Abstract: Transformer is a key device in radio frequency communication circuit, which can directly effect on the performance of the RF front-end circuit. However, there is not transformer in TSMC 0.13m RF CMOS mixed-signal process library. In order to solve this problem, an octagonal transformer which is applied in LTE/WiMAX is designed and fabricated by the analysis of all kinds of on-chip transformer performance, and the frequency-independent lumped-element equivalent circuit model and the parameter-extracted expressions are given. The measurement results show that L and Q have excellent agreement with the measured data from the frequency range of 0.1GHz to 10GHz, and coupling coefficient K is perfect. The successful design of the transformer will contribute to the development and application of 4G communication chips.