Efficiency enhancement of CMOS transmitters using class-G supply modulation and pulse-width modulation

Techniques to improve the efficiency of modern digitally modulated transmitters are introduced in this work. Digitally modulated transmitters introduce both phase and envelope variation in order to improve spectral efficiency; envelope variation results in lower efficiency performance for traditional transmitter architectures.;A pulse-width and pulse-position modulation (PWPM) transmitter is proposed to efficiently transmit signals with envelopes having small peak-to-average ratios (3-6 dB). The PWPM transmitter is combined with a class-E power amplifier (PA) to exploit the ever improving switching performance of scaled CMOS. The transmitter exploits the fact that a class-E PA is insensitive to amplitude variation at its input, but is sensitive to pulse-width variation. Envelope information is encoded in the duty cycle of the PA input signal. The class-E PA has much larger peak efficiency than traditional linear PAs and the efficiency characteristic versus pulse-width, and thus envelope, is always greater than the efficiency characteristic of a linear PA versus input envelope.;A second technique is proposed for systems with larger peak-to-average ratios (6-15 dB). This technique uses direct power supply modulation of the class-E PA in order to restore the signal envelope. A class-E PA is sensitive to variations in the voltage being supplied to the PA. The system's efficiency is dominated by the supply voltage from which it operates. In order to improve the efficiency, a circuit is developed which allows for operation from a more optimal supply voltage in order to improve the efficiency of the system.;Prototype circuits are fabricated to demonstrate the functionality of the circuit. A PWPM transmitter and PA is fabricated in 65 nm CMOS and achieves excellent output power and efficiency, 28 dBm and 29%, respectively. A class-G dual-supply modulated transmitter and class-E PA is fabricated in 130 nm CMOS. This PA achieves 29 dBm and 69% efficiency.