LMS6002D support of LTE

Alexander Chemeris alexander.chemeris at gmail.com
Sun Oct 14 07:30:49 UTC 2012


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




More information about the UmTRX mailing list