A Tunable D-Band Filter Based on MOSCAP in 65nm CMOS Technology

In this paper, a D-band varactor-based tunable bandpass filter is proposed in 65nm CMOS Technology. The filter is composed of coupled lines loaded with a pair of MOSCAPs that control the passband of the filter. The effects of MOSCAP parameters in terms of the quality factor and the tuning range are studied. The proper placement of the MOSCAP along the resonator is the key parameter to keep insertion loss as low as possible while the tuning range remains intact. A cross-coupled line between input/output ports introduces a pair of transmission zeros and significantly reduces the size of the filter. The tuning range of the proposed structure is 10 % (136
$\sim $
150 GHz). For this frequency band, the fractional bandwidth (FBW) varies between 10.9 and 11.8 % and the in-band insertion loss is between 4 and 8.2 dB. The overall size of the filter is
$0.11\lambda b _{0} \times 0.095\lambda b _{0}$
. Measurements for the filter show good agreement with the simulation results.