>
> >>>>>>>> ---------- Forwarded message ----------
> >>>>>>>> From: Andrey Sviyazov <andreysviyaz at gmail.com>
> >>>>>>>> Date: 2012/4/13
> >>>>>>>> Subject: Re: LMS TxLO noise
> >>>>>>>>
> >>>>>>>> Hi all.
> >>>>>>>>
> >>>>>>>> There is progress with LMS PLL :)
> >>>>>>>> Pictures are attached here.
> >>>>>>>> t was discovered that 80 kHz spurs come from Ethernet, or rather
> >>>>>>>> from the ET1011.
> >>>>>>>> I unknowingly put the choke between transistor of 1V regulator and
> >>>>>>>> analog power 1V.
> >>>>>>>> As a result, the regulator has become unstable and oscillated 80
> kHz
> >>>>>>>> with amplitude of 200 mV, which climbed into the LMS PLL.
> >>>>>>>> To correct this problem L46 should be replaced by jumper on all
> alfa
> >>>>>>>> version PCB's.
> >>>>>>>>
> >>>>>>>> Also I just played with current in the PLL loop, shown on the
> >>>>>>>> picture for clarity.
> >>>>>>>> Proved to be the optimal current 1,9 mA (you should write 0x93 in
> >>>>>>>> the register of 0x16).
> >>>>>>>> But, I think, for the RxPLL will be better use of the current 2.4
> >>>>>>>> mA, because the nearest noises more important for Rx (you should
> write 0x98
> >>>>>>>> in the register 0x26).
> >>>>>>>>
> >>>>>>>> Best regards,
> >>>>>>>> Andrey Sviyazov.
> >>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>
> >>>>
> >>>
> >>
> >
>
>
>
> --
> Regards,
> Alexander Chemeris.
> CEO, Fairwaves LLC / ООО УмРадио
> http://fairwaves.ru
>
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