Very Compact Full Differential Bandpass Filter With Transformer Integrated Using Integrated Passive Device Technology

Abstract—In this study, a very compact, second-order, full differential bandpass filter is presented. To achieve compact circuit area and system-in-package (SiP) applications, the transformer structure is integrated using integrated passive device (IPD) technology on a glass substrate. The coupled resonator synthesis method is used to achieve the bandpass filter design and suitably adjust the tapped feed-lines to obtain good impedance match at all ports. The area (1.27mm×1.27mm) of the bandpass filter is effectively reduced, and the performance, as measured by insertion loss (2.5 dB) and CMRR (> 30 dB), is still acceptable with such a compact area. Most importantly, this full differential bandpass filter is also suitable for SiP applications, as other studies implemented using glass IPD technology have demonstrated. 1.