Ceramics: the platform for duplexers and frontend-modules

In the last few years a significant trend from singleband to multiband applications has been observed, especially evident on GSM based phones. Four years ago singleband phones were standard. Today they have been fully substituted by dualband phones even for low end applications, and tripleband handsets for the high end market. In the near future quadband including GSM 850 will be established on the market. Adding third generation services to the existing second generation phones will lead to even more,complex systems. This continuing move towards higher functionality and increased complexity of the antenna interface is in contradiction to the requirements for smaller size, shorter development, cycles as well as cost and component count reduction. These objectives can only be met by a new level of integration of discrete passive and active components. Whereas the digital part is already highly integrated and of small size, the RF front-end section consists of a large number of components assembled on a printed circuit board. In the first step of integration the switching between different bands and modes was comprised in an antenna switch module (ASM). In the next step a front-end module (FEM) includes the surface acoustic wave filters (SAW filters) and dozens of matching elements. This development has been made possible by the utilization of LTCC technology (low temperature co-fired ceramics). Compared to FR4, LTCC is a low loss, high precision substrate allowing to integrate a large number of passive devices in a small volume. For example duplexers consisting of Tx and Rx bandpass filters for instance used in CW radio systems, or the UMTS/FDD mode, or diplexers for the 800 and 1900 MHz band allow with LTCC the smallest possible size. This paper covers the main issues of the design of LTCC based FEMs and duplexers. It focuses especially on the increase in overall system performance due to the reduction of external interfaces as well as optimization of internal interfaces in the RF chain.