Common‐mode suppression for balanced bandpass filters in multilayer liquid crystal polymer technology

Abstract

A new multilayer differential transmission line for common-mode suppression fabricated using an organic liquid crystal polymer multilayer substrate is proposed and analysed. The structure consists of a pair of parallel strip lines printed on the top layer of the substrate that are capacitively coupled to conductor patches periodically etched in an intermediate interface. These patches are symmetrically connected to a solid ground plane by means of short-circuited high-impedance microstrip line sections and metalised via holes. The differential signal supported by the coupled strips is not significantly affected by the presence of the middle layer layout, whereas the common-mode signal propagation is strongly suppressed within a certain frequency band. When this structure is cascaded with a simple differential bandpass filter exhibiting poor common mode rejection, a good common mode response is achieved within the unperturbed differential passband. The measurements confirm a significant enhancement of common-mode rejection thanks to the use of the proposed differential lines.

Transversely Compact Single-Ended and Balanced Bandpass Filters with Source–Load-Coupled Spurlines

“…As compared with the works reported in [11,13] and [15], the proposed one has similar insertion loss and the largest number of TZs, which means the proposed one exhibits better Table 1 summarizes the comparison between the proposed balanced filter and some similar reported works. As compared with the works reported in [11,13,15], the proposed one has similar insertion loss and the largest number of TZs, which means the proposed one exhibits better selectivity performance. Moreover, the proposed balanced filter has wider a stopband, with about 20 dB out-of-band rejection as well.…”

“…However, it needs to undergo micromachining fabrication and wire-bonding processes, which are complex [9]. A dual-band balanced filter based on open-ended half-wavelength UIR resonator and interdigital capacitor is proposed in [10], while another case was made of a short-ended half-wavelength UIR resonator with multilayer structure [11]. In [12], the aggressive space mapping method is utilized to synthesize a balanced filter incorporating the SIR, which achieves an excellent common mode rejection ratio (CMRR) about 50 dB.…”

Miniaturized Common-Mode Filter Using Coupled Synthesized Lines and Mushroom Resonators for High-Speed Differential Signals

“…Comparable eye widths and heights are observed, indicating almost identical signal integrity for both cases. Table I compares the proposed miniaturized CM filter with the state-of-the-art designs using standard PCB [1], [2], [4], [5] and LTCC processes [3]. The CM rejection bandwidths are estimated from the literature with dB.…”

“…Similar to [1], two meander-line inductors are connected at the edges of the capacitive patch, in order to make the resonance frequency of the tank coincide with the targeted CM rejection band. Unlike those in [1], [2], without a patterned ground plane, the parasitic radiation and unwanted EM interference can be alleviated, and the power integrity can be retained.…”

Common-Mode Suppression Design for Gigahertz Differential Signals Based on C-Slotline

“…The common-mode suppression behavior is also investigated based on planar electromagnetic bandgap structures by Orlandi et al in [8]. Besides, the artificial transmission line [9] and the multilayer liquid crystal polymer technology [10] are used in the common-mode suppression as well, and the balanced bandpass filters based on them are successfully designed.…”