A transmission line transformer (TLT) and a device for delivering serial digital signals at relatively high rates which comprises four such TLTs is provided. Each TLT has a primary and secondary coils winded at the same direction around a common core. Each of the primary and secondary coils comprises two segments of wires. The four segments of wires are grouped to a bundle which is axially twisted, wherein this twisting is characterized by a predefined number of full rotations relative to the axis of the bundle per a unit length, measured along this axis.