A silicon monolithic spiral transmission line balun with symmetrical design

In this work, a spiral transmission line balun has been fabricated on a hig h resistivity silicon substrate. The Marchand-type balun has been designed to have the same physical common ground points for the output transmission lines, which eliminates imbalance due to potential difference at the ground , Return loss is better than 17 dB in the frequency band of 1.6-1.1 GHz, es pecially 39 dB around 1.9 GHz, The amplitude imbalance is less than 0.3 dB throughout the bandwidth. The phase departure fi om 180 degrees is less tha n 2 degrees over the frequency range of 1.6-2.6 GHz. The balun is suitable for MMIC application.