I am again involved an RF design and I am unsure on how to connect up the Balun, minicircuits application note suggests that it is dependant on the polarity/phase of the input signals (which makes sense) but I have seen conflicting implementations of the Balun in evaluation boards from analog devices.
The app note suggests a configuration like such:
{**+** ---- [P* S] --- **Out**}
{**-** ---- [P S*] --- **Gnd**}
In order to achieve an output which is twice that of the input signal, and this is indeed my aim as I am using a frequency synthesizer with complementary RF outputs.
In the evaluation board I have seen:
{**+** ---- [P S] --- **Out**}
{**-** ---- [P* S*] --- **Gnd**}
This is also complicated by the fact I am using a config K balun (Tri-Filar) from minicircuits, which also states in the datasheet that the primary port is/should be connected to ground.
So my question is, does the way in which I connect my signals to the Balun matter (either Primary or Primary*)?
and should I be concerned about the config K datasheet telling me to connect the primary to ground?
Many thanks
Best Answer
One instance wires the thing as a balun (Common mode choke), the second case is a transformer...
Usually you see the transformer configuration used up to maybe a 150MHz or so, with the balun configuration employed once things get fast, but your best approach is probably to try it both ways and see what the network analyser has to say.
The transformer configuration can be useful when DC isolation is desired, the balun when the non ideal nature of VHF transformers becomes a problem.