Balun transformer, mounting structure of balun transformer, and electronic apparatus having built-in mounting structure

A balun transformer, comprising:

• first to fourth layer coils stacked in that order in respective layers and coupled together magnetically,
• wherein,
• each of the layer coils has a first end and second end, the first end being the innermost end of the coil,
• the first end of each coil of the first to fourth layer coils is grounded,
• the second and third layer coils are connected in parallel,
• an unbalanced signal can be input or output or both to or from, respectively a common terminal of the second and third layer coils,
• a first balanced signal can be input or output or both to or from, respectively, the second end of the first layer coil, and
• a second balanced signal can be input or output or both to or from, respectively, the second end of the fourth layer coil.