An X-band 6-bit High-Accuracy GaAs Digital Attenuator with Low Insertion Phase Shift

This letter presents an X-band 6-bit high-accuracy digital controlled attenuator (DCA) MMIC in a 0.15-μm GaAs process. The insertion phase shift is reduced by introducing an improved attenuation network with shunt compensation capacitors. A simplified T-type attenuation network is used to design 0.5 dB, and 1 dB attenuation cells; Π-type attenuation networks are used for 2 dB, 4 dB, and 8 dB, and switched path structures are used for 16 dB. An inter-stage matching network is introduced between the attenuation units to reduce mutual interference. The attenuation range of the DCA is 31.5 dB with 0.5 dB steps (64 states). The measured results show that the input/output return loss of the DCA is less than -15 dB and the insertion loss is better than -3.9 dB. The root mean square (RMS) amplitude error of the 64-state is less than 0.27 dB and the phase error of the 64-state is better than 2.5°.