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RF Switcher and Current Monitor Sample

Hi there,

I am currently working on a GPS Receiver that is able to support both internal and external antenna. I would like the system to detect the external antenna and switch to the external antenna automatically. I remembered I once read a sampe from a magazine that required a RF switcher and a Current Shunt Monitor (like INA138) to detect the current, but I forgoty where it was. Could anybody provide me some information for this type of circuits design using RF switcher and Current Monitor? Any recommendation, suggestion, warning, or tips are highly appreciated.

Thanks in advance.

Johnson

Reply to
Johnson Liuis
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I remember that was mentioned somewhere in uBlox documentation. Try

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Reply to
Aleksandar Kovacevic

Hello Johnson,

The classical approach would be to use PIN diodes to switch between the antennas. At regular intervals your circuitry (behind the receiver output) could switch to the external antenna and make a decision based on signal strength. The decision could, for example, be contingent on seeing a signal at all or you could decide based upon which antenna delivers the best signal.

Regards, Joerg

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Reply to
Joerg

Thank you very much, Aleksandar,

I found out the document you mentioned at the uBlox website (under Service). I still prefer a current monitor plus a RF switch solution, since I am using

2 active antennas with almost the same gain. Could you please recommend me a few current shunt monitor (want bigger output current compared to INA138 with 100uA max output when the differential input voltage is 0.5V), and a few RF switch (want smaller DC power consumption than SKY13268-344 with 100uA max. consumption) as well?

John

Reply to
Johnson Liuis

Thanks a lot, Joerg,

I thought about your idea about using PIN diodes by making a decision based on signal strength. Definitely it is a good idea and will work. I possibly can devote one pin from the DSP inside of the GPS receiver to control the RF circuit. However, I appreciate a pure "hardware" solution and an easy one, better inside of the RF circuit itself. For this reason, I still prefer a current monitor plus a RF switch solution, and I am using 2 active antennas with almost the same gain. Could you please recommend me a few current shunt monitor (want bigger output current compared to INA138 with 100uA max output when the differential input voltage is 0.5V), and a few RF switch (want lower DC power consumption than SKY13268-344 with 100uA max. consumption) if you are familiar with these parts?

John

Reply to
Johnson Liuis

Sorry, not my area. I ran into it accidentally :-)

Reply to
Aleksandar Kovacevic

Hello Johnson,

Isn't the INA138 just a current sensor for the automotive world? What are you trying to monitor with it?

As for the RF switch I normally use PIN diodes so I am not too familiar with what's out there in terms of pHEMT. Look at Anadigics AWS5518, AWS5523 or some other new ones. Then there is the ADG series but you probably would need two. DC leakage seems really low on these though.

Regards, Joerg

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Reply to
Joerg

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