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<div class="moz-cite-prefix">Hi Alexander,<br>
<br>
I understand. It is the same with WCDMA and other FDD modulation
standards, BTS can not stop transmitting/receiving. However, we
can not expect temperature to change from -40 to +85 deg C without
doing anything about it.<br>
<br>
LMS is quite robust regarding temperature change. For example, PLL
will stay locked within +/-20 deg C from the tuning point. <br>
<br>
The graph below shows DC/LO leakage calibration stability vs
temperature. Applications based on OFDM (LTE, WiMAX for example)
do not need to wary about DC/LO leakage recalibration as DC OFDM
carrier is not used. Other modulation schemes will have to take
care of this. If we define the spec of -60dBc LO leakage, the
graph below shows that LMS IC is OK within +/-10 deg C offset from
the calibration point.<br>
<br>
BTW, you do not need UmTRXv3 at the moment. You can build a small
board with temperature sensor alone and interface it back to
BB/FPGA.<br>
<br>
Best regards, Srdjan<br>
<br>
<br>
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On 28/07/2012 03:15, Alexander Chemeris wrote:<br>
</div>
<blockquote
cite="mid:CABmJbFV7NP9dwQkNk47vwx0g6ssVVU+VKGjoy1S7pVjRWQEWQQ@mail.gmail.com"
type="cite">
<pre wrap="">Hi Srdjan,
Thank you for the comment.
Unfortunately, we can't perform regular re-calibration, because a GSM
base station can't stop transmitting. This means we need a full blow
temperature sensor and this is a bad news, as we have to create
UmTRXv3 to add it. This is something you should definitely consider
for your next-gen chip - an embedded temperature sensor.
Do you know how sensitive those parameters are to a temperature? I.e.
should we calibrate adjust them every centigrade or every five
centigrade?
On Fri, Jul 27, 2012 at 6:28 PM, Srdjan Milenkovic
<a class="moz-txt-link-rfc2396E" href="mailto:s.milenkovic@limemicro.com"><s.milenkovic@limemicro.com></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hi Alexander,
As I mentioned before, IQ phase error is quite stable over temperature in
900/1800MHz region so let us put it aside. This can be tuned and fixed in
production.
On the other hand, DC offset and LO leakage are temperature dependent as one
would expect. However, they can be calibrated in the product as well not
just in the lab. You need just to trigger built in DC cal blocks and
optionally use RF loop back to further improve LO leakage. If you want to
avoid temperature sensor you have an option to do these calibrations
regularly, every 30min-1h for example. This should track the temperature
change without having the sensor on board.
Our other customers are using both approaches, with and without temperature
sensor, depending on application and spec. If they have on board temperature
sensor they are using it for multiple purpose such as monitoring BB, PA,
etc.
Best regards, Srdjan
On 26/07/2012 16:48, Alexander Chemeris wrote:
On Thu, Jul 26, 2012 at 4:37 PM, Alexander Chemeris
<a class="moz-txt-link-rfc2396E" href="mailto:alexander.chemeris@gmail.com"><alexander.chemeris@gmail.com></a> wrote:
On Thu, Jul 26, 2012 at 3:31 PM, Srdjan Milenkovic
<a class="moz-txt-link-rfc2396E" href="mailto:s.milenkovic@limemicro.com"><s.milenkovic@limemicro.com></a> wrote:
Combining Thomas's idea of DC recalibration and, if necessary, making
look
up table for IQ phase error correction vs temperature should put us in
good
position to meet the specs.
Well, AFAIK, LMS6002D doesn't have a temperature sensor built in and
this means we have to install an external one, which again increase
BoM cost. Is that's how this issue is solved by your other customers?
I wonder is there a way to solve this without introducing a
temperature compensation loop.
Let me clarify - DC offset re-calibration is (more or less) fine in
lab setup, but it's expensive to manufacture if we have to add
temperature sensors and put every unit into a temperature camera for
calibration.
--
Regards,
Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио
<a class="moz-txt-link-freetext" href="http://fairwaves.ru">http://fairwaves.ru</a>
</pre>
</blockquote>
<pre wrap="">
</pre>
</blockquote>
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