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 mm(2). 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.