Synthesis of Capacitive-Coupling-Dominated Topology for Miniaturized Wideband On-Chip Bandpass Filters

In this letter, a synthesis method of capacitive-coupling-dominated topology for a miniaturized on-chip wideband bandpass filter (BPF) is proposed. An inductance normalization synthesis technology is proposed to avoid the excessive use of the inductors in an on-chip filter, since they will introduce extra loss and complex coupling. Utilizing the proposed technique, physical implementable capacitive-coupling-dominated admittance matrix and circuit topology can be synthesized directly. Furthermore, a filter prototype with a minimal number of inductors can be derived with the desired filter order and the location of transmission zeros (TZs). As a result, compact size can be realized without sacrificing insertion loss (IL) due to the reduced number of low-quality-factor ($Q$) on-chip inductors. To demonstrate the proposed method, a four-order BPF with two TZs is synthesized, designed, and fabricated using GaAs integrated passive device (IPD) technology. Good agreement between theoretical results and measurements has been obtained, validating the proposed techniques.