LMS6002D support of LTE

Alexander Chemeris alexander.chemeris at gmail.com
Sun Oct 14 07:47:25 UTC 2012


Hum, good idea for the very first try. We should try this out this week.

But I still want a normal TCXO/OCXO replacement for UmTRX to make it
easier to rework more UmTRX boards.

On Sun, Oct 14, 2012 at 7:35 AM, sergey kostanbaev
<sergey.kostanbaev at gmail.com> wrote:
> Just use our ClockTamer to see how it works :)
>
>
> On Sun, Oct 14, 2012 at 11:30 AM, Alexander Chemeris
> <alexander.chemeris at gmail.com> wrote:
>>
>> Hi Robin,
>>
>> Do you mean to use ADF4002 to double the frequency?
>>
>> Right now I want a simple solution - just replace the TCXO on UmTRX
>> from 26MHz to 61.44MHz and see how it works. Doubling the frequency
>> would require PCB rework and is possible for the next generation of
>> UmTRX only.
>>
>> On Sun, Oct 14, 2012 at 4:18 AM, Robin Coxe <coxe at close-haul.com> wrote:
>> > Something like the attached Taiten VCTCXO @ 30.72 MHz + ADF4002 Phase
>> > Detector/PLL synthesizer might work.  I have no idea how much the
>> > oscillator
>> > costs.  (The Pletronics oscillator on the UmTRX and the GAPfiller GSM900
>> > isn't available at this frequency.)
>> >
>> >
>> > http://www.analog.com/en/rfif-components/pll-synthesizersvcos/adf4002/products/product.html
>> >
>> > -Robin
>> >
>> > On Sat, Oct 13, 2012 at 11:54 PM, Alexander Chemeris
>> > <alexander.chemeris at gmail.com> wrote:
>> >>
>> >> John,
>> >>
>> >> On Sun, Oct 14, 2012 at 12:24 AM, John Orlando <john at epiqsolutions.com>
>> >> wrote:
>> >> > On Sat, Oct 13, 2012 at 4:30 PM, Alexander Chemeris
>> >> > <alexander.chemeris at gmail.com> wrote:
>> >> >> Hi John,
>> >> >>
>> >> >> On Sat, Oct 13, 2012 at 11:11 PM, John Orlando
>> >> >> <john at epiqsolutions.com>
>> >> >> wrote:
>> >> >>> On Sat, Oct 13, 2012 at 3:47 PM, Alexander Chemeris
>> >> >>> <alexander.chemeris at gmail.com> wrote:
>> >> >>>> Hi Srdjan,
>> >> >>>>
>> >> >>>> We're looking into re-purposing UmTRX for LTE and there a few
>> >> >>>> things
>> >> >>>> which
>> >> >>>> we need to understand better.
>> >> >>>>
>> >> >>>> 1. Is it possible to support 15MHz and 20MHz LTE channel
>> >> >>>> bandwidths?
>> >> >>>> To
>> >> >>>> achieve this we at least need to sample at 23.04Msps and 30.72Msps
>> >> >>>> respectively. LMS6002D datasheet specifies the maximum I/Q
>> >> >>>> samplerate
>> >> >>>> of
>> >> >>>> 14Msps, which is not enough. But at the same time, datasheet
>> >> >>>> claims
>> >> >>>> that ADC
>> >> >>>> and DAC are specified up to 50Msps. How does this fits together?
>> >> >>>
>> >> >>> Alexander,
>> >> >>> Can you provide a reference to where the datasheet calls out a max
>> >> >>> I/Q
>> >> >>> sample rate of 14 Msps?  The analog low pass filters support a max
>> >> >>> bandwidth of 14 MHz (which leads to 28 MHz RF bandwidth assuming
>> >> >>> zero-IF operation)...is this what you're referencing?
>> >> >>
>> >> >> The datasheet is not very clear on this topic. I'm referring to the
>> >> >> following line at the Table 1:
>> >> >> Baseband Bandwidth       14MHz
>> >> >>
>> >> >> Originally I read this line as "digital I/Q bus has limitation of
>> >> >> 14Msps" and this is what confuses me.
>> >> >
>> >> > Yes, this refers to the analog baseband filter bandwidth.
>> >>
>> >> Ok, thanks for the clarification.
>> >>
>> >> >>>  We run the A/D
>> >> >>> converters in the LMS6002d at sample rates greater than 14 Msps all
>> >> >>> the time, including 30.72 Msps.
>> >> >>
>> >> >> Just to be sure - do you mean you feed RX_CLK and TX_CLK of LMS6002D
>> >> >> with 61.44MHz clock? It's divided by 2 internally, so if you feed
>> >> >> them
>> >> >> with 30.72MHz clock you actually get only 15.36Msps out of LMS6002D.
>> >> >
>> >> > Correct, when running the A/D at 30.72 Msps, the RX_CLK signal needs
>> >> > to run at 61.44 MHz.
>> >>
>> >> Great!
>> >> In case you know a good 61.44 MHz oscillator with a reasonable price -
>> >> I would appreciate a pointer.
>> >>
>> >> --
>> >> Regards,
>> >> Alexander Chemeris.
>> >> CEO, Fairwaves LLC / ООО УмРадио
>> >> http://fairwaves.ru
>> >>
>> >
>> >
>> >
>> > --
>> > Robin Coxe  |  Close-Haul Communications, Inc.  |  Boston, MA
>> > +1-617-470-8825
>>
>>
>>
>> --
>> Regards,
>> Alexander Chemeris.
>> CEO, Fairwaves LLC / ООО УмРадио
>> http://fairwaves.ru
>>
>



-- 
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru




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