External antenna connected detection circuit

Hans Christian Glittenberg

Other Parts Discussed in Thread: CC1190, LMV225

Hi,

the maximum allowable input power to the cc112x is 10 dBm. When an antenna is not connected due to an end-user disconnection, I guess the reflected power could possibly destroy the internal PA. This is scenario is probably more valid when an external PA is used.

I know one could use a directional coupler with a log amplifier in order to detect the reflected power level and give a warning that the antenna is disconnected. However, I was wondering if there is a simpler solution that could be employed to detect if an antenna is disconnected? Some antennas do have a resistor with high value connected to ground inside the antenna, this is great for simple detection. But unfortunately not all antennas do have this feature...

Anyone who has any insight to this issue?

over 10 years ago

0 PM over 10 years ago

TI__Mastermind 27145 points

Hi,

It seems you are concerned with an unmatched (open ended) external PA would damage CC112x due to the reflected power from the PA.

The reflected power reaching from the output of the PA to the input is very less due to an isolation from the output to the input. So, the reflected power won't destroy CC112x.

Thanks,

0 Hans Christian Glittenberg over 10 years ago in reply to PM

Expert 2235 points

Hi,

OK, that is good to know, thank you. Do you know what is the case with cc1190? Would some sort of detector be required for this PA? Or external isolator, circulator etc?

Regards

0 PM over 10 years ago in reply to Hans Christian Glittenberg

TI__Mastermind 27145 points

Hi,

You don't need any VSWR protection circuit for CC1190. So, no need to use any curculator/Isolator circuit. Just follow our reference design.

Some PA s require VSWR protection circuit, otherwise they fail.

Thanks,

0 RGW over 10 years ago in reply to PM

TI__Mastermind 31610 points

Hi,

Check out app note AN112 (http://www.ti.com/lit/pdf/swra393), figure 18. If you want to detect if there is an antenna connected then the current could be monitored.

Regards, Richard

0 Hans Christian Glittenberg over 10 years ago in reply to RGW

Expert 2235 points

Hi Richard,

that's a good idea! thank you. I also did some simulations with a power detector: http://www.ti.com/product/lmv225 . One can utilize the fact that standing waves will appear on the TL line to the antenna connector. Even better, if there is a quarter wavelength from the tap-point to the antenna itself, there will be a massive change in readout due to quarter wave transformer open->short etc. This does not require a directional coupler.

Regards

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External antenna connected detection circuit