Large-Swing 22nm Si/SiGe FDSOI Stacked Cascodes for 56GBaud Drivers and 5G PAs

Abstract

High bandwidth and high datarate large-swing optical-modulator-driver and 5G-PA output stages are reported. These series-stacked n-MOS and CMOS cascodes employ a new varactor-based scheme for output resistance and output swing tuning, without affecting the imaginary part of the output impedance and without placing matching networks on the signal path. Record 18Gb/s 64-QAM constellations with EVM lower than −30 dB at 10 dBm output power were measured at 5.5 GHz and 28 GHz, as well as 112 Gb/s (4-PAM) operation with $2.4\mathbf{V}_{\mathbf{pp}}$ output swing when the cascodes are used as linear broadband optical modulator drivers. The saturated output power, $\pmb{P}_{\mathbf{SAT}}$, of a single-ended stacked CMOS stage remains larger than 17 dBm from 1 to 45 GHz, with a peak of 19 dBm and PAE of 53.8% at 5.5 GHz, without any input and output matching network. A 4x MIMO transmitter with a differential version of the stacked CMOS output stage would meet the targeted 5G $\pmb{P}_{\mathbf{SAT}}$ of 28 dBm from 0.5 to 28 GHz. These results suggest that a single CMOS transceiver and PA could cover all the 5G bands from 0.5 GHz to 45 GHz. The n-MOSFET cascodes show better PAE above 10 GHz (33.4% at 28 GHz) than the CMOS version but with 1–2 dB lower $\pmb{P}_{\text{SAT}}$ and linearity.