A 24-GHz single-to-balanced multicoupled line bandpass filter in CMOS technology

In this work, on-chip single-to-balanced bandpass filter centered at 24 GHz is proposed. The functions of bandpass filter and balun are integrated using a simple multicoupled line structure along with capacitive loadings. The use of inductor is avoided such that very compact chip size can be achieved. It can be easily designed with the desired bandpass response and reference impedances through the conventional filter synthesis techniques. Specifically, a 3rd-order single-to-balanced bandpass filter design with a center frequency of 24 GHz and a fractional bandwidth of about 15% is presented using the 0.18-μm CMOS technology. The chip size is 0.533 mm×0.443 mm and the corresponding electrical size is only 0.085λ_g×0.07λ_g at the center frequency. In addition, good selectivity and balanced performance are obtained.