Search Results (9)

A high-power and high-repetition KTiOAsO₄ (KTA) optical parametric oscillator (OPO) was established in this study, with the adoption of plane-parallel and ring cavities. The pump was a high-power Nd:YAG master oscillator power amplifier (MOPA) system with a pulse repetition frequency (PRF) of 300 Hz, and the corresponding beam quality factors were M_x² = 3.4 and M_y² = 3.2. In the plane-parallel cavity experiment, powers of 51.1 W (170 mJ) and 15.9 W (53 mJ) in the signal and idler were obtained, respectively. In terms of the average power of 1 μm of a pumped KTA OPO, to our knowledge, this is the highest average power for KTA OPO. The ring cavity was constructed to achieve lasers with both high power and beam quality. The output powers of the ring cavities for the signal and idler were 33.9 W (113 mJ) and 8.7 W (29 mJ), respectively, and the corresponding beam quality factors of the signal were M_x² = 5.3 and M_y² = 7.9. The 300 Hz 100 mJ class 1.54 μm laser with a beam quality factor of less than 10 is an ideal eye-safe light detection and ranging (LiDAR) source. Full article

This paper presents an X-band high-power GaN MMIC power amplifier (PA). To balance efficiency, output power, and saturated power flatness, the load-line theory is employed to analyze and validate the power variation trends within an extended continuous Class B/J (CCBJ) impedance space. Theoretical constant power contours are plotted within this space. An L-C impedance matching network is used to match the amplifier’s output impedance to the overlapping region of the 0.5 dB constant power contour and the CCBJ impedance space, significantly improving the in-band power flatness of the PA based on the CCBJ design approach. Additionally, an RC parallel structure is integrated into the interstage matching network to maximize gain while ensuring stability. The proposed PA, implemented using a 0.25 µm commercial GaN process, achieves a saturated output power of 47–47.6 dBm with in-band fluctuations within ± 0.3 dB, a power gain of 27.0–27.8 dB, and an efficiency of 40–45.5% across the X-band. Full article

This paper presents two power amplifiers designed for 5G NR n77 and n78 bands. These power amplifiers were fabricated using WIN^TM Semiconductors’ 0.25 μm GaN/SiC technology and GaAs IPD technology. To achieve a reduction in costs, GaAs IPD technology was incorporated in the design, leading to the realization of a quasi-monolithic microwave integrated circuit design. To ensure high power, high efficiency, and broadband operation, a continuous Class-J mode output matching network was utilized. The power amplifier with split chip-on-board wire-bond assembly had a power gain of 21.7 dB, a 3 dB power bandwidth ranging from 2.85 GHz to 4.48 GHz, a saturation power of 40.3 dBm, and a peak power-added efficiency of 39.5%. On the other hand, the power amplifier with stack chip-on-board wire-bond assembly had a power gain of 21.7 dB, a 3 dB power bandwidth ranging from 2.84 GHz to 4.47 GHz, a saturation power of 40 dBm, and a peak power-added efficiency of 36.5%. For a 5G NR FR1 256-QAM 100-MHz bandwidth modulated signal with a frequency range of 3.3 GHz to 4.2 GHz, both the split and stack chip-on-board wire-bond assembly power amplifiers achieved average output powers of 29.6 dBm and 28.3 dBm, respectively. These output powers were measured under an error vector magnitude requirement of 3.5%. Full article

High-power solid-state lasers are among the hot research directions at the forefront of laser research and have major applications in industrial processing, laser-confined nuclear fusion, and high-energy particle sources. In this paper, the properties of Yb:YAG and Nd:YAG crystals as gain media for high-power solid-state lasers were briefly compared, according to the results of which Yb:YAG crystals are more suitable for high-power applications. Then, the effects of the thermodynamic and spectral properties of Yb:YAG crystals with temperature were analyzed in detail, and it was shown that the laser beams amplified by the cryogenically cooled Yb:YAG crystals could have higher beam quality, higher pump absorption efficiency, lower pump threshold, and higher gain. The change in properties of Yb:YAG crystal at low temperature makes it more suitable as a gain medium for high-power lasers. Subsequently, two types of kilowatt-class lasers using cryogenically cooled Yb:YAG crystals as gain media are introduced—100 J, 10 Hz nanosecond lasers and 1 J, 1 kHz picosecond lasers. Their configuration, main parameters, and typical output results were analyzed. Finally, future directions in the development of cryogenically cooled Yb:YAG lasers are discussed. Full article

This paper presents a broadband 3–3.7 GHz class-J Doherty power amplifier exploiting second harmonic tuning in the output network. Furthermore, the output impedance inverter is eliminated and its effect is embedded in the main device’s output matching network, thus trading off among bandwidth, efficiency, and gain. The proposed amplifier adopts two 10 W packaged GaN transistors, and it achieves in measurement 60–74%, and 46–50% drain efficiency at saturation and 6 dB output back-off, respectively, with a saturated output power of 43–44.2 dBm and a small-signal gain of 10–13 dB. The proposed DPA exhibits a simulated adjacent channel power ratio less than −30 dBc at 36 dBm average output power, when a 16-QAM modulation with 5 MHz bandwidth is applied to the 3.5 GHz carrier. Full article

The operation of the power amplifier (PA) in wireless transmitters presents a trade-off between linearity and power efficiency, being more efficient when the device exhibits the highest nonlinearity. Its modeling and linearization performance depend on the quality of the underlying Volterra models that are characterized by the presence of relevant terms amongst the enormous amount of regressors that these models generate. The presence of PA mechanisms that generate an internal state variable motivates the adoption of a bivariate Volterra series perspective with the aim of enhancing modeling capabilities through the inclussion of beneficial terms. In this paper, the conventional Volterra-based models are enhanced by the addition of terms, including cross products of the input signal and the new internal variable. The bivariate versions of the general full Volterra (FV) model and one of its pruned versions, referred to as the circuit-knowledge based Volterra (CKV) model, are derived by considering the signal envelope as the internal variable and applying the proposed methodology to the univariate models. A comparative assessment of the bivariate models versus their conventional counterparts is experimentally performed for the modeling of two PAs driven by a 30 MHz 5G New Radio signal: a class AB PA and a class J PA. The results for the digital predistortion of the class AB PA under a direct learning architecture reveal the benefits in linearization performance produced by the bivariate CKV model structure compared to that of the univariate CKV model. Full article

This work develops a novel dynamic load modulation Power Amplifier (PA) circuity that can provide an optimum compromise between linearity and efficiency while covering multiple cellular frequency bands. Exploiting monolithic microwave integrated circuits (MMIC) technology, a fully integrated 1W Doherty PA architecture is proposed based on 0.1 μm AlGaAs/InGaAs Depletion-Mode (D-Mode) technology provided by the WIN Semiconductors foundry. The proposed wideband DPA incorporates the harmonic tuning Class-J mode of operation, which aims to engineer the voltage waveform via second harmonic capacitive load termination. Moreover, the applied post-matching technique not only reduces the impedance transformation ratio of the conventional DPA, but also restores its proper load modulation. The simulation results indicate that the monolithic drive load modulation PA at 4 V operation voltage delivers 44% PAE at the maximum output power of 30 dBm at the 1 dB compression point, and 34% power-added efficiency (PAE) at 6 dB power back-off (PBO). A power gain flatness of around 14 ± 0.5 dB was achieved over the frequency band of 23 GHz to 27 GHz. The compact MMIC load modulation technique developed for the 5G mobile handset occupies the die area of 3.2 mm². Full article

This work presents a strategy to upgrade models for power amplifier (PA) behavioral modeling and digital predistortion (DPD). These incomplete structures are the consequence of nonlinear order and memory depth model truncation with the purpose of reducing the demand of the limited computational resources available in standard processors. On the other hand, the alternative use of model structures pruned a priori does not guarantee that every significant term is included. To improve the limited performance of an incomplete model, a general procedure to augment its structure by incorporating significant terms is demonstrated. The sparse nature of the problem allows a successive search incorporating additional terms with higher nonlinear order and memory depth. This approach is investigated in the modeling and linearization of a commercial class AB PA operating at a compression point of about 6 dB, and a class J PA operating near saturation. Results highlight the capabilities of this upgrading procedure in the improvement of linearization capabilities of DPDs. Full article

In ultrasonic systems, power amplifiers are one of the most important electronic components used to supply output voltages to ultrasonic devices. If ultrasonic devices have low sensitivity and limited maximum allowable voltages, it can be quite challenging to detect the echo signal in the ultrasonic system itself. Therefore, the class-J power amplifier, which can generate high output power with high efficiency, is proposed for such ultrasonic device applications. The class-J power amplifier developed has a power efficiency of 63.91% and a gain of 28.16 dB at 25 MHz and 13.52 dB_m input. The pulse-echo measurement method was used to verify the performance of the electronic components used in the ultrasonic system. The echo signal appearing with the discharged high voltage signal was measured. The amplitude of the first echo signal in the measured echo signal spectrum was 4.4 V and the total-harmonic-distortion (THD), including the fundamental signal and the second harmonic, was 22.35%. The amplitude of the second echo signal was 1.08 V, and the THD, including the fundamental signal and the second harmonic, was 12.45%. These results confirm that a class-J power amplifier can supply a very high output echo signal to an ultrasonic device. Full article