On-chip tunable low pass filter with improved stopband using new cross coupled topology

A new type of low pass filter with ultra-wide rejection band and compact size by using a cross coupled topology (CCT) is proposed. The topology and circuit model are adopted to design the on-chip low pass filters through parameter extracting and electromagnetic optimization. One of the designed CCT low pass filters with 1-dB cutoff frequency f_c of 2.2 GHz demonstrates the stopband rejection of 30dB up to 20 fc i.e. 45 GHz and rejection of 20dB up to 52 f_c i.e. 110GHz. The measured passband insertion loss is less than 2.2 dB. The size of the low pass filter is only 350 μm by 280 μm or 0.0089 λg × 0.0071λg (λg is the guide wavelength on silicon at cutoff frequency). With the size chip area, a tunable CCT LPF is introduced to further improve the stopband rejection and rolloff.