A Si-CMOS 5-bit baseband phase shifter using fixed gain amplifier matrix

For millimeter wave beam forming system, instead of using phase shifter at very high frequency of radio frequency (RF) or local oscillator (LO) frequency, low frequency baseband (BB) phase shifter has more potential for realization. Conventional BB phase shifters use variable gain amplifiers (VGA), which have low linearity, and calibration is required for over 3-bit BB phase shifters. In this paper, we propose a novel BB phase shifter using fixed gain amplifiers (FGA) matrix with in/out-phase switches. Since FGA normally has higher linearity than VGA, it is possible to reduce overall power consumption to achieve same linearity. FGA has fixed reflection and transfer characteristic, so mismatch between phase shift states are reduced. By dividing phase shifter into smaller stages, the effects of process mismatches on very nearby transistors are small. So proposed structure has robustness against process mismatch. Fabricated 5-bit BB phase shifter using proposed method has a very low power consumption to achieve almost same linearity as other works and has a 3-dB bandwidth of 1.2 GHz, 1.5° of rms phase error, lower than 0.2 dB of rms gain error without calibration. For ambient temperature from -20°C to 80°C, simulated rms phase error varied by only 0.2°, and did not vary with process mismatch.