DPD will linearize PA, LMS should not be limiting factor in that respect. In band spurs should be investigated before we say that LMS can or can not be used. What output power are we looking for?

On 15/10/2012 09:13, Andrey Sviyazov wrote:
Since we decided to make version 3 (due to additions of šLMS thermosensors) then we can also add external Fref prescaler for PLL, no problems here.
I think ICPR is more important restriction.
Srdjan said that it doesn't studied too deeply, but on my opinion, really reachable maximum Tx power no more then 25 dBm (without DPD).
So, we can't use LMS for LTE without DPD or additional filtration (2nd Tx IF).
In other hand, we can implement it similar to UmSEL and with upconversion, of course, but high quality SAW filter required (all flatness) to keeping EVM as small as possible.

Best regards,
Andrey Sviyazov.



2012/10/14 Alexander Chemeris <alexander.chemeris@gmail.com>
Srdjan, thanks for the answers. This is enough for us at the moment.

On Sun, Oct 14, 2012 at 3:50 PM, Srdjan Milenkovic
<s.milenkovic@limemicro.com> wrote:
> Hi Alexander,
> Remaining questions are addressed below.
>
>
> On 13/10/2012 21:47, Alexander Chemeris 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?
>
> 2. Do you have any experience what maximum output power we could achieve
> with LMS and proper amplifiers, while still staying in the bounds of the LTE
> Standard? What would be the limiting factor for the further power increase?
>
> The limiting factor here would be absolute specs on ACPR, out of band spurs
> ... i.e. TX spectrum mask, expressed in dBm not in dBc. For example, you may
> meet <= -45dBc ACPR but on the other hand you can not inject noise into
> adjacent channel more than xdBm. LMS device is OK for 20-25dBm modulated
> output power. We can probably push it more however this is šnot tested so
> far.
>
>
>
> 3. Is there any issues using TDD mode in LMS6002D? We've been using onnly
> FDD mode so far and it would be great to know what issues could we expect
> when switching to TDD mode.
>
> TDD mode should be just fine. We measured around 20us TX<->RX switching
> time. We will probably need to reconfigure VCO supplies on UmTRX board to
> simplify switching control while keeping switching time at 20us. Lat us know
> when you are ready for such experiment.
>
>
>
> --
> Regards,
> Alexander Chemeris.
> CEO, Fairwaves LLC / ïïï õÍòÁÄÉÏ
> http://fairwaves.ru
>
>



--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ïïï õÍòÁÄÉÏ
http://fairwaves.ru