RF Switcher and Current Monitor Sample

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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



Re: RF Switcher and Current Monitor Sample
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I remember that was mentioned somewhere in uBlox documentation. Try
www.ublox.com



Re: RF Switcher and Current Monitor Sample
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


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Re: RF Switcher and Current Monitor Sample
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Sorry, not my area. I ran into it accidentally :-)



Re: RF Switcher and Current Monitor Sample
Hello Johnson,

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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

http://www.analogconsultants.com

Re: RF Switcher and Current Monitor Sample

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



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Re: RF Switcher and Current Monitor Sample
Hello Johnson,

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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

http://www.analogconsultants.com

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