LMS6002D support of LTE

Robin Coxe coxe at close-haul.com
Sun Oct 14 04:18:16 UTC 2012


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<http://www.analog.com/en/rfif-components/pll-synthesizersvcos/adf4002/products/product.html#product-designtools-nav>

-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
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