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This article presents a compact 6-bit digital phase shifter (PS) monolithic microwave integrated circuit (MMIC) with low root-mean-square (rms) phase and amplitude errors. A novel bandpass phase-shifting cell (PSC) with embedded high-isolation switches is proposed and adopted in 180°- and 90°-bit designs to compensate the isolation-degradation caused by the large drain-source capacitance of GaN transistors. Then, a systematic design method is investigated to minimize phase and amplitude errors. To validate the proposed techniques, a 6-bit C-band PS is implemented in a0. 25~ m GaN-on-SiC HEMT process with a circuit size of1. 9 2. 5mm2 (0. 03 0. 04 ^2). The measured rms phase error of the proposed PS is less than 1. 2° from 4. 5 to 5. 5 GHz with a 2. 8° calibration bit. The insertion loss (IL) varies between 5. 8 and 8. 2 dB with an rms amplitude error of less than 0. 5 dB. Besides, a good power linearity with 37. 9 dBm input 1 dB compression point (IP ₁\, ₃₁) and 49. 8 dBm input third-order output-referred intercept point (IIP3) is also attained. The proposed PS exhibits superb overall performances in phase resolution, phase/amplitude error control, IL, and power handling capability within a small chip size. It can be a potential candidate for various systems including radars, cellular base stations, and avionic devices.
Zhao et al. (Tue,) studied this question.