Knowledge Base

Single tie vs. rf switch (SX1261)?

Semtech uses an rf switch in the for RX/TX.
But in the 434MHz ref. design there is single tie antenna connection.
What are the pro's/con's (TCXO is mandatory for us)?
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The antenna switch allows different tuning for RX and TX path, so it gives an average gain of 2 db over single tie.

Olivier, thx.
2dB is a lot, so it make sense to consider the switch.

But: in case of battery driven modules, each uA counts. The switch is between 3-10uA.
Can I use DIO3 VDD-switching for TCXO and apply it to the switch VDD too?
Or do I oversee any possible side effects like switch ramp-up time or RX sniff modes where perhaps DIO3 isn't active?

best regards
I'm afraid it won't work, unless you are actually using a TCXO, because the XOSC would be turned on. Otherwise OK!
Just to make sure I've got you right:
we will use a TCXO and we will use a switch.

I want to activate both device VDD's using DIO3. There is no side effect/pitfall doing so (like RX sniff modes where SX126x is in sleep mode waiting for a signal, which never arise because the switch is turned off 😊 )


although I have not tested that, I believe this will work. The TCXO is turned ON for any active state (everything but Sleep), and therefore it will bias the switch, no issue (assuming the VDDs are compatible).

DIO3 at "1" with RxDutyCycle is integrated, so this is OK


As explained in the previous message, the TCXO is automatically turned ON when the state requires it (Rx, Tx, etc.) - as long as you called the function SetDIO3AsTcxoCtrl before.

The enclosed screenshot is an example where the chip is in Rx duty cycle mode and shows how DIO3 and BUSY lines behave. You can see that each time the chip enters the Rx state (corresponding to BUSY line low), the TCXO has been previously turned ON thanks to DIO3. The delay is the one you defined in the call to SetDIO3AsTcxoCtrl.

So, as long as your RF switch does not draw too much current in active mode, you can use DIO3 to power and control it.

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