A Digitally Intensive Transmitter/PA Using RF-PWM With Carrier Switching in 130 nm CMOS

Abstract

A digitally intensive transmitter using RF pulse-width-modulation (PWM) with a class-D power amplifier (PA) is described. The use of carrier switching for alleviating the dynamic range limitation that can be observed in classical RF-PWM implementations is introduced. The approach employs full carrier frequency for half of the amplitude range and the second harmonic of half of the carrier frequency, for the remainder of the amplitude range. This concept not only allows the transmitter to drive modulated signals with large peak-to-average power ratios (PAPR) but also improves back-off efficiency due to reduced switching losses in the half carrier-frequency mode. A glitch-free phase selector is proposed that removes the deleterious glitches that can occur at the input data transitions. The phase-selector also prevents D flip-flop setup-and-hold time violations. The transmitter has been implemented in a 130-nm CMOS process. The measured peak output power and power-added-efficiency (PAE) are 25.6 dBm and 34%, respectively. While driving 802.11g 20 MHz 64-QAM OFDM signals, the average output power is 18.3 dBm and the PAE is 16% with an EVM of $-25.5\; \text{dB}$ .