DC Offset vs temperature

Robin Coxe coxe at close-haul.com
Sat Jul 28 15:44:18 UTC 2012


It might make sense to do some thermal cycle tests with a few temperature
sensor breakout boards like this one:
https://www.sparkfun.com/products/9418


On Sat, Jul 28, 2012 at 11:17 AM, Andrey Sviyazov <andreysviyaz at gmail.com>wrote:

> Hi Srdjan.
>
> Can we measure of all important for us instabilities of calibrations vs
> temperature and then write it to EEPROM for mass production?
> I mean, do you have information about repeatability of curves (laws) of
> deg C instabilities for chips with same and different date codes of
> manufacture?
>
> Also, how near should be temperature sensor to the LSM chip?
> I mean, can be used averaged relative temperature of the housing heatsink,
> with known gradient, of course?
> Please recommend us measure method, even if we need personal temperature
> sensor for each onboard LMS's.
>
> Best regards,
> Andrey Sviyazov.
>
>
>
> 2012/7/28 Srdjan Milenkovic <s.milenkovic at limemicro.com>
>
>>  Hi 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
>>
>>
>>
>>
>>
>>  ** **
>>
>>  ****
>> 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> <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> <alexander.chemeris at gmail.com> wrote:
>>
>> On Thu, Jul 26, 2012 at 3:31 PM, Srdjan Milenkovic<s.milenkovic at limemicro.com> <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 УмРадиоhttp://fairwaves.ru
>>
>>
>>
>


-- 
Robin Coxe  |  Close-Haul Communications, Inc.  |  Boston, MA
+1-617-470-8825
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