Inductor-less SiGe pin diode attenuator with low phase variations

An inductor-less wideband (6-18 GHz) 3-bit attenuator with low phase variations is presented based on octagonal SiGe p-type intrinsic n-type ( pin) diodes. To achieve low insertion loss and high linearity, a DC bias scheme has been designed to minimise the leakage from the parasitic diodes between the P-sub and N-well of the pin diodes. The attenuator is fabricated in a standard 0.18 mm SiGe BiCMOS process without using post-processed transmission lines. It has a maximum attenuation range of 7 dB. The minimum measured insertion loss is 7.9, 9.4, 10.6 dB at 6, 12, 18 GHz, respectively. Phase variation is lower than ± 2.5° and the chip size, including pads, is 0.85 x 0.412 mm².