Fully Embedded 2.4GHz LC-Balun into Organic Package Substrate with Series Resonant Tank Circuit

In this paper, fully embedded lattice type LC-balun into an organic package substrate has been designed, fabricated, and characterized for low cost and small size WLAN and Bluetooth applications. In order to improve the performance characteristics of the balun, two approaches are performed. First, LC series resonant tank is newly applied at the low pass filter circuit of the conventional lattice type LC balun circuit topology. Second, the quality factors of these inductors and capacitors are maximized by using vertically stacked circular geometry and BTO high DK film. The size of the fabricated balun is significantly reduced, an area of 2.7 mmtimes2.5 mmtimes0.66 mm (height). It has the insertion loss of -0.7 dB, return loss of 21 dB, phase imbalance of 5 degree, and frequency band width ranged from 2.35 GHz to 2.55 GHz. The fabricated balun is smallest and first fully embedded one into the organic package substrate. It is promising for various RF SOP products with multi functionalities, small size, and low cost.