Transmission Line Transformers (TLT):

• Optimal Characteristic Impedance: $Z_0 = \sqrt{Z_{in} \cdot rac{Z_{out}}{N_{lines}}}$ depending on topology. Usually, $Z_0 = \sqrt{Z_{in} \cdot Z_{out}}$ for standard 1:4.
• Guanella (Current): Focuses on providing high common-mode choking impedance. Excellent bandwidth and balance.
• Ruthroff (Voltage): Uses bootstrap voltage addition. Tends to have less high-frequency bandwidth than Guanella due to phase delay.