<title>Design considerations for high pass frequency passive filters</title>

Abstract

Two high pass filters at 2.4 GHz and 5.2 GHz frequencies in SiGe 0.8μm process are presented. Design process and measurement results are discussed. This paper evaluates electromagnetic coupling, and presents a theoretical filter model which takes into account these effects, it also enumerates some design considerations to improve passive components design. A previous model of passive components is ilustrated, and the main conclusions are exposed to justify inductor and varactor election. Some inductors and varactors were manufactured previously to study how to improve the quality factor and to ensure accurate inductance and capacitance values. Different geometries for these passive components were designed, fabricated and measured, the best inductor and varactor election for filter design is based on these measurement results. After components election is carried out, the filter architecture is explained. The election of the optimal filter configuration is based, among other considerations, on minimizing passive component number, especially inductors. By achieving the lowest quality factor for inductors, filter characteristics improve by diminishing inductor number, therefore, the selected filter order is three, and just one inductor is used. Once the filter designs are manufactured and measured some non-modelled effects are appreciated and studied from the measurement results. These effects produce a pass band attenuation degradation, cut-off frequency deviation and resonant behavior at frequencies below cut-off frequency. To check what these effects are due to, electromagnetic coupling effect simulations are made using CADENCE simulator. This electromagnetic analysis helps evaluate the interaction effects between passive components. Electromagnetic simulations agree with the filter degradation measurement results.