On-Chip Millimeter-Wave DGS Based Bandstop Filter in 0.18-μm CMOS Process

Defected Ground Structure (DGS) based on-chip bandstop filter (BSF) design is proposed for millimeter-wave applications. In the proposed structure, a capacitively loaded T-shape resonator is embedded in the original DGS resonator, which forms two high quality (<inline-formula> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula>-) factor small loop resonators. Moreover, this structure, in combination with the feedline and series capacitor, independently realizes the position of two transmission poles: one at each side of the parallel resonance without increasing the layout size. The proposed BSF presents a sharp scattering (S-) parameter response due to the appearance of two transmission poles. As a result, the loaded <inline-formula> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula>-factor and negative group delay of the BSF are improved. The prototype of the proposed BSF is fabricated in 0.18-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> Complementary Metal-Oxide-Semiconductor (CMOS) process and measured. The measurement result shows a return loss of 1.78 dB at 53.2 GHz center stopband frequency with the negative group delay of 161 pS. The measurement results also agree well with the electromagnetic simulation results. Without pads, the active area of the prototyped BSF is only 0.024 mm².