Phase-locked loop based PWM wireless transmitter

A Cartesian transmitter based on pulse width modulation, with the capability to drive a switched power amplifier, such as a Class D stage, is presented. A phase-locked loop based technique is proposed to generate a high frequency pulse width modulated signal with a 1.28 GHz carrier. This signal is subsequently upconverted and applied to the output stage. This technique does not require a ramp generator or a high-precision voltage comparator, that are typically employed in conventional pulse width modulators. A prototype is simulated in a 130 nm CMOS process, and achieves 35% peak efficiency for 17 dBm output power with a center frequency of 900 MHz. Operation of the architecture with modulation that has a non-constant envelope is verified in simulation.