A Varactor-Controlled Phase Shifter For PCS Base Station Applications

Introduction

Power amplifiers in today's base stations use compensation techniques to reduce distortion. There are many well-known compensation techniques available, all relying on similar principles of phase and amplitude control. Thus, most (and possibly all) of the compensation techniques use the same control components: voltage-controlled attenuators and voltage-controlled phase shifters.

The quality of these control components strongly determines compensation circuit performance. The ideal phase shifter provides a linear (vs. voltage) 0–360° phase shift with 0 dB change in the signal level; similarly, the ideal attenuator would provide a linear (vs. voltage) attenuation change with 0° phase shift between attenuation settings.

This article describes the design of a high-performance phase shifter for PCS band base station applications. It employs the low-cost SMV1245-011 varactor as the phase-control element and the HY19-12, 90° hybrid. The PCS band was selected because the large number of base stations employed in its infrastructure require an efficient, low-cost solution. However, the methodology employed in this design is applicable to other wireless platforms.

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•Application Note: A Varactor-Controlled Phase Shifter For PCS Base Station Applications