Mux for RFID antenna signal

[F-Moura]

Hello guys!

How are you?

Well, I´m working with RFID from Texas Instruments.
I am starting a new project that I want use 2 antennas for the same electronic.
Can I use a mux between antenna and electronic?
What are the parameters that I need look for make a best choice about mux?

Tnx very much!

PS: My RFID signal have 134.2KHz with +5V.

 

[FvM]

The question would be easier to answer if you tell reader IC and circuit details. For the usual differential driver with series resonance capcacitor, it's essential to place the multiplexer directly at the reader pins, otherwise it must handle high voltage (50 to 100V) of the resonant circuit. The multiplexer shouldn't add much series resistance to the driver output impedance.

 

[F-Moura]

Hi FvM,

well, I use TMS3705, 400uH antenna with 3.6nF resonance capacitor.
I will buy a mux and test it, if all work well I post the circuit.

tnx very much

 

[FvM]

Driver output impedance is typically 7 ohm. To avoid reduction of reader field strength, the mux switch shouldn't have than 1 or 2 ohm series resistance. Provide separate capacitors for each reader coil and switch only one driver pin.

 

[F-Moura]

Hello,

no is easy choose the IC to work how switch.
At my study I see that need a dual bilateral switch, but I´m being limited by Operating Range.
For example, NLX2G66 from On Semi, have Ron<5 ohms (how my circuit have 4.2 ohms in series with antenna I can use it), but VCC is +1.5V to 5.5V.
The signal of the antenna is a wave of 0 to +25V with very low current.
I question myself if the NLX2G66 will cutoff the voltage peak or no.
What do you think??

 

[FvM]

The signal at ANT1/ANT2 pins is limited to the reader supply voltage 0/5V. I already suggested a circuit taking adavantage from this fact.