LMS TxLO noise

Andrey Sviyazov andrey.sviyazov at fairwaves.ru
Thu Jul 19 07:30:03 UTC 2012


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<http://code.google.com/p/umtrx/issues/list?can=1&q=&colspec=ID+Type+Status+Priority+Milestone+Owner+Summary+Modified&cells=tiles>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.
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