1-chip balanced FBAR filter for wireless handsets

There is great demand for ultra-miniature and balanced RF filters as an essential component in communication systems. To make these needs, we proposed 1-chip balanced FBAR RF filter in this work. A novel FBAR configuration is developed to reduce the area of FBAR block and to enhance performance. And a novel balanced filter topology which can work without trimming inductors is proposed to realize 1-chip balanced RF filter. We also develop the wafer level package using silicon wafers to prevent the increase of size and cost of the filters. The characteristic of fabricated filter is measured 1.75dB as a highest insertion loss in the pass-band (1930-1990MHz) and majority is measured as excellent performance within 1.7dB. Attenuation characteristic is measured very excellent performance as over 33dB in the range between 1850MHz to 1910MHz. In this work, the balanced RF filters are achieved as small as 1.2 mm × 1.2 mm.

I. Introduction

The expansion of the wireless market has given a tremendous push to the development of advanced mobile communication systems [1], [2]. And mobile handsets have been evolved for miniaturization in operating frequencies of the full band. Also, balanced structure has been widely demanded in the low noise amplifier (LNA), for its advantages of common-mode noise rejection, so is the post-LNA filter and balanced duplexer preferred. But almost all the balanced duplexers and post-LNA filters using surface acoustic wave (SAW) are off-chip, even in the latest receiver architectures [3]. These off-chip components become the obstacle of reducing the transceiver size, and they also restrict the noise, gain, and power consumption optimization of LNA, because it is impossible to chose the impedance of off chip filters. For this reason there is great demand for ultra-miniaturization and monolithic integration of the balanced FBAR (Film Bulk Acoustic Resonator) filter and duplexer as a core component in communication systems.