An On‐Chip Elliptic Bandpass Filter With High Selectivity and High Stopband Attenuation Near the Passband Based on Stacked Series‐Parallel Topology

ABSTRACT In this paper, a high selectivity integrated passive device (IPD) on‐chip bandpass filter is presented. The passband can be constructed by using a minimum number of three‐order elliptic bandpass filter. The stacked series‐parallel topology is employed to generate two transmission zeros (TZs) and a transmission pole (TP) to maintain high selectivity and high stopband attenuation near the passband. Moreover, in order to deep the attenuation level at the upper stopband, a zero‐pole generation circuit is introduced at the input and output ports to generate a TZ and a TP, which can also adjust the flatness of the passband and improve the impedance matching. An IPD on‐chip filter sample is fabricated with an electric length of 0.12 × 0.05 λg 2 . The measurement results show that the centre frequency is 4.2 GHz, the fractional bandwidth is 78.6%, the minimum in‐band insertion loss is 1.23 dB, and the frequency selectivity SF 20dB and SF 30dB are 1.31 and 1.39, respectively.