Fig. 1. Block diagram of proposed transformer-based balun splitter with isolation and matching characteristic.

Fig. 2. Physical composition of proposed transformer-based balun splitter，（a）cross-sectional view of implemented BiCMOS back-end process，（b）three-dimensional layout representation of the proposed balun.

Fig. 3. Electro-magnetic simulation result of capacitive loaded transformer balun.

Fig. 4. Schematic of isolation circuit for baluns，（a）conventional isolation circuit，（b）cascaded LHTL-cells replacing 180° transmission line，（c）proposed lumped isolation circuit

Fig. 5. Performance comparison between cascaded LHTL-cells and 180° transmission line

Fig. 6. Measurement setup and die photograph of designed balun splitter.

Fig. 7. Measurement results comparison of the fabricated balun splitter chip（a）isolation and return loss result from measurement and simulation，（b）insertion loss and imbalance result from measurement and simulation