A Miniaturized Marchand Balun in CMOS With Improved Balance for Millimeter-Wave Applications

The analysis and design of a millimeter-wave passive balun on silicon substrate with small size and good balance is presented. The reason for the imbalance of the balun is analyzed and a novel method using two grounded T bars beneath the coupled lines to tune the balance is proposed. The balun was fabricated in a 65 nm CMOS process, by using broadside coupled lines with small separation, the length of balun is reduced, resulting in a size of only 0.01 mm². In the 57-67 GHz band, the measured amplitude imbalance is less than 0.5 dB and the phase imbalance is less than 1 °. This method for optimizing the imbalance of balun is efficient and it does not increase the size of balun.