This article presents a wideband series-Doherty power amplifier (SDPA) for millimeter-wave (mm-wave) fifthgeneration (5G) applications. It features a compact two-step impedance inverting-based series-Doherty power combiner that provides broadband close-to-perfect power back-off (PBO) efficiency enhancement. The amplitude-to-amplitude (AM-AM)/amplitude-to-phase (AM-PM) performance of the load-modulated Doherty power amplifier for broadband operation is analyzed. We also devise a post-silicon inter-stage passive validation (PSIV) approach to evaluate the mm-wave chip prototype utilizing the embedded voltage root mean square detectors. The proposed SDPA is realized in a 40-nm bulk CMOS, and it delivers 20.4 dBm P SAT with 39.1%/34% PAE at 0-/6-dB PBO. Over a 23.5-30 GHz band, its PAE is >24% at 6-dB PBO. At 27 GHz, applying a "2 GHz 16-quadratic-amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM)" signal, the proposed SDPA generates 10.2 dBm average power with 18.9% average PAE. The average error vector magnitude is better than −24.5 dB without digital predistortion for a "400-MHz 64-QAM OFDM" signal while generating an average output power of 8.8 dBm with 15% PAE. The AM-AM/AM-PM of the realized SDPA is investigated by employing a "50-MHz 64-QAM OFDM" signal, validating our analysis and showing that the linearity limitation of DPAs is systematic and predictable. Utilizing the proposed PSIV approach, the frequency response of the input/inter-stage passive circuits is measured, indicating an excellent agreement with 3-D electromagnetic (EM) simulation results.
This article presents a wideband energy-efficient transmitter (TX) for 5G mm-wave phased-array systems. It features an advanced double-quadrature direct upconverter (DQ-DUC) to improve its in-band linearity and spectral purity. The proposed TX architecture incorporates an efficiencyenhanced balanced power amplifier (EEBPA) that mitigates VSWR fluctuations in phased-array systems while enhancing efficiency at power back-off (PBO). The EEBPA comprises two identical series-Doherty power amplifiers (PAs) combined through a quadrature hybrid coupler forming a balanced PA. The proposed DQ-DUC consists of a pair of I/Q modulators and the proposed EEBPA's quadrature combiner to further suppress the I/Q image. To verify the proposed techniques, a 40-nm CMOS prototype is implemented. It delivers 20 dBm P 1 dB with 40%/31% drain efficiency at P 1 dB /6-dB PBO. The measured TX output reflection coefficient is better than −18 dB over a 22.5-30-GHz band. Its intrinsic LO feedthrough and imagerejection ratio for a 100-MHz tone spacing over a 24-30-GHz band are better than −45 dBc/50 dB, respectively, without calibration. The average error vector magnitude (EVM) is better than −27.1 dB without digital pre-distortion for an eightcarrier "100-MHz 64-QAM OFDM" signal with an 800-MHz aggregated bandwidth while generating an average output power of 8.4 dBm with 10.8% drain efficiency. Its maximum forwardpower/EVM deviations are better than 0.3/1.65 dB, respectively, for a "100-MHz 64-QAM" signal under a voltage standing wave ratio of 3.
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