A 60-GHz Variable Gain Phase Shifter Based on Body Floated RF-DAC Structure

In this brief, a 60 GHz variable gain phase shifter based on body floated RF-DAC structure is presented, which is fabricated in 65 nm bulk CMOS process. The proposed variable gain phase shifter consists of I/Q generator and RF-DAC structure based quadrature vector summing amplifier. A low loss and wide band I/Q generator is proposed, which combines a hybrid coupler and a RC poly-phase filter. The vector summing amplifier adapts a pair of RF-DAC structures for each quadrature signal which turn on and off complementarily. This makes the input and output impedances invariant to control states, which are very important characteristics to reduce RMS gain and phase errors of the phase shifter. The RF-DAC cell is implemented with body floated FETs to reduce the Cds at on and off cells for high gain. The RMS gain and phase errors of the proposed phase shifter show 0.13 dB and 0.88°, respectively, at 60 GHz with 3-bits gain control in 8 dB dynamic range, and 5-bits phase control in 360°. In the frequency range of 57 GHz to 62.7 GHz, RMS gain and phase errors show 0.39 dB and 3.01°, respectively. The chip area and overall power consumption are measured to be 0.71 mm2 and 36 mW, respectively.