A 0.3–4.2-GHz Frequency-Agile Phase Shifter Based on N-Path Passive Mixers Achieving Low Rms Phase/Amplitude Error

This letter proposes a 360° wideband frequency-agile phase shifter utilizing the N-path passive mixer as in- phase/quadrature (I/Q) generator and vector-sum. Implicit capacitor-stacking passive mixers serve as the down-conversion I/Q generator, which provides ~6-dB voltage gain. The passive mixers are driven by four-phase 25% duty-cycle non-overlapping pluses to ensure the I/Q signals with high accuracy. To eliminate the dependence of the amplitude adjustment on high-precision digital-to-analog converters (DACs), the pre-designed trans-conductance ( $G_{m}$ ) cells-based variable gain amplifier (VGA) replaces the conventional Gilbert-based VGA. A prototype phase shifter is fabricated in CMOS 65-nm technology. Measurement results show that the phase shifter has low root-mean-square (rms) gain error and phase error, respectively, less than 0.35 dB and 0.4° over the entire operating frequency range of 0.3–4.2 GHz. The total power consumption is 6–16 mW from a 1.2-V power supply, and the active chip area (excluding pads) is only 0.06 mm ² .