An integrated Q-band 6-bit digital attenuator with low insertion loss

This paper presents a 40–50 GHz low insertion loss 6-bit digital step attenuators. The attenuator has a maximum attenuation range of 31.5 dB with 0.5 dB steps (64 states). It is the first full 6-bit digital attenuator reported over the frequency range of 40–50 GHz to the best of the authors´ knowledge. An accurate field effect transistor´s (FET´s) switch model is developed, which is crucial for the design of attenuator at such high frequency. To reduce the insertion loss, the series transistors of switched T attenuator are removed in the least significant bits (LSBs). The attenuator is fabricated using a 0.15 µm GaAs pHEMT process. The measured insertion loss is 6.5 dB at 40 GHz and 7 dB at 44 GHz respectively. This attenuator exhibits a root-mean-square (RMS) amplitude error of 0.5 dB at 46 GHz, and with the input and output return loss below −10 dB at 40–50 GHz. The core chip size, excluding pads, is 1.8 × 1.05 mm².