An S/C/X-Band 4-Bit Digital Step Attenuator MMIC with 0.25 mu m GaN HEMT Technology

In this paper, a 4-bit digital step attenuator using 0.25 mu m GaN HEMT technology for wideband radar systems is presented. A switched-path attenuator topology with resistive T-type attenuators and double-pole double-throw (DPDT) switches was used to achieve both low insertion loss and phase/amplitude error. The measured insertion loss of the reference state is 2.8-8.3 dB at DC-12 GHz. The input and output return loss are less than 12 dB at DC-12 GHz. An attenuation coverage of 30 dB with a least significant bit of 2 dB was achieved at DC-12 GHz. A root mean square (RMS) amplitude error of 1 dB and a phase error of 8.5 degrees were achieved, respectively. The attenuator chip size is 2.45 mm x 1.75 mm including pads. To the best of the authors' knowledge, this is the first demonstration of a GaN-based digital step attenuator.