Miniaturized IPD Filter with Flexibly Controllable Transmission Zeros Based on Novel Coupling Theory for 5G Application

In this paper, an on-chip filter is proposed based on two different inductive coupling theories. It is found that flexible response and corresponding miniaturization could be achieved by adjusting the direction of the current flow through the inductor. First, a filtering unit with a customizable transmission zero (TZ) is proposed. It consists of two uncommon double-wound inductors that are symmetrical about the origin. It allows the two inductors to overlap in the horizontal plane so that both inductors have the same direction of signal flows. It reduces the size and excites the horizontal and vertical coupling between the two inductors simultaneously. By adjusting the horizontal distance between the two inductors and the capacitance linked between them, the TZ’s position can be modified flexibly. Then, based on inverting and non-inverting coupling, we implemented a miniaturized on-chip third-order bandpass filter for N77 band. The structure exhibits a flexible response with a large bandwidth and good stopband characteristics with TZs on both sides of the passband. The fabricated prototype filter demonstrates a low insertion loss of 1.63 dB, a 3-dB fractional bandwidth of 43.3%, and an extended upper stopband suppression over 20 dB beyond 27 GHz (> 6.34 f
0
, f
0
= 3.9 GHz). The filter is only 0.85 mm* 0.45 mm in size.