Design and characterization of an integrated passive balun for quad band GSM applications

In today´s mobile phone application, more functionality and integration are expected in the front end RF sections, which include transceiver module, PA module, power management, digital processors, and others. In addition, package and module size, and form factor become an important aspect for these handhold applications. In this paper, we report the successful design of a smaller size, low loss, and cost effective dual balun for cell, EGSM, DCS & PCS bands (quad band) GSM/EDGE applications. The designed balun can be implemented onto a transceiver module´s transmit (Tx) path. The integrated passive device (IPD) baluns show superior performance to commercially available discrete SMT baluns, with a much smaller size. Viable packaging approach is also explored to keep the cost and size low with hardly any penalty to electrical performance. The final smaller size balun design reduces die size, and hence die cost without sacrificing the performance. The size of the quad band GSM balun is 1.2mmtimes1.4mm. Measured insertion loss (IL) and return loss (RL) of the balun for low band - Tx and high band - Tx show IL < 0.8 dB, RL < 12dB. Measured amplitude & phase balance for low band - Tx show amplitude balance < plusmn 0.02 dB, and phase balance < plusmn 0.1 deg. For high band - Tx, amplitude balance < plusmn 0.03 dB, phase balance < plusmn 0.2 deg