Packaged Cmos Transmission Line Based Active Bandpass Filter with High Stopband Suppression

This paper presents a packaged third-order transmission line based (TL-based) active bandpass filter (BPF), which is fabricated using Silterra's standard 0.18-μm CMOS 1P6M technology, with high stopband suppression. The active compensating circuit, which produces differential negative conductance, improves the quality factor (Q factor) of TL-based resonator and suppresses the spurious resonances at even-harmonic frequencies. The spurious responses are also shifted towards higher frequencies by applying a capacitively loaded TL resonator method to the filter design. Additionally, an inductive parasitic effect introduced by the package is investigated and reduced to achieve the minimum impact on the stopband suppression. Measurement results indicate that the prototype has an insertion loss of 0.95 dB at a central frequency (f) of 1.53 GHz with a 3-dB bandwidth of 3.1%, while a current of 8 mA is consumed from 3.0 V. The stopband suppressions at 2f and 3f are 44.57 dB and 52.78 dB, respectively. Furthermore, the suppression exceeds 35 dB from 1.08f to 10.05f.