Design and Analysis of a Differential, Wideband Digital Step Attenuator

A wideband digital step attenuator with a differential structure based on 0.15-μm GaAs pHEMT process is designed. The parasitics of metal bonding lines are avoided by importing virtual ground using differential structure. By applying simplified T-type, T-type and Π-type attenuation extensions, appropriate selection of transistor size and resistance, and the use of capacitance compensation structures, high attenuation accuracy from DC to 25 GHz is achieved. The designed digital attenuator exhibits ultra-wideband operation with 15.0-dB amplitude tuning range and 1-dB tuning step. In the 25 GHz bandwidth, the reference state insertion loss is 3.1- 4.9 dB, and the root-mean-square (RMS) attenuation error is less than 0.3 dB, RMS phase error is less than 8.0°.