A 28-GHz Variable-Gain Phase Shifter With Phase Compensation Using Analog Addition and Subtraction Method

In this letter, a 28-GHz variable-gain phase shifter (VG-PS) with phase compensation designed using a Gilbert-cell-based vector summation amplifier integrated with a current-type digital-to-analog converter (DAC) and a quadrature all-pass filter (QAF) I/Q generator, fabricated using the 90-nm CMOS process. The VG-PS achieves a 360 degrees phase-shifting range with a 7-bit resolution and 7-dB gain-tuning range. The vector summation amplifier synthesizes a vector by combining in-phase and quadrature-phase signals, which are determined by the tail currents of the vector summation amplifier. Tail currents for the vector summation amplifier are generated and mirrored by the current-type DAC. Any mismatch between the DAC's tail current and that of the vector summation amplifier results in amplitude and phase discrepancies in the synthesized vector. The proposed calibration method optimizes amplitude and phase accuracy through current addition and subtraction, eliminating the need for I/Q calibration of the QAF. Measurements show root-mean-square gain and phase errors of the VG-PS at 28 GHz to be 0.12 dB and 0.23 degrees, respectively. The chip size of VG-PS is 0.723 mm(2), including pads, and it consumes 32 mW at maximum gain state.