A 6–18 GHz Active Variable Attenuator With Minimized Phase Variation

This paper presents a 6–18 GHz 7-bit digitally controlled active variable attenuator with phase-invariant technique in 40-nm CMOS technology for wideband active phased-array applications. A current-steering structure is implemented in the attenuator for attenuation tuning while the phase-invariant technique is proposed to reduce phase variation between different attenuation modes. In addition, the inductive peaking technology is utilized for bandwidth extension and gain flatness. The proposed active attenuator exhibits a simulated attenuation tuning range of 15.5 dB with 0.5 dB steps, while the Root-Mean-Square (RMS) amplitude error and phase error within 6–18 GHz are better than 0.2 dB and 2.5°, respectively. The gain variation at each attenuation mode is less than 1.2 dB and the input 1 dB compression point (IP1dB) @ minimum attenuation mode is higher than -1.8 dBm at 1.2 V supply.