A Miniaturized On-Chip Bandpass Filter With Ultra-Wide Stopband for RF SoC Applications

In this brief, a novel design method for on-chip bandpass filter (BPF) is proposed, analyzed and validated. By inserting a highpass filter (HPF) into the lowpass filter (LPF), a BPF with wide stopband can be realized without increasing the die size. The introduction of source-load coupling technique and series inductor in a pi-type LPF can generate three transmission zeros (TZs), which extends the upper stopband considerably. To improve the selectivity, the source-loading coupling technique is also used in the HPF design. Moreover, a stacked MIM capacitor working at its self-resonant frequency is used to replace the series LC resonator in the BPF to further reduce the size and decrease its sensitivity to process deviation. An amplifier is also designed to validate integration. Finally, a prototype was fabricated in a 2-mu m GaAs HBT process to verify our methodology. The filtering amplifier achieves a 3-dB fractional bandwidth of 78.9% (2.3-5.3GHz). The upper stopband with rejection level of 34 dB reaches to 68GHz (> 17.8f0). To the best of our knowledge, this is almost the widest harmonic rejection achieved with such a small size (600 x 500 mu m2). The designed BPF could be well used in a high-density integrated system on chip like satellite and 5G communication, etc.