Miniaturised millimetre‐wave BPF with broad stopband suppression in silicon–germanium technology

On‐chip passive distributed‐element‐based bandpass filters (BPFs) usually provide a decent stopband suppression across a limited bandwidth. To solve this drawback without adversely affecting other performance metrics, a simple but effective miniaturised BPF design approach is presented in this work. The proposed integrated BPF topology uses a combination of a coupled‐inductor structure with a pair of metal–insulator–metal capacitors in a quasi‐lumped‐element realisation. To show the operational principles of this BPF approach, a simplified inductor–capacitor‐equivalent circuit model is used for its theoretical analysis. From this analytical framework as an initial design guideline, a quasi‐millimetre‐wave BPF is designed and implemented in a standard 0.13 µm bipolar complementary–metal–oxide semiconductor technology. The measured results show that the developed BPF device has a centre frequency of 28 GHz with a 3 dB fractional bandwidth of 21% and minimum in‐band power‐insertion‐loss level of 3.4 dB. The stopband suppression is higher than 25 dB beyond 45 GHz. The chip size, excluding the pads, is only 0.017 mm 2 (0.06 × 0.284 mm 2 ).