Research And Design Of 28 GHz Variable Gain Bidirectional Active Phase Shifters

Millimeter-wave frequencies and phased-array techniques are usually utilized to expand channel bandwidths and improve the efficiency of spectrum resources through spatial multiplexing,boosting the available wireless data rate significantly.The phase shifter,one of the most important modules of the phased array system,provides the necessary phase shifting for beamforming of array antennas,and radio-frequency phase-shifting architectures can reduce areas and costs by sharing one phase shifter in the TX mode and the RX mode.Millimeter-wave integrated circuits are traditionally based on III-V semiconductor processes,but the development of CMOS processes has reduced the costs and power consumptions of millimeter-wave integrated circuits,making beamformer chips with multi-channels possible.Therefore,the phase shifters in the phased array system are studied in this thesis,and 28 GHz silicon-based variable gain bidirectional active phase shifters are designed.These two phase shifters have the advantages of low errors,a compact area,variable gains and the bidirectional operation which is realized by switches.They based on the vector-summing phase shifter are both divided into four parts,including a second-order polyphase filter,a vector modulator,a digital control circuit and impedance matching networks.Orthogonal signals with low errors and low amplitude errors are generated by the Type-Ⅱ second-order polyphase filter based on passive RC networks.Adjusted by the digital control circuit,a Gilbert unit as the front stage of the vector modulator is adopted to realize 360° phase shifting by the amplitude modulation of the quadrature signals and a variable gain amplifier with low phase variations is utilized to modulate gains as the latter one.The 5bit signal for the phase modulation and the 4bit signal for the gain modulation input from the outside are converted into control signals by the decoding circuit in the digital control circuit for the current array to adjust the vector modulator.The post-simulation results of the phase shifter designed without transformers or Baluns show that the RMS phase errors of TX and RX modes are less than-3.4° and-4.2°,the RMS gain errors are both less than 0.54 d B during the phase adjustment,and the RMS phase errors during the gain adjustment of 11.25 d B are less than 1.9 and 1.0° in TX and RX modes,from 26.5 to 29.5GHz.In order to reduce the phase errors and gain errors,and improve the anti-electromagnetic interference,the impedance matching between amplifiers and the conversion between the differentialend and the single-ended are realized by transformers and Baluns designed in this thesis.The broadband matching based on transformers is used between the Gilbert unit and the next stage to decrease the error away from the center frequency during the phase modulation.The post-simulation results of the phase shifter designed with transformers and Baluns show that the RMS phase errors of TX and RX modes are less than-3.0° and-2.4°,the RMS gain errors are less than 0.65 d B and 0.30 d B during the phase adjustment,and the RMS phase errors during the gain adjustment of 11.25 d B are less than 2.5° and 1.2° in TX and RX modes,from 26.5 to 29.5GHz.