14.3 A Push-Pull mm-Wave power amplifier with <0.8° AM-PM distortion in 40nm CMOS

Millimeter-Wave standards like IEEE 802.15.3c and the new 802.11ad have classifications of their PHY to support single-carrier mode and more complex OFDM mode (high-speed interface) with high peak-to-average ratio (PAPR). To improve the efficiency of power amplifiers (PA), the trend is towards Class-AB and Class-B PAs that exhibit better energy efficiency compared to Class-A. However, Class-AB and -B biasing brings along large amplitude-to-phase-modulation (AM-PM) distortion which degrades EVM and ACPR. At the same time, PMOS transistors become attractive in nanometer CMOS as their f_MAX exceeds 140GHz. This makes it possible to use both NMOS and PMOS transistors at mm-Wave frequencies. This paper presents a 60GHz complementary Push-Pull PA, using both NMOS and PMOS transistors. An inverter-like architecture which uses both PMOS and NMOS results in the cancellation of AM-PM distortion which is particularly important in high-fidelity amplification of OFDM systems and high-order modulation schemes like 16- and 64-QAM, which are very sensitive to phase distortion. Furthermore, the complementary nature allows deep Class-AB operation, giving a high power efficiency at power back-off comparable to state-of-the-art 60GHz PA structures based on NMOS only.