LMS6002D support of LTE

Alexander Chemeris alexander.chemeris at gmail.com
Sat Oct 13 21:30:46 UTC 2012


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.

>  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.


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




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