Design of an RF low-noise bandpass filter using active capacitance circuit

• Published in: IEEE transactions on microwave theory and techniques 2005-02, Vol.53 (2), p.687-695
• Main Authors: CHUN, Young-Hoon, LEE, Jae-Ryong, YUN, Sang-Won, RHEE, Jin-Koo
• Format: Article
• Language: English
• Subjects: Active filters; Active inductors; Active noise reduction; Applied sciences; Band pass filters; Bandpass filters; bandpass filters (BPFs); Capacitance; Capacitors; Circuit design; Circuit noise; Circuit properties; Design engineering; Electric, optical and optoelectronic circuits; Electronic circuits; Electronics; Exact sciences and technology; filter noise; Frequency filters; Inductors; Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits; negative resistance circuits; Noise; Noise figure; Performance analysis; Radio frequencies; Radio frequency; Ripples
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2004.840565

In this paper, a novel RF active bandpass filter (BPF) is proposed and its noise performance is optimized by noise analysis. In the proposed design, a resonator consists of an active capacitance circuit together with a conventional inductor. The active capacitor is made of a field-effect transistor that exhibits negative resistance as well as capacitance. It can, therefore, compensate the loss of an inductor. Whereas the conventional active filters using negative resistance circuits usually have a high noise figure, the proposed active filter shows good noise property achieved by adopting a novel active capacitance circuit, which is proven by noise analysis and the experimental result. The measured second-order active BPF shows bandwidth of 95 MHz, 0.1-dB insertion loss, 0.3-dB ripple, and a noise figure of 2.4 dB at the 1.9-GHz band, which agrees well with the simulated results