LMS6002D support of LTE

Alexander Chemeris alexander.chemeris at gmail.com
Sun Oct 14 03:54:49 UTC 2012


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




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