15 Oct
2012
15 Oct
'12
4:13 a.m.
Since we decided to make version 3 (due to additions of LMS 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(a)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(a)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 not 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 / ООО УмРадио
http://fairwaves.ru
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
http://fairwaves.ru