High-Resolution Wideband Vector-Sum Digital Phase Shifter With On-Chip Phase Linearity Enhancement Technology

In this paper, a wideband vector-sum phase shifter with phase linearity enhancement technology is proposed to minimize phase error. The digital phase shifter synthesizes the output phases by modulating and summing four quadrature signals. A common-source stage with transformer-based matching network and a quadrature-all-pass filter (QAF) are utilized for the quadrature signals generation within a wideband. Besides, to decrease the influence of parasitics on amplitude and phase error, a resistor-based compensation technology is employed in the QAF implementation. Then, to obtain the 360° range high resolution phase shifts, the quadrature signals are modulated by four Gilbert-type variable gain amplifiers (VGAs) with digital-controlled current-digital to analog converters (current-DACs). To further minimize phase error, an on-chip phase linearity enhancement loop is utilized. The drain voltages of current-DACs are detected and compared to the presupposed reference voltages generated by the loop. Besides, the compared results are fed back to control the current-DACs to achieve phase linearity enhancement. To verify the mentioned mechanism, a 7-bit digital phase shifter operating at 22-44 GHz with on-chip phase linearity enhancement technology is implemented and fabricated in a 28-nm CMOS technology. Based on the phase linearity enhancement technology, the phase shifter exhibits a RMS amplitude error of 0.36-0.59 dB and RMS phase error of 0.92° -1.02° without off-chip digital pre-distortion (DPD) technology. The total DC power consumption including the phase linearity enhancement loops is 35 mW under a 0.9V supply voltage.