A CMOS digital step X-type attenuator with low process variations

In this paper, a digital step X-type attenuator with low process variations is demonstrated using 90 nm CMOS technology. The X-type attenuator uses MOSFETs as voltage controlled resistors, which influenced by process parameters. And a compensation circuit associated with the threshold voltage is employed to mitigate the process influence. The attenuator have a maximum attenuation range of 32 dB with 0.5 dB steps. The rms amplitude error and rms phase error are 0.42 dB and 3.1° over 23.5–30 GHz respectively, and the insertion losse is 9.77 dB at 25 GHz. The core chip size is 0.48mm².