A novel low‐voltage tunable capacitor for tunable RF circuit applications

Abstract

Butterworth Hi-Lo LPF in order to achieve 47.7 to 53 dB attenuation at pole frequency 3.3 -3.0 GHz. Likewise, we need 11-pole classical LPF to achieve 68.7 dB attenuation at 5.1 GHz. The present LPF design provides very compact LPF in terms of order of poles. CONCLUSIONWe reported in this article a 5-pole Butterworth TR-LPF to achieve the attenuation performance of 30-pole classical Hi-Lo LPF. The design is very flexible and a designer can obtain desired compromise between sharpness of cut-off and rejection bandwidth, without changing the order of filter, just by selecting the appropriate pole frequency of a filter. We have obtained 53 dB attenuation for the 5-pole TR-LPF. We have also found in EM-Simulator [9] that the attenuation can be further increased to 72 dB for a 7-pole LPF and 94 dB for an 11-pole LPF. In case of the 11-pole LPF at f c ¼ 2.5 GHz, we can achieve more than 7.1 GHz rejection bandwidth at 70 dB rejection. Such performance is normally obtained with bulky waveguide type LPFs.ABSTRACT: In this article, a novel architecture of the tunable capacitor is proposed for low-voltage applications. In order to reduce operation voltage by enhancing fringing electric fields, two finger-patterned electrodes with zero spacing are vertically separated by employing a multilayer thin-film dielectric of a para-/ferro-/paraelectrics. The proposed tunable capacitor was fabricated on a quartz wafer and its characteristics are analyzed in terms of effective capacitance and tunability with a function of applied voltages, in comparison with the tunable capacitor with the finger-pattern electrode only on the top of the dielectric. At 8 V and 2 GHz, the proposed tunable capacitor shows a tunability of 18% that is 10.3% higher than that of the compared one.