Ultrawideband Distributed Amplifier With Positive Feedback and Intrastack Coupling

This article presents two wideband distributed amplifiers (DAs) to support high data rate communication. The two DAs, respectively, utilize NMOS-only and PMOS/NMOS hybrid gain cells for wideband power amplification in 45-nm CMOS RF silicon-on-insulator (SOI) technology. The gain stages of the proposed NMOS-only DA are capacitively coupled to the input for improving linearity through different biasing modes of each gain stage, while the PMOS/NMOS hybrid DA removes the need for a large on-chip RF choke inductor. Also, the PMOS/NMOS hybrid gain stages can improve amplitude-to-phase modulation (AM-PM) linearity. For both NMOS-only and PMOS/NMOS DAs, intrastack coupling and input-output coupled transmission lines (TLs) are used to support wideband power amplification. Both intrastack coupling and input-output TL coupling are area-efficient. The proposed NMOS-only and PMOS/NMOS hybrid DAs achieve 8.8-/8.0-dB gain, 0.5–137-/ 0.5–67-GHz 3-dB small-signal bandwidth, and 16.5/17.6 peak saturated output power ( $P_{\text {SAT}}$ ) with 15.1%/15.0% peak PAE, respectively. The NMOS-only and PMOS/NMOS DAs support 60-Gbit/s 64-quadrature amplitude modulation (QAM) at 25-GHz carrier frequency with 11.2-/12.4-dBm average output power and 6.5%/5.9% average PAE while maintaining 21.3-/ 21.2-dB SNR [modulation error ratio (MER)]. The PMOS/NMOS DA measures the smallest core chip area among reported CMOS DAs at a similar frequency.

I. Introduction

Over the past few decades, there has been a significant surge in data traffic for both mobile networks and data centers [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], which presents a perennial quest for ultrawide bandwidth, high output power, and high linearity while for a fixed dc power budget [13], [14], [15]. This technology demand has made distributed amplifiers (DAs) an attractive contender due to their ability to support massive bandwidth and superior data rates.