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Design >> RF Design >> RSSI
https://designers-guide.org/forum/YaBB.pl?num=1207571471

Message started by aaron_do on Apr 7^th, 2008, 5:31am

Title: RSSI
Post by aaron_do on Apr 7^th, 2008, 5:31am

Hi all,

what kind of accuracy do we normally see in the RSSI? My thinking is that it is difficult to properly define the receivers gain since the LNA and mixer gain an easily vary by a few dB. You can make a very accurate channel fitler and VGA i guess...

thanks,
Aaron

Title: Re: RSSI
Post by pancho_hideboo on Apr 7^th, 2008, 5:52am

aaron_do wrote on Apr 7^th, 2008, 5:31am:

Hi all,
what kind of accuracy do we normally see in the RSSI? My thinking is that it is difficult to properly define the receivers gain since the LNA and mixer gain an easily vary by a few dB. You can make a very accurate channel fitler and VGA i guess...
thanks,
Aaron

It depends on required input dynamic range and calibration's accuracy. For example, use compensation table determined by calibration procedure.

If you adopt complicated calibration over temperature, supply voltage and input frequency,
accuracy of less than +/-1.5dB is very possible.
Here you need temperature sensor, ADC and EEPROM, etc.

Title: Re: RSSI
Post by loose-electron on Apr 7^th, 2008, 12:57pm

this is the reason every cell phone on the planet goes thru calibration and storage of some tweak values that are unique to the chip set in the phone. Not able to design around it, or at least it hasnt been done yet.

Jerry

Title: Re: RSSI
Post by aaron_do on Apr 8^th, 2008, 3:31am

Hi,

thanks for the replies. I took pancho_hideboo's reply to mean automatic calibration during operation. Are you, Jerry, talking about calibration of the chip itself (for instance trimming of resistors)? Also, why would you need such accuracy in the RSSI? I understand you may want to limit the amount of power transmitted to and from the cell phone, but to whay accuracy?

thanks,
Aaron

Title: Re: RSSI
Post by pancho_hideboo on Apr 8^th, 2008, 3:40am

aaron_do wrote on Apr 8^th, 2008, 3:31am:

Also, why would you need such accuracy in the RSSI? I understand you may want to limit the amount of power transmitted to and from the cell phone, but to whay accuracy?

For example, very high accurate transmit power control is needed in CDMA application.

Title: Re: RSSI
Post by didac on Apr 8^th, 2008, 3:42am

Hi,
I think that it depends on the system, I don't think that it's needed the same accuracy in a Bluetooth like system(where you use RSSI for power saving) than in a mobile phone system(that control cell handover or cell breathing in the UMTS system).
Hope it helps,

Title: Re: RSSI
Post by didac on Apr 8^th, 2008, 3:43am

yups... pancho was faster than me writing...

Title: Re: RSSI
Post by loose-electron on Apr 8^th, 2008, 3:24pm

adjustment values are a stored numeric, dumped into flash in a cell phone, not used to trim the chip. Essentially adjustments done in Software (32dbm out is setting 11111 on one phone and 11110 on another kind of thinking)

All phones (CDMA and GSM) need to adjust power output, thats inherent to the system needs.
Accuracy required is within 1-2 db if I remember correctly.

jerry