Variable duty cycle generation for out-phasing and pwm power amplifiers

Abstract

Power reduction in transmitters is very important. One method to realize reduction is to make use of switching power amplifiers (PA) that have a better efficiency. Switching PA concepts are only possible in combination with suitable modulation methods like pulse width modulation (PWM) and out-phasing concepts. However, PWM and out-phasing concepts rely on accurate phase control and duty cycle of the signals. Digitally generation of signals of variable duty cycles and phase is proposed without sacrificing their accuracy. Accordingly, a out-phasing power amplifier arrangement is disclosed, where the generation of the out-phasing angle (θ) and duty cycles (dand d) are controlled by a set of n-bit digital input words (D, D, D, D). The baseband phase information (φ(t)) is phase modulated back to radio frequency and used as the clock signal of digital circuitry for phase and duty cycle generation after being frequency multiplied by 2. The resolution of the out-phasing angle and of the duty cycle is 2π/2and 2π/2equivalently. The resolution of the phase information φ is dependent on the PM realization.