PWM Controlled 180 degrees Analog Phase Shifter

Phase shifter is an important building block in radio frequency (RF) beamforming and multiple-input multiple-output (MIMO) systems to control the phase of the signals transmitted from the multiple antennas. This paper presents a switched-capacitor based analog phase shifter using a lattice phase equalizer, where the phase change occurs from 0 degrees to -180 degrees and the magnitude remains constant. The input signal's phase is adjusted by changing the equivalent shunt capacitances of the lattice phase equalizer by synchronously switching between two capacitors connected at the input and output sides. A pulse width modulated (PWM) signal is applied to the controlled switches connected in series with each capacitor. Thus, the phase difference is a function of the duty cycle of the PWM signal. The proposed concept is theoretically proved, the design is simulated using 65 nm CMOS technology at different frequencies, and implemented in hardware for design validation. The root mean squared error (RMSE) between the simulated and measured phase difference is 0.7 degrees, which is much lower than the error achieved using the other competitive methods.