A compact and tunable active inductor-based bandpass filter with high quality factor for Wireless LAN applications

A fully-differential compact and tunable second-order bandpass filter (BPF) with high quality factor using a novel active inductor (AI) has been proposed for 3.6 GHz WLAN applications. The proposed AI employs a differential amplifier as a feedforward transconductor and a common-source (CS) transistor as a feedback transconductor in a symmetrical configuration. The combination of a cascode scheme and a resistor in the feedback path enhances the quality factor of the AI, thereby increasing the mid-band gain of the BPF. In order to achieve independent tuning of both the center frequency and mid-band gain of the BPF, a varactor capacitor is utilized. The proposed second-order BPF is designed with a center frequency and a bandwidth of 3.675 GHz and 10 MHz, respectively. Post-layout simulation, process corner, and temperature sweep analysis results are conducted with 65 nm CMOS technology at 1.2 V supply voltage. The proposed filter has a tuning range of 3.655–3.695 GHz and attains a mid-band gain of 67.5 dB, a noise figure of 14.5 dB, and a 1-db compression point of −12.39 dBm. Additionally, the BPF consumes a DC power of 1.22 mW and occupies an active area of only 8.85 $\mu$m $\times$ 10.3 $\mu$m.