Implementation of the Front-End-Module with a Power Amplifier for Wireless LAN

Abstract

Recently, Wireless Local Area Network (W-LAN) market has been continuously growing in many filed and it become mature market. Therefore, a number of companies are researching and developing the W-LAN technology. Normally, W-LAN application is wildly used in the desktop computer, laptop computer, portable device, mobile phone, and so on. These application demands compact, small, low power consumption, slim, and many function in a module. These demands issue that a lot of components are integrated in a module. Low temperature co-fired ceramic (LTCC) continues to be attracted in wireless applications because it can implement a small, compact, and integrated module which embedding passive components by taking advantage of three-dimensional architecture. LTCC has high dielectric constant and low loss tangent that it has some benefits over other material substrates. The size of LTCC is shrunk after process of co-fired which makes some issues in design and implementation of LTCC. In spite of these disadvantages, many researches and companies have been researching and developing many passive components, RF modules, and front-end modules (FEM) by using the LTCC technology. IEEE 802.11 a/b/g as W-LAN standard has been allocated two frequency bands for 2.4 GHz 2.5 GHz (IEEE 802.11 b/g) and 5.15 GHz 5.85 GHz (IEEE 802.11 a). The frequency band of IEEE 802.11 b/g and of IEEE 802.11 a are called as low-band and high-band, respectively. The implemented W-LAN FEM coves low-band and high-band. It is composed of two matching circuits for low-band and high-band, two Tx low pass filters (LPFs) in order to reject 2nd harmonic frequency of a power amplifier module (PAM), two Rx band pass filters (BPFs) in order to reject interferers as blocker, a Rx diplexer to separate low-band from highband, a Tx diplexer, a single-pole-double-throw (SPDT) switch for sharing the antenna between the RX and TX paths , and a PAM for low-band and high-band as shown in fig.1. Two Tx LPFs, two matching circuits, Tx diplexer, two Rx BPFs, and Rx diplexer are embedded in LTCC substrate. A DPDT IC and PAM IC are mounted on LTCC substrate. Embedded components are very sensitive to tolerance of LTCC and mutual coupling. A control of process LTCC and a layout of embedded components are important facts and are focused on being considered in design of a FEM. The design and layout are mainly discussed in this book. 14