design of a low-noise bpf using active device reduction technique

> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Design of an RF Low-Noise Bandpass Filter Using Active Device Reduction Technique Moon-Seok Chung , Student Member, IEEE, Il-Soo Kim, and Sang-Won Yun, Member, IEEE Fig. 1. The conventional second order active bandpass filter using the acti ve capacitance circuits. Abstract —This letter presents a new design for the RF low-noise bandpass filter (BPF) using the active device reduction technique. In a conventional active BPF based on the negative resistance method, the number of active devices depends on the order of the BPF. In the proposed design the number of active devices is reduced in half, using the suggested new technique. Compared with the conventional active BPF, the proposed one shows better noise figure and consumes less power. We apply this technique to the design of the second order BPF and verify that the measured results exhibit good active filter performances. Index Terms —Active filters, Bandpass filters, Negative resistance circuits. I. INTRODUCTION ONOLITHIC microwave integrated circuit (MMIC)/RF integrated circuit (RFIC) technology is popular because GaAs- and Si-based processes are more common now. Even though there have been many efforts to integrate the whole RF system into a single chip, one of the major difficulties lies in designing of the miniaturized BPFs without sacrificing its typical performances. When we shrink the volume of an integrated RF filter, we usually obtain poorer performances. It is well known that the smaller the resonator size is, the smaller its Q value becomes. Therefore, increasing Q values with a smaller resonator size is the key for the integrated BPF design. In the past several years, many authors have published active filter design methods based on active resonators [1]-[2], active coupling [3]-[4], and other schemes [5]. In those filter configurations, the number of active devices are more than the number of resonators. This letter, on the other hand, presents a new technique that reduces the number of active devices in half. One negative resistance circuit is shared by two resonators in the proposed BPF. Also, an active capacitance circuit employing a BJT and a series-feedback circuit [6] introduces the negative resistance in order to compensate for an insertion loss. The detailed circuit analysis that follows leads us to obtain the equivalent circuit as well as design equations. The proposed active BPF is designed and tested at cellular band (800~900 MHz). We also compare the characteristics of the proposed active BPF with those of the conventional active BPF. Fig. 2. The proposed active bandpass filter u sing active device reduction technique. Manuscript received August 1, 2006; This work was supported by in part by the Agency for Defense Development, Korea, through the Radiowave Detection Research Center at KAIST. The authors are with the Department of Electronic Engineering, Sogang University, Sinsu-Dong, Seoul, Korea (e-mail: [email protected], [email protected]; [email protected]. ac.kr). II. ANALYSIS OF ACTIVE BANDPASS FILTER USING ACTIVE DEVICE REDUCTION TECHNIQUE The conventional active BPF, based on the negative resistance method, is shown in Fig. 1 [7]. The active capacitance circuit, which consists of a BJT and an RLC series-feedback (Rd, Ld, Cd) network, provides the negative resistance to compensate for the parasitic elements of inductors. In the case of the conventional active BPF, the number of active capacitance circuits is as many as the number of resonators. In Fig. 2 we propose a filter network in which an active capacitance circuit is shared by two adjacent resonators, and thereby the number of active devices used can be reduced in half. M

design of a low-noise bpf using active device reduction technique

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