A Cross-Coupled LPF Topology and Design for Millimeter-Wave RFIC Applications

A low-pass filter (LPF) with ultrawide rejection band and compact size by using a cross-coupled topology is proposed. The operating mechanism of the cross-coupled LPF from a unit cell to multiple cells is investigated by using the proposed circuit model. The topology and the circuit model are adopted to design the on-chip LPFs through parameter extracting and electromagnetic optimization. One of the designed cross-coupled LPFs with 1-dB cutoff frequency f
_c
of 2.2 GHz demonstrates the stopband rejection of 30 dB up to 20 f
_c
, i.e., 45 GHz, and the rejection of 20 dB up to 52 f
_c
, i.e., 110 GHz. The measured passband insertion loss is less than 2.2 dB. The size of the LPF is only 350 μm by 280 μm or 0.0089 λg ×0.0071 λg (λg is the guide wavelength on silicon at cutoff frequency).