A novel bandpass filter using active capacitance

In this paper a novel RF active bandpass filter is proposed. In the proposed design the resonator is made of an active capacitor together with a conventional inductor. The FET-based active capacitor exhibits a negative resistance property as well as capacitive property, and it compensates the resistance from the inductor which consists of the resonant circuit Conventional active filters usually have high noise figure, while in the proposed design good noise characteristics can be achieved. So, the proposed active filter is applicable to the RF front-end design as RFIC or MMIC. The measured 2-stage active bandpass filter shows bandwidth of 52.5 MHz, 0.3 dB insertion loss, 0.3 dB ripple, noise figure of 2.7 dB and OIP3 of 8 dBm at 1.9 GHz, which agrees well with the simulated results.

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