LMS6002D support of LTE

John Orlando john at epiqsolutions.com
Sat Oct 13 22:24:02 UTC 2012


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.

>>  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.

-- 
John Orlando
CEO/System Architect
Epiq Solutions
http://www.epiqsolutions.com




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