Ulrich Bauernschmitt

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.

Concepts for RF Front-Ends for Multi-Mode, Multi-Band Cellular Phones

This paper describes front-end architectures of modern multi-mode, multi-band cellular phones and will discuss the requirements on RF filtering in such applications. Special focus will be on dual mode (GSM and WCDMA) cellular phones with four GSM and three WCDMA bands. On the one hand driven by forward integration - e.g., from PA function via transmit front-end to a fully integrated radio - on the other hand influenced by new requirements of 3G systems and the integration of complementary access, filtering components such as SAW and BAW filters have to solve several increased requirements simultaneously. New technologies are required to follow the demand of increased RF performance, reduced PCB area consumption and continuously decreasing component costs.

High selectivity IF SAW filters for CDMA mobile phones

The Z-path structure is a good choice for intermediate frequency SAW filters in highly miniaturized mobile phones. In order to achieve the dramatic size reduction of up to 70% compared to inline structures, the Z-path concept has been combined with the recursive filter design technique resulting in a recursive Z-path filter. One of the advantages of this structure is the multiple mechanisms which can be exploited to shape the passband and to achieve high selectivity. However, at frequencies above 100 MHz the selectivity of a Z-path filter on a chip of minimum size is affected by inductive as well as capacitive crosstalk between the input and the output transducer. To meet the rejection characteristics required in modern telecommunication systems, a novel method to improve the stopband performance of Z-path filters was developed. It allows for an independent cancellation of both the inductive and the capacitive crosstalk by balancing the net current flow to a transducer and by equalizing the effective coupling capacitance from the input to the output transducer. The finger-electrodes themselves remain unchanged and thus the electro-acoustical behaviour is not affected. CDMA-filters having a selectivity of more than 65 dB are presented. The new technique is applied to filters for the CDMA-800 system at 128.1 MHz on quartz in a 13/spl times/6.5 mm/sup 2/ ceramic package. A CDMA-1900 filter at 210.38 MHz in a 5/spl times/5 mm/sup 2/ ceramic package is also presented.