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Srdjan Milenkovic s.milenkovic at limemicro.comHi Alexander, 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. LMS is quite robust regarding temperature change. For example, PLL will stay locked within +/-20 deg C from the tuning point. 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. 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. Best regards, Srdjan Dr Srdjan Milenkovic On 28/07/2012 03:15, Alexander Chemeris wrote: > 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 > <s.milenkovic at limemicro.com> wrote: >> 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 >> <alexander.chemeris at gmail.com> wrote: >> >> On Thu, Jul 26, 2012 at 3:31 PM, Srdjan Milenkovic >> <s.milenkovic at limemicro.com> 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 >> http://fairwaves.ru >> >> > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/umtrx/attachments/20120728/8e8ea55e/attachment.htm> -------------- next part -------------- A non-text attachment was scrubbed... Name: afgfgeah.png Type: image/png Size: 22003 bytes Desc: not available URL: <http://lists.osmocom.org/pipermail/umtrx/attachments/20120728/8e8ea55e/attachment.png>