Design And Performance Of A UMTS Picocell Front-End Module

Introduction

The wireless market is expanding with significant growth likely to be in Wideband Code Division Multiple Access (W-CDMA). Universal Mobile Telecommunications System (UMTS) is the third-generation (3G) wireless communications standard that is capable of delivering voice and high-speed data using W-CDMA. The UMTS system offers a layered approach to coverage by utilizing macrocells (towers), microcells, picocells, and femtocells. Picocells are essentially mini base stations that deliver ~24 dBm power at the antenna. These products fill in coverage gaps and add capacity in high-traffic, high data rate areas. Described herein is a new front-end module for the UMTS/W-CDMA picocell market. The term "front-end module" refers to the portion of an RF transceiver that extends from the antenna to the mixers or local oscillator section. In addition, these front-end modules can also be utilized for UMTS repeaters.

The module essentially consists of a transmit (Tx) bandpass filter, a Tx power amplifier (PA), a duplexer, a receive (Rx) low-noise amplifier (LNA), and an Rx bandpass filter. The effort of bringing these elements together for this market segment in one compact, surface-mount design was quite challenging.

UMTS uses FDD (frequency division duplexing). This means that there is a separate Tx frequency band, 2110 to 2170 MHz, and a separate Rx band, 1920 to 1980 MHz. Therefore, a ceramic duplexer is required at the antenna port so that the picocell can receive and transmit simultaneously. By using a distributed filtering scheme consisting of a duplexer and Tx and Rx bandpass filters, we can provide UMTS attenuation requirements normally seen in much larger solutions. The flexible design allows for a suitable PA and LNA to be added to meet UMTS picocell power and Rx noise figure requirements. In the transmit path, the module can deliver 24 dBm W-CDMA power at the antenna port, while achieving a typical ACLR (adjacent channel leakage power ratio) of -57 dB with a PAR (peak-to-average ratio) of 8 dB. The 3GPP (3rd Generation Partnership Project) specification dictates that a minimum ACLR of -45 dB be achieved under worst case conditions.