An integrated stacked transformer with large inductance at 900MHz

An on-chip transformer is optimized to have a good performance at low frequency with large self-inductance. The ports of primary and secondary are in orthogonal direction so as to resist the large current though the center-tap in some applications. At the frequency of 900Mhz, the quality factor of the primary is 7.7 while the secondary is 3.3, both of which have inductance of 11.4nH. It can work as an balun between the differential power amplifier and the single-end antenna with a turn ratio 1:1.The transformer is implemented on the SMIC 0.13um RF 1P8M process.