A high input impedance magnetic balun/transformer having a phase balancing network (PBN) and method of operating. The balun is fully configurable and trimmable post fabrication using independently adjustable resistive and reactive parts by changing the resistance of a programmed transistor, e.g., NMOS. Parallel connected legs each having a field effect transistors (FETs) that make up NMOS device alter the impedance at the balun output terminals. The ground terminal of a secondary winding or coil at an unbalanced, single-ended side is connected to a phase balancing network. The phase balancing network includes at least two parallel legs, each leg having a resistive element in the form of a transistor device and at least one leg including a capacitive element. The transistor device at a leg can be operated in a linear region to trim the resistance and capacitances at the unbalanced side in order to achieve proper phase balancing and amplitude matching.