A 120-GHz Bandwidth CMOS Distributed Power Amplifier With Multi-Drive Intra-Stack Coupling

• Published in: IEEE microwave and wireless components letters Vol. 30; no. 8; pp. 782 - 785
• Main Authors: El-Aassar, Omar, Rebeiz, Gabriel M.
• Format: Journal Article
• Language: English
• Published: IEEE 01.08.2020
• Subjects: Bandwidth; CMOS silicon-on-insulator (SOI); Couplings; Frequency measurement; Gain; gainbandwidth product (GBW); Impedance; instrumentation; Logic gates; Mach-Zehnder Modulator (MZM) driver; millimeter-waves; optical-wireline; power amplifier (PA); Power measurement; stacked amplifier; transformer; ultrawideband (UWB)
• ISSN: 1531-1309; 1558-1764
• DOI: 10.1109/LMWC.2020.3001261

This letter presents a distributed power amplifier (DPA) topology that improves both the power combining efficiency and the operation bandwidth. Multi-drive intra-stack coupling is introduced in the design of the gain cells to break the tradeoff between high output power (<inline-formula> <tex-math notation="LaTeX">P_{\text {OUT}} </tex-math></inline-formula>) requirement and the achieved bandwidth. The proposed technique also compensates for the input transmission line (TL) loss to accommodate more stages and achieve flat gain and higher <inline-formula> <tex-math notation="LaTeX">P_{\text {OUT}} </tex-math></inline-formula>. A prototype eight-stage, 16-dB gain, 120-GHz bandwidth DPA is fabricated in 45-nm CMOS silicon-on-insulator (SOI) using elevated coplanar waveguide (CPW) TLs with a core area of 0.51 mm 2 . The amplifier maintains an output <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {1\,dB}} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {SAT}} </tex-math></inline-formula> higher than 18 and 20 dBm, respectively, up to 60 GHz and achieves a peak PAE of 19.7% at 15 GHz. A 64-quadrature-amplitude modulation (QAM) modulated signal with data rate 30 Gb/s (5 GBaud/s) is demonstrated at 55 GHz with a 13.5 dBm average <inline-formula> <tex-math notation="LaTeX">P_{\mathrm {OUT}} </tex-math></inline-formula> and 6.9% PAE while the error vector magnitude (EVM) is kept below 5%. To the authors' knowledge, the achieved 757-GHz gain-bandwidth product (GBW) is the highest among reported non-cascaded DPAs. The DPA has also the highest continuous-wave (CW) and modulated PAE compared to other reported distributed amplifiers (Das).