RF (GSM/CDMA) POWER DETECTION MODULE

EDAboard.com Forum Index -> RF, Microwave, Antennas and Optics -> RF (GSM/CDMA) POWER DETECTION MODULE

Author

Message

joshicn

Joined: 18 Sep 2009
Posts: 4
Location: India

28 Oct 2009 8:03 RF POWER DETECTION

I want to detect GSM/CDMA recieve power levels as low as -100 dbm. These are power levels recieved @ basestations.

I've seen circuits detecting power levels upto -40 or -50 dbm but below that its bit problematic.

Any suggestions about using particular DIODE or anything else is welcomed.

Thanks in Advance.

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

28 Oct 2009 9:53 RF POWER DETECTION

Only a calibrated receiver or spectrum analyzer can do.

vfone

Joined: 10 Oct 2001
Posts: 2329
Helped: 327

28 Oct 2009 10:03 Re: RF POWER DETECTION

Diode detectors have low sensitivity.
You can use one of the Analog Devices Log Detectors AD8313 or ADL5513, and place in front of them two or three MMICs from Minicircuits.

http://www.mini-circuits.com/products/amplifiers_monolithic.html

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

28 Oct 2009 10:29 Re: RF POWER DETECTION

Quote:

You can use one of the Analog Devices Log Detectors AD8313 or ADL5513, and place in front of them two or three MMICs from Minicircuits.

It can't work, unless you reduce the bandwidth considerably ( e.g. < 1 MHz). Otherwise the input referred noise power will be already higher than -100 dBm.

vfone

Joined: 10 Oct 2001
Posts: 2329
Helped: 327

28 Oct 2009 16:15 Re: RF POWER DETECTION

Is cheaper to buy a two bucks SAW filter, instead spending many thousands of dollars for a calibrated receiver, or a spectrum analyzer.

joshicn

Joined: 18 Sep 2009
Posts: 4
Location: India

29 Oct 2009 5:19 Re: RF (GSM/CDMA) POWER DETECTION MODULE

Unfortunately, bandwidth is 75Mhz, centered @ 1842.5 Mhz.

Such detections are common in Tower mount amplifiers. MMICs with inbuilt bypass are already available with Hettite, Avago, Toshiba, Freescale etc. But I've to do this with discreet components.

Is there any other way to bypass amplifier circuit when Rx signal power exceeds prescribed level ?

I'll try using MMICx as Vfone suggested.

vfone

Joined: 10 Oct 2001
Posts: 2329
Helped: 327

29 Oct 2009 9:55 Re: RF (GSM/CDMA) POWER DETECTION MODULE

You can use BGA728L7 from Infineon which has high and low gain mode (+15dB and -5dB).

http://www.infineon.com/dgdl/bga728l7.pdf?folderId=db3a30431ce5fb52011d23bc9bee187a&fileId=db3a30431ce5fb52011d23be3a3b187b

Beware that is specified for 100MHz to 1.7GHz frequency range but I use it successfully up to 2.1GHz.
The only issue for you could be the package.

Another option is to use a standard MMIC and an RF switch to shunt it for a through state (low gain). Check Infineon for parts. In this case is possible to need two RF switches in series to increase the OFF isolation, otherwise the MMIC could become unstable.

FvM

Joined: 22 Jan 2008
Posts: 5161
Helped: 767
Location: Bochum, Germany

29 Oct 2009 10:47 RF (GSM/CDMA) POWER DETECTION MODULE

You can expect a noise level of about -85 to -90 dBm with 75 MHz bandwidth, if this is acceptable, you can use a
wide band detector. Otherwise, it has to be frequency selective.

Google
AdSense
Google Adsense

29 Oct 2009 10:47 Ads

joshicn

Joined: 18 Sep 2009
Posts: 4
Location: India

29 Oct 2009 13:35 Re: RF (GSM/CDMA) POWER DETECTION MODULE

1) So what you are proposing is - amplifying the signal and then comparing it with some reference. ? I'll check said LNA, but it'll take some time.

Or shall i first amplify the signal through LNA to be bypassed and check its level and switch on the bypass path if necessary ?

Further, I dont think noise will b a problem as all I need to do is detect signal power level and provide bypass if its above certain level. Noise may be tolerated in this case as application needs simple comparison.

Thanks.