RF power amplifier impedance matching width transformer balun

[goatmxj666]

Hello,

I am designing RF linear power amplifier with cadence virtuoso.

I want to use a transformer balun to match the output impedance of the PA to 50 ohms(L2). (transformer balun= L1, L2)

The given spec (Vdd, Pout, 50 ohms) determines the inductor(L1) value of the transformer connected to my PA.

For example, if my proper output impedance(L1) is 10 ohms, what are the parameters I need to optimize?

Am I need additional capacitor or inductor in my PA when I doing optimization process?

If I'm doing impedance matching with LC matching instead of balun, I can do load pull simulation to find the optimal L and C values.

So, if the L1 value is set to 10 ohms when using a balun, does this mean that no additional impedance matching is required?

Or do I need more circuitry to match the impedance between my PA and 10 ohms?

 

[BigBoss]

Primary side should have Optimum Output Impedance of the PA while the secondary is exihibiting 50 Ohm@ Center of the Operating Frequency. Optimization is not easy but possible.
Optimum Load Impedance must be found first for the PA then the Transformer can be designed.
Don't forget, primary and secondary sides are NOT independent. Therefore parametric EM simulation should be used to get a appropriate solution.

 

[goatmxj666]

Primary side should have Optimum Output Impedance of the PA while the secondary is exihibiting 50 Ohm@ Center of the Operating Frequency. Optimization is not easy but possible.
Optimum Load Impedance must be found first for the PA then the Transformer can be designed.
Don't forget, primary and secondary sides are NOT independent. Therefore parametric EM simulation should be used to get a appropriate solution.

So how do you compensate for the imaginary part not being matched when the real part is matched through the transformer? Do you add an inductor or capacitor to cancle the imaginary mismatch?

 

[FvM]

If the PA output impedance is 10 + j0 ohms, there's nothing to compensate.

10:50 ohms however can't be implemented as a transformer balun with useful number of turns, 4:9 is the nearest integer ratio.

 

[BigBoss]

So how do you compensate for the imaginary part not being matched when the real part is matched through the transformer? Do you add an inductor or capacitor to cancle the imaginary mismatch?

If the Optimum Load Impedance is Complex, there is a difficulty to implement. The PA would see Complex Optimum Impedance but Transformer cannot transform a Real Impedance to Complex one. Therefore you have to create a Transformer Real-to-Real but the at the end Load Impedance will have some reactive part and your mission is to reflect this part as Complex part of Optimum Load Impedance.\
It's Hard to do. A long tweak will be necessary.
First, try with Real Impedances at both side, if you're satisfied with result, go with it.