Yas Anda

In many communication systems, narrowband solutions are acceptable due to the reasonable fractional bandwidth requirements. Figure 1c presents a lumped element latticebalun design comprising lowpass and highpass filter networks that provide 180-degree phase difference between the two outputs. The filter polynomials are selected such that the frequency at which the 180degree phase difference is achieved corresponds to a half power 3dB magnitude response. This provides an equal split of the unbalanced input signal power, resulting in low insertion loss and excellent magnitude balance. The 3pole lattice balun design offers 20 percent fractional bandwidth with 1dB or better amplitude balance. Higher-order designs that can feasibly increase the useful fractional bandwidth are possible, but in practice they result in greater insertion loss and thus become unattractive when compared to wire-wound balun-transformer implementations. The main tradeoffs in selecting a lattice balun solution are the number of lumped elements required, the necessary bandwidth of operation, and the actual implementation issues that arise due to component values and circuit layout parasiticsA transformer has primary- and secondary coils. The two coils are DC isolated, and the secondary coil may or may not offer multiple taps. The taps on the secondary can function as return paths in applications such power transformers where multiple loads must be driven, or for feeding DC bias through a center tapa common practice in RF circuit interfacing. A transmission-line balun, Figure 1b, presents a DC connection between primary and secondary ports, and does not typically provide multiple secondary signal taps. This can be problematic in designs where the output signals need to be level shifted to a different common-mode level. External ACcoupling caps and bias chokes may be required if a common-mode level translation is required when using a transmission-line balun.