A 28–40-GHz Digital Step Attenuator With Low Amplitude and Phase Variations

This letter presents a 28–40-GHz 5-bit digital step attenuator (DSA) in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. The DSA achieves low amplitude and phase variations by using the following techniques: 1) combination of distributed, T-type, and modified $\Pi $ -type attenuators can ensure a low amplitude variation while maintaining a compact size; 2) interstage matching is designed to relax the loading effect between each stage; 3) inductive compensation is adopted to reduce the phase error for 8- and 16-dB attenuation cells. The DSA exhibits a 31-dB tuning range with 1-dB tuning step. The measured rms amplitude and phase errors are < 0.43 dB and < 5.4° over 28–40 GHz, respectively. The insertion loss is 5.4–9.1 dB from 28 to 40 GHz.