On chip balun single ended to differential

[analog_ambi]

On chip balun for single ended to diff
Today at 12:14pm Quote Modify
Hi,
I am using a balun to convert single ended signal (from signal generator) to differential (onchip).

1. Is it necessary to ground the center tap of secondary? I am AC coupling the differential.

2. Since sig gen has 50 ohm impedance i have put a 50 ohm in parallel with primary.

 

[vfone]

In this situation the center tap of the balun should be connected to the ground. Either, direct connection or using a decoupling capacitor.

 

[tony_lth]

There is no need for the 50 ohms.

 

[analog_ambi]

But the sig gen will have 50 ohm resistance right? Is it not required to match?

 

[BigBoss]

-50 Ohm is required because it creates a frequency independent but lossy termination, NOT matching.Termination is also important, otherwise the reflected wave through generator will impact the generator.( Protection,stability etc.)You can not really provide matching for all frequencies with a transformer winding, its impedance is variable in a wideband.
-If "Pseudo Ground" point is connected to real GND, the transformer will supply real differential with zero mean value.Otherwise the signals may have assymetric waveform because of nonideal windings and couplings.

 

[analog_ambi]

Thanks BigBoss!!