DC Offset vs temperature

Alexander Chemeris alexander.chemeris at gmail.com
Sat Jul 28 02:15:57 UTC 2012

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

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

Alexander Chemeris.
CEO, Fairwaves LLC / ООО УмРадио

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