This article introduces a 4 x 2 -way Doherty power amplifier (PA) tailored for millimeter-wave (mm-wave) 5G applications. It incorporates an advanced output combiner that consists of four differential 2-way Doherty networks, two quadrature hybrid couplers (QHCs), and a balun to enhance the output power P_out and improves power back-off (PBO) efficiency. Realized in 40 nm CMOS bulk technology with a core area of 1.54 mm², the prototype delivers a saturated power/peak gain surpassing 25.2 dBm/25.5 dB, and it demonstrates a drain efficiency (DE) exceeding 17.5%/10% at 0 dB/6 dB PBO across a 26–32 GHz band. The proposed mm-wave PA achieves error vector magnitude (EVM)/adjacent channel leakage ratio (ACLR) values of −25 dB/−33 dBc for a 2 GHz 64-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing (OFDM) signal with 9.6 dB PAPR, operating at an average output power (P_avg) of 11.3 dBm with an average drain efficiency (DE_avg) of 4% without using digital predistortion (DPD). For a 50 MHz 1024-QAM OFDM signal with 10 dB PAPR, it achieves a P_avg/DE_avg of 7.2 dBm/2% with EVM/ACLR of −35 dB/−42 dBc without DPD.

This article presents a reconfigurable millimeter-wave (mm-wave) fully integrated transceiver (TRX) front end that comprises a power amplifier (PA) and an integrated nonreciprocal ultra-compact isolator/circulator/receiver (RX). The circulator is based on a ring quarter-wave transmission line (QTL) topology with adjusted characteristic impedances, which improves transmitter (TX)-to-antenna insertion loss and TX-to-RX isolation. The circulator’s nonreciprocal gyrator features an and-gate switching-based N-path filter while also acting as a mixer-first RX. By activating the embedded cross-coupled negative resistors, the circulator can be reconfigured as an isolator. This compact N-path filter-based circulator/isolator occupies only 0.38 mm². Over a 27.1–31.1-GHz band, the realized front end offers >20-dB TX-to-RX isolation, with a measured TX-to-antenna insertion loss of 1.7 ⁓ 2.2 dB. The RX path tolerates the PA’s blocker signal, achieving 5-dBm in-band and 13-dBm out-of-band (OOB) B_1dB . The PA delivers 15.15-dBm peak output power with 33% drain efficiency. The functionality of the proposed frequency division duplex (FDD) front end is evaluated by simultaneous TX/RX operation with a 400-MHz TX/RX modulation bandwidth and 400-MHz channel spacing. The measured AM–PM of the realized PA with the integrated isolator shows relatively high voltage standing wave ratio (VSWR) resilience at the lower power level and less robustness against VSWR around its peak output power. The front-end prototype occupies only 0.7 mm², including circulator, PA, quadrature hybrid coupler LO generators, and baseband circuits.

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.

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.

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.

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.

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.

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.

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.