A New Wideband, Low Insertion Loss SiGe Digital Step Attenuator A New Wideband, Low Insertion Loss SiGe Digital Step Attenuator

Abstract

This paper presents a new, wideband digital step attenuator (DSA) implemented using SiGe HBTs. The vertical profile of the SiGe HBT presents small parasitic shunt capacitance and, thus, the loss from the switches in a switched-type attenuator is significantly reduced. For a 6-bit DSA covering a maximum attenuation of 31.5 dB with 0.5 dB steps, reduced T-type cells with reverse-saturated SiGe HBTs are used for low attenuation cells and switched pi-type cells with novel anti-parallel (AP) SiGe HBT pair series switches are used for high attenuation cells. In addition to the symmetry of the AP SiGe HBT pair, reduced T-type and switched pi-type cells are placed alternately to distribute parasitic components and to achieve better overall symmetry. As a result, state-of-the-art performance is achieved over a wide bandwidth, from DC-to-60 GHz, with an insertion loss of 7.5 dB at 50 GHz, 31.5 dB of attenuation range and less than 2.8 mW of power consumption.