LMS TxLO noise

Thomas Tsou thomastsou at gmail.com
Fri Jul 20 20:22:49 UTC 2012


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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[ttsou at ovid utils (umtrx)]$ ./umtrx_lms.py --lms 1 --lms-init
[ttsou at ovid utils (umtrx)]$ ./umtrx_lms.py --lms 1 --lms-tx-enable 1
[ttsou at ovid utils (umtrx)]$ ./umtrx_lms.py --lms 1 --reg 0x34 --data 0x3e
[ttsou at ovid utils (umtrx)]$ ./umtrx_lms.py --lms 1 --pll-ref-clock 26e6 --lpf-bandwidth-code 0x0f --lms-auto-calibration
LPF Tuning...
DC_REGVAL = 31
LPF Bandwidth Tuning...
FREQSEL=47 VCO_X=16 NINT=196 NFRACK=7743330
VOVCO[0]=2
VOVCO[1]=2
VOVCO[2]=2
VOVCO[3]=2
VOVCO[4]=2
VOVCO[5]=2
VOVCO[6]=2
VOVCO[7]=2
VOVCO[8]=2
VOVCO[9]=2
VOVCO[10]=2
VOVCO[11]=2
VOVCO[12]=2
VOVCO[13]=2
VOVCO[14]=2
VOVCO[15]=2
VOVCO[16]=2
VOVCO[17]=2
VOVCO[18]=2
VOVCO[19]=2
VOVCO[20]=2
VOVCO[21]=2
VOVCO[22]=2
VOVCO[23]=2
VOVCO[24]=2
VOVCO[25]=2
VOVCO[26]=2
VOVCO[27]=2
VOVCO[28]=2
VOVCO[29]=2
VOVCO[30]=2
VOVCO[31]=2
VOVCO[32]=2
VOVCO[33]=2
VOVCO[34]=2
VOVCO[35]=2
VOVCO[36]=2
VOVCO[37]=2
VOVCO[38]=2
VOVCO[39]=2
VOVCO[40]=2
VOVCO[41]=0
Norm
VOVCO[42]=0
VOVCO[43]=0
VOVCO[44]=0
VOVCO[45]=0
VOVCO[46]=0
VOVCO[47]=0
VOVCO[48]=0
VOVCO[49]=0
VOVCO[50]=0
VOVCO[51]=0
VOVCO[52]=1
Low
VOVCO[53]=1
VOVCO[54]=1
VOVCO[55]=1
VOVCO[56]=1
VOVCO[57]=1
VOVCO[58]=1
VOVCO[59]=1
VOVCO[60]=1
VOVCO[61]=1
VOVCO[62]=1
VOVCO[63]=1
START=41 STOP=51 SET=46
code = f f f
RCCAL = 7
Tx LPF DC calibration...
DC_REGVAL = 33
DC_REGVAL = 33
Rx LPF DC calibration...
Error: DC Offset Calibration does not converge!
RxVGA2 DC calibration...
Error: DC Offset Calibration does not converge!
[ttsouu at ovid utils (umtrx)]$
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