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 

"Johnson Liuis" <gpsabove@yahoo.com> wrote in message 
news:d9pdt7$fh8$1@domitilla.aioe.org...
> 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.

I remember that was mentioned somewhere in uBlox documentation. Try 
www.ublox.com 

Hello Johnson,

> 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. ...

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

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


"Aleksandar Kovacevic" <alexx@fly.srk.fer.haer> wrote in message 
news:d9per3$f09$1@ss405.t-com.hr...
> "Johnson Liuis" <gpsabove@yahoo.com> wrote in message 
> news:d9pdt7$fh8$1@domitilla.aioe.org...
>> 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.
>
> I remember that was mentioned somewhere in uBlox documentation. Try 
> www.ublox.com
> 

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



"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message 
news:0ofwe.608$j04.567@newssvr21.news.prodigy.com...
> Hello Johnson,
>
>> 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. ...
>
> 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 

"Johnson Liuis" <gpsabove@yahoo.com> wrote in message 
news:d9smoo$ghg$2@domitilla.aioe.org...
> 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?

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

Hello Johnson,

> 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?

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