This article introduces an N-way chain-weaver balanced power amplifier (PA) for millimeter-wave (mm-wave) phased-array transmitters (TXs). Taking advantage of the proposed combining network, an embedded impedance/power sensor is implemented, which can be utilized for output power regulation, built-in self-test, and load-based performance optimization. The proposed PA architecture offers linearity and gain robustness under the antenna's frequency/time-dependent voltage standing wave ratio (VSWR). In the event of impedance mismatch, the proposed PA provides N different loads equally distributed on the VSWR circle. Consequently, the performance of the PAs is the average of N PAs with N different loads, which makes this structure VSWR resilient. As a proof of concept, an eight-way chain-weaver balanced PA (BPA) is realized in 40-nm bulk CMOS technology, and it delivers 25.19-dBm P _SAT with 16.19% PAE. The proposed PA supports a 2-GHz 64-QAM OFDM signal with 16-dBm average power, achieving -25-dB error vector magnitude (EVM). The average EVM is better than -30.3 dB without digital pre-distortion (DPD) for an "800-MHz 256-QAM OFDM"signal while generating an average output power of 12.17 dBm. The performance of the PA is also evaluated under 1.5:1-3:1 VSWR conditions. The measured small-signal gain variation under VSWR 3:1 is ±0.7 dB. Moreover, assuming any frequency/time-dependent loading condition within the VSWR 3:1 circle, the proposed chain-weaver BPA achieves <2.8° amplitude-to-phase (AM-PM) over 3-GHz bandwidth. Besides, the embedded impedance/power sensor accuracy outperforms the state of the art. The proposed impedance sensor can measure VSWR 3:1 by the maximum angle and magnitude errors of 12.3° and 0.106, respectively.

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The availability of millimeter-wave (mm-wave) communication systems is a key enabler in developing the fifth generation (5G) mobile networks that offer higher data throughput, lower network latency, and improved link robustness. Namely, they take advantage of mm-wave phased arrays to empower 5G communication systems that establish directional links with large bandwidths between the base station and user equipment. Despite this huge potential, mm-wave 5G has several natural disadvantages. The shorter wavelength of mm-wave signals results in lower penetrability, higher free-space path loss, and susceptibility to atmospheric attenuation, limiting network coverage. Additionally, 5G systems, offering high data throughput, require the use of complex modulation signals and, as such, need to handle large amplitude variations, complicating achieving high energy efficiency. Furthermore, their increased receiver noise lowers the sensitivity and link budget, while their use of Nanometer CMOS technology limits their transmit power and efficiency, impacting system reliability and thermalmanagement.
Unlike digital processors, whose performance and efficiency improve with semiconductor technology scaling, the performance of analog/RF front ends mainly relies on circuit and systemarchitecture innovations. Luckily, operating at mm-wave frequencies unlocks new opportunities, and an approach using those can exceed initial expectations. In this context, this dissertation introduces a series of innovative designs and techniques enhancing the performance and efficiency of power amplifiers (PAs) and transceivers for 5G mm-wave systems....@en

This article introduces a single-supply balun-first three-way parallel Doherty power amplifier (PA) tailored for millimeter-wave (mm-wave) fifth-generation (5G) applications. It incorporates a bandwidth enhancement technique that widens the operational frequency range, enhances broadband power back-off (PBO) efficiency, and reduces impedance mismatch between differential PAs. Realized in 40-nm CMOS bulk technology with a core area of 0.77 mm2 , the prototype delivers a saturated power/peak gain surpassing 20 dBm/16 dB, and it demonstrates a drain efficiency (DE) exceeding 15%/22%/33% at 9.5 dB/6 dB/0 dB PBO across a 24–30 GHz band. The proposed mm-wave PA achieves EVM/ACLR values of − 24.3 dB/ − 30.1 dBc for a 1-GHz 64-QAM OFDM signal, operating at an average output power (Pout) of 9.4 dBm with an average DE of 15%. For a 50-MHz 1024-QAM OFDM signal, it achieves an average Pout/DE of 8.6 dBm/12% with EVM/ACLR of − 30 dB/ − 36.3 dBc.@en

This paper presents a 40nm CMOS mm-wave 3-way Doherty power amplifier (PA) suitable for 5G mm-wave transmitters. It features a bandwidth-enhanced technique using a compact single-supply balun-first 3-way Doherty combiner. The realized front-end with a core area of 0.77 mm2delivers a peak power/gain of more than 20 dBm/16 dB and a drain efficiency (DE) of better than 15 %/22 %/33 % at 9.5 dB/6 dB/0 dB power back-off across a 24-to-30 GHz band. At 26 GHz, it achieves an EVM/ACLR of -23.5 dB/-29.5 dBc for an 800MHz 64-OFDM signal with 9.8 dBm average output power and a 15 % average DE.

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This article presents a wideband series-Doherty power amplifier (SDPA) for millimeter-wave (mm-wave) fifth-generation (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 PSAT 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.

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This work presents an ultra-compact single-antenna FD/FDD transceivers front-end. It comprises a nonreciprocal circulator, RX, and an integrated power amplifier (PA). In the proposed circulator, we devise a ring quarter-wave transmission line topology with adjusted characteristic impedances to improve TX-to-antenna insertion loss and TX-to-RX isolation. Besides, an AND-gate switching-based N-path filter is proposed to realize the circulator's nonreciprocal gyrator while acting as a mixer-first RX. Owing to the ultra-compact N-path filter structure, the circulator occupies only 0.38mm 2 core area. Over a 27.1-to-31.1GHz band, the realized front-end offers >20dB TX-to-RX isolation while its measured TX-to-antenna insertion loss is 1.7~2.2dB. The RX path tolerates the PA's blocker signal, achieving 5dBm in-band and 13dBm out-of-band B 1dB. Moreover, the PA delivers 15.15dBm peak output power with 33% drain efficiency. Our front-end prototype occupies only 0.7mm 2 , including circulator, PA, quadrature hybrid coupler LO generators, and baseband circuits.@en

This letter presents a novel load-modulation-based 3rd-order intermodulation distortion (IMD3) cancellation technique for class-B CMOS power amplifiers (PAs). In a class-B PA, the IMD3 generated by the 3rd-order transconductance ( $g_{m3}$ ) and the gain compression have opposite signs, and thus, they can cancel each other at specific bias and loading conditions. The proposed Doherty topology allows adjusting the gain compression by modulating the effective loading, facilitating IMD3 cancellation over the entire load modulation region. The proposed approach is verified using a 28 GHz 40 nm CMOS series-Doherty PA (DPA) topology. The experimental result demonstrates 10/17 dB IMD3 improvement compared to class-B/DPA operation. Without using any digital pre-distortion, the measured EVM of the proposed technique for a 50 MHz 64-QAM OFDM signal with 8.9 dBm average output power is -38.7 dB (1.2%), which is 5.7/11 dB better than a standard class-B/DPA operation.

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The performance and robustness of millimeter-wave (mm-wave) phased-array transmitters (TXs) define, to a large extent, the quality of a high-data-rate 5G link. In practical situations, however, this TX performance is strongly affected by mutual coupling among the closely-spaced radiating elements in the phased-array antenna, yielding a beam-steering angle-dependent and time-varying loading or VSWR condition. Furthermore, 5G mm-wave systems typically employ spectrally efficient modulation schemes with high peak-to-average power ratios (PAPRs). This requirement demands the TX power amplifier (PA) to operate in power back-off (PBO), thus degrading its average efficiency. To alleviate this issue, outphasing or Doherty PAs (DPAs) can be adopted [1-4]. However, as depicted in Fig. 14.4.1 (Top left), these efficiency-enhancement techniques will worsen the output reflection coefficient of the PA (\Gamma_{{\mathrm {PA}}}). Consequently, the unwanted 'element-to-element' coupled signal reflects back to the antenna and will deteriorate the phased-array beam pattern and its TX linearity. A previously promoted solution for this antenna VSWR problem is load mismatch detection, followed by tuning of the output matching network (self-healing). However, this requires the use of a reconfigurable and inevitably lossy matching network [5]. Also, active load pulling [1] and using a reconfigurable series/parallel DPA configuration [2] have been proposed to realize a VSWR resilient efficiency-enhanced TX. Nevertheless, all these techniques are only suitable when dealing with a known and stable antenna impedance mismatch, which is, unfortunately, not the case in practical situations.

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Continuous Class F (CCF) power amplifiers (PAs) overcome Class-F PA's disadvantage of narrow bandwidth by relaxing the short-circuit requirement at the 2^nd harmonic while still maintaining 90.7% peak efficiency over the band of interest. This paper proposes four different CCF output networks, with their design procedure, suitable for on-chip implementation in the 2.1-2.7GHz band. The output stage with 2^nd harmonic trap and no RF choke is favoured due to its flat real impedance, low fundamental reactance, and compact layout. Using a 40nm CMOS process, a passive efficiency of 68% at 2.4GHz for this structure is in reach.

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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 efficiency-enhanced 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 image-rejection 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 eight-carrier '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 forward-power/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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Line-of-sight millimeter-wave (mm-wave) 5G phased array systems are key solutions to overcome the free-space path loss while providing a multi-Gbit/s data throughput. To realize these systems, nanoscale CMOS technologies should be exploited to enable high integration, compact area, low cost, and high yield. Besides, 5G systems typically employ spectrally efficient complex modulation schemes with high peak-to-average power ratios (PAPRs), which demand the transmitter (TX) power amplifier (PA) to operate in power back-off (PBO), thus degrading its average efficiency. Many techniques such as outphasing [1,2], load-modulated balanced amplifiers (LMBAs) [3–4], and Doherty PAs (DPAs) [5–9] are adopted in mm-wave TXs to enhance efficiency at PBO. Among them, the Doherty is an “RF-in RF-out” PBO efficiency enhancement topology supporting signals with large modulation bandwidth. These mm-wave DPAs are inherently narrowband structures due to employing a lumped-element quarter-wave transmission line (QTL). Thus, the broadband operation is only feasible by increasing the complexity of the Doherty power combiner, compromising with its passive efficiency [7–8]. Also, in these architectures, their optimum PAE at PBO is still narrowband while providing broadband P1dB.@en