Saturation Power Level Research Articles

Design of Broadband Doherty Power Amplifier Based on Misaligned Current Phase

A broadband Doherty power amplifier (DPA) always experiences an efficiency degradation between two efficiency peaks, especially at two side bands. In this study, the efficiency degradation was demonstrated to be caused caused by the in-phase power combining at the saturation power level. To solve this problem, current misalignment was introduced into the broadband DPA design. The carrier and peaking PA have different current phases when performing the power combination at the saturation power level. In this work, it was also demonstrated that the efficiency in the high-power region of a DPA can be improved by elaborately using misaligned current phases. A detailed analysis and the design procedure of a broadband DPA are presented in this paper. And a 1.5–2.45 GHz broadband DPA was implemented and measured. The fabricated DPA achieves a saturation output power of 42.7–44.9 dBm, a saturation drain efficiency (DE) of 62.7–74.1% and a gain of 10.2–13.9 dB over 1.5–2.45 GHz. Moreover, the fabricated DPA also achieves a 6 dB back-off DE of more than 49.1% in the frequency band of interest.

A 15.3-dBm, 18.3% PAE F-Band Power Amplifier in 130-nm InP HBT With Modulation Measurements

A scalable platform for modulation measurements at millimeter-and submillimeter-wave frequencies is presented and demonstrated at 121 GHz. The system is used to characterize a 130-nm InP stacked power amplifier (PA) at saturated power levels, without using digital predistortion (DPD). A peak data rate of 10 Gb/s is achieved at a peak power level of 14.1 dBm (max power added efficiency (PAE) point) and is the highest recorded data rate on stand-alone PAs at frequencies greater than 100 GHz at peak power levels greater than 10 dBm. The PA exhibits a peak gain of 11.7 dB and a 3-dB bandwidth (BW) of 45 GHz, measured from 90 to 135 GHz. The peak measured PAE and saturated output power ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\text{sat}}$</tex-math> </inline-formula> ) at 112.5 GHz are 18.3% and 15.3 dBm, respectively.

In vivo pH mapping with omega plot-based quantitative chemical exchange saturation transfer MRI.

Chemical exchange saturation transfer (CEST) MRI is promising for detecting dilute metabolites and microenvironment properties, which has been increasingly adopted in imaging disorders such as acute stroke and cancer. However, in vivo CEST MRI quantification remains challenging because routine asymmetry analysis (MTRasym ) or Lorentzian decoupling measures a combined effect of the labile proton concentration and its exchange rate. Therefore, our study aimed to quantify amide proton concentration and exchange rate independently in a cardiac arrest-induced global ischemia rat model. The amide proton CEST (APT) effect was decoupled from tissue water, macromolecular magnetization transfer, nuclear Overhauser enhancement, guanidinium, and amine protons using the image downsampling expedited adaptive least-squares (IDEAL) fitting algorithm on Z-spectra obtained under multiple RF saturation power levels, before and after global ischemia. Omega plot analysis was applied to determine amide proton concentration and exchange rate simultaneously. Global ischemia induces a significant APT signal drop from intact tissue. Using the modified omega plot analysis, we found that the amide proton exchange rate decreased from 29.6 ± 5.6 to 12.1 ± 1.3s-1 (P < 0.001), whereas the amide proton concentration showed little change (0.241 ± 0.035% vs. 0.202 ± 0.034%, P=0.074) following global ischemia. Our study determined the labile proton concentration and exchange rate underlying the in vivo APT MRI. The significant change in the exchange rate, but not the concentration of amide proton demonstrated that the pH effect dominates the APT contrast during tissue ischemia.

Ratiometric chemical exchange saturation transfer pH mapping using two iodinated agents with nonequivalent amide protons and a single low saturation power.

As an essential physiological parameter, pH plays a critical role in maintaining cellular and tissue homeostasis. The ratiometric chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) method using clinically approved iodinated agents has emerged as one of the most promising noninvasive techniques for pH assessment. In this study, we investigated the ability to use the combination of two different nonequivalent amide protons, chosen from five iodinated agents, namely iodixanol, iohexol, iobitridol, iopamidol, and iopromide, for pH measurement. The ratio of two nonequivalent amide CEST signals was calculated and compared for pH measurements in the range of 5.6 to 7.6. To quantify the CEST signals at 4.3 and 5.5 parts per million (ppm), we employed two analytic methods: magnetization transfer ratio asymmetry and Lorentzian fitting analysis. Lastly, the established protocol was used to measure the pH values in healthy rat kidneys (n=5). The combination of iodixanol and iobitridol at a ratio of 1:1 was found to be suitable for pH mapping. The saturation power level (B1) was also investigated, and a low B1 of 1.5 µT was adopted for subsequent pH measurements. Improved precision and an extended pH detection range were achieved using iodixanol and iobitridol (1:1 ratio) and a single low B1 of 1.5 µT in vitro. In vivo renal pH values were measured as 7.23±0.09, 6.55±0.15, and 6.29±0.23 for the cortex, medulla, and calyx, respectively. These results show that the ratiometric CEST method using two iodinated agents with nonequivalent amide protons could be used for in vivo pH mapping of the kidney under a single low B1 saturation power.

Impact of Nonideal Auxiliary Current Profile on Linearity of Microwave Doherty Amplifiers: Theory and Experiments

A new nonlinear effect of Doherty power amplifier (DPA) caused by the nonideal auxiliary current is disclosed. In contrary to traditional assumption, the auxiliary current profile is found to be a nonlinear function of input drive. Although perfect load modulation conditions can be enforced at the transition and saturation power levels (i.e., two efficiency peaks), inside the Doherty region, the nonlinear auxiliary current incurs insufficient load modulation, leading to voltage clipping effect. Theoretical analysis reveals that the conventional design (DPA-I) can suffer from degraded linearity performance with distorted waveforms, increased harmonic regrowth, and poor phase distortion. For further investigation, a modified design (DPA-II) is contrived with remedied clipping effect. Simulation studies show that the linearity of DPA-II is largely improved with minimal reduction in efficiency, which indicates this non-ideal current profile is one of the fundamental limiting factors of DPA linearity and cannot be overlooked. For verification, two 42-dBm 2-GHz symmetrical DPAs based on GaN HEMT are designed, fabricated, and measured. Experimental results show that DPA-II provides 11-dB suppression in third-order intermodulation distortion (IMD3) and 8-dB enhancement in adjacent channel leakage power ratio (ACLR), compared to DPA-I. Meanwhile, excellent efficiency performance was attained with drain efficiency of 54%/71.5% at back-off/saturation.

Assessment of Early Response to Neoadjuvant Systemic Therapy in Triple-Negative Breast Cancer Using Amide Proton Transfer–weighted Chemical Exchange Saturation Transfer MRI: A Pilot Study

Purpose To determine if amide proton transfer-weighted chemical exchange saturation transfer (APTW CEST) MRI is useful in the early assessment of treatment response in persons with triple-negative breast cancer (TNBC). Materials and Methods In this prospective study, a total of 51 participants (mean age, 51 years [range, 26-79 years]) with TNBC were included who underwent APTW CEST MRI with 0.9- and 2.0-µT saturation power performed at baseline, after two cycles (C2), and after four cycles (C4) of neoadjuvant systemic therapy (NAST). Imaging was performed between January 31, 2019, and November 11, 2019, and was a part of a clinical trial (registry number NCT02744053). CEST MR images were analyzed using two methods-magnetic transfer ratio asymmetry (MTRasym) and Lorentzian line shape fitting. The APTW CEST signals at baseline, C2, and C4 were compared for 51 participants to evaluate the saturation power levels and analysis methods. The APTW CEST signals and their changes during NAST were then compared for the 26 participants with pathology reports for treatment response assessment. Results A significant APTW CEST signal decrease was observed during NAST when acquisition at 0.9-µT saturation power was paired with Lorentzian line shape fitting analysis and when the acquisition at 2.0 µT was paired with MTRasym analysis. Using 0.9-µT saturation power and Lorentzian line shape fitting, the APTW CEST signal at C2 was significantly different from baseline in participants with pathologic complete response (pCR) (3.19% vs 2.43%; P = .03) but not with non-pCR (2.76% vs 2.50%; P > .05). The APTW CEST signal change was not significant between pCR and non-pCR at all time points. Conclusion Quantitative APTW CEST MRI depended on optimizing acquisition saturation powers and analysis methods. APTW CEST MRI monitored treatment effects but did not differentiate participants with TNBC who had pCR from those with non-pCR. © RSNA, 2021 Clinical trial registration no. NCT02744053 Supplemental material is available for this article. Keywords Molecular Imaging-Cancer, Molecular Imaging-Clinical Translation, MR-Imaging, Breast, Technical Aspects, Tumor Response, Technology Assessment.

Abstract PS3-08: Assessment of early response to neoadjuvant systemic therapy (NAST) of triple-negative breast cancer (TNBC) using chemical exchange saturation transfer (CEST) MRI: A pilot study

Abstract PS3-08: Assessment of early response to neoadjuvant systemic therapy (NAST) of triple-negative breast cancer (TNBC) using chemical exchange saturation transfer (CEST) MRI: A pilot study

Single-Chip CMOS Reconfigurable Dual-Band Tri-Mode High-Efficiency RF Amplifier Design

This brief presents a new design methodology of single-chip reconfigurable CMOS RF power amplifier (PA) supporting both dual-band and multi-power-mode operation. The proposed architecture utilizes a novel switched-capacitor based output network to facilitate differential signal combining and impedance transformation at two widely separated frequency bands. It can offer three distinct output power levels (saturation) to be selected for multi-power-mode applications. Besides, closed-form explicit equations are readily available for the evaluation of component values. For verification, a PA operating at 1.8/2.6 GHz (non-concurrent), with three distinct saturation power levels (21, 23, 26 dBm) and peak efficiency of about 30%, is designed and fabricated using 0.35 μm CMOS process.

Amide proton transfer (APT) imaging of parotid tumors: Differentiation of malignant and benign tumors

PurposeTo assess the usefulness of amide proton transfer (APT) imaging in differentiating parotid tumors. Material and methodsWe retrospectively analyzed 43 histopathologically proven parotid solid tumors with diameters ≥2 cm. Twenty-one tumors were benign and 12 tumors were malignant. Two-dimensional APT imaging was performed using a saturation pulse with a duration of 2 s and a saturation power level of 2 μT. For acquiring Z-spectra, the imaging was repeated at 25 saturation frequency offsets from ω = −6 to +6 ppm with a step of 0.5 ppm as well as one scan acquired far off-resonance (−1560 ppm) for signal normalization. For the APT imaging, the asymmetry analysis at 3.5 ppm downfield from the water signal was calculated. The mean APT signal intensity (SI) was compared between the benign and malignant tumors. ResultsThe mean APT SI was 2.23 ± 0.80 % in the benign tumors and significantly higher at 2.99 ± 0.99 % in the malignant tumors (P = 0.01). A receiver operating curve analysis revealed that the optimal APT SI threshold was 2.40 for distinguishing malignant tumors from benign tumors with an area under the curve of 0.74. The sensitivity, specificity, and accuracy were 83.3%, 61.3%, and 67.4%, respectively. ConclusionThe mean APT SI of the malignant parotid tumors was significantly higher than that of the benign parotid tumors.

A 28-GHz Beamforming Doherty Power Amplifier With Enhanced AM-PM Characteristic

This article presents a beamforming Doherty power amplifier (B-DPA) for the 28-GHz fifth-generation (5G) new-radio band. The proposed B-DPA is based on a new combiner topology that allows the current profile in the auxiliary branch of the DPA to be relaxed while simultaneously canceling the amplitude-to-phase (AM-PM) distortion exhibited in the active devices. This approach enables efficiency and linearity enhancements. In addition, the DPA is augmented with high-accuracy digitally assisted vector multipliers at its input stage to provide the required relative and absolute phase adjustments for proper Doherty operation and the overall phase shift required for beamforming. A proof-of-concept prototype was implemented in the 45-nm silicon on insulator (SOI)-CMOS technology. Measurement results reveal that the proposed B-DPA demonstrated good Doherty operation with drain efficiencies of 18%–20% and 33%–35% at 6-dB back-off and saturation power (Psat, 18 dBm) levels, respectively, between 28 and 30 GHz. In particular, excellent AM-PM characteristics were noted with a peak value of only 1.5° up to Psat, which remained below 2.5° as the B-DPA was swept with a 0° to 360° phase shift. Finally, modulated-signal tests revealed error vector magnitudes of 3.1% and 0.9% for 4-MHz $\times100$ -MHz orthogonal frequency division multiplexing (OFDM) signals before and after applying digital predistortion, respectively.

Design of continuous mode Doherty power amplifiers using generalized output combiner

In this paper, a continuous mode Doherty power amplifier (DPA) working over an octave bandwidth is constructed using a generalized combiner. The generalized combiner provides the PA designers with more freedoms for realizing broadband DPAs. Theoretically, the generalized combiner could expand the working bandwidth of continuous mode DPA. A continuous mode DPA working over 1.2–2.7 GHz (a relative bandwidth of 76.9%) is implemented in this contribution for demonstrating the universality of the generalized combiner. As a demonstrator circuit, the fabricated DPA achieves drain effciencies of 40–54% and 44–75% at 6 dB back-off and saturation power levels, respectively. The maximum output power of the fabricated DPA is 42.1–44.2 dBm with a saturation gain of 7.2–11.3 dB over 1.2–2.7 GHz. When the designed DPA is excited by a 20 MHz LTE signal with a peak to average power ratio of 7.04 dB, the fabricated DPA achieves adjacent channel leakage ratios (ACLRs) of −29.5 dBc and −49.5 dBc at 2.4 GHz before and after DPD technique, respectively.

A 4–32 GHz SiGe Multi-Octave Power Amplifier With 20 dBm Peak Power, 18.6 dB Peak Gain and 156% Power Fractional Bandwidth

This letter presents the design and characterization results of a multi-octave power amplifier (MOPA) fabricated in a 0.13- $\mu \text{m}$ SiGe-BiCMOS technology. The single-stage power amplifier is implemented as the stack of a cascode amplifier combining broadband input matching network with resistive feedback, and a common-base amplifier with base capacitive feedback. Measurement results show that the design delivers a peak saturated output power level of 20.2 dBm, with output of 1 dB compression at 19.4 dBm. The measured 3-dB power bandwidth is from 4 to 32 GHz, covering three octaves. The corresponding power fractional bandwidth (PFBW) is 156%. The measured peak power added efficiency is 20.6%, and peak small-signal gain is 18.6 dB. The fabricated integrated circuit occupies an area of 0.71 mm2. To compare state-of-the-art MOPAs, the power amplifier figure of merit defined by the international technology roadmap for semiconductors (ITRS) is modified to include PFBW and area. To the best of authors’ knowledge, the presented design achieves the highest figure of merit among multi-octave PAs in a silicon-based integrated circuit technology reported in the literature.

Harmonic‐tuned continuum mode active load modulation output combiner for the design of broadband asymmetric Doherty power amplifiers

The conventional Doherty output combiner limits the bandwidth of operation in the asymmetric Doherty power amplifiers (DPAs). In this study, an output combiner that is designed using a harmonic-tuned continuum mode active load modulation technique is proposed with the main target of extending the bandwidth of operation in the asymmetric DPAs. Through this methodology, design equations are derived and multiple harmonic impedance solutions are provided. This offers greater freedom for designing the output combiner of the asymmetric DPA which consists of the impedance inverting network and the impedance transforming network. Moreover, enhancements in the efficiencies at back-off and saturation power levels are made possible. The efficacy of the design strategy is demonstrated by the realised broadband asymmetric DPA prototype working within the band of 1.4–2.45 GHz. The experimental results have shown 54.55% bandwidth of operation, accounting for about 0.95–12.55% increment in bandwidth as compared with some recently published DPAs in the literature. Substantially, drain efficiencies within 35.5–52% at 6 dB output power back-off level and 47.5–64.2% at peaking power level are also recorded from the experiments. The maximum output power and gain are recorded at 43.52 dBm and 13.03 dB, respectively.

Design of Concurrent Dual-Band Continuous Class-J Mode Doherty Power Amplifier With Precise Impedance Terminations

In this letter, a novel methodology for designing concurrent dual-band continuous class-J mode Doherty power amplifier (DPA) with precise impedance terminations is presented. First, the required impedance condition of the carrier amplifier which operates in continuous class-J mode at the back-off region is analyzed in detail. Based on the proposed theory, the fundamental impedance is realized by taking advantage of the noninfinity output impedance of the peaking stage, then the second harmonic impedance is realized with a harmonic tuning postmatching network. A 1.8-/2.6-GHz dual-band DPA employing commercial GaN devices is designed and implemented to validate the proposed method. The fabricated DPA can achieve 68.5% and 75% drain efficiencies (DEs) for saturated power level at 1.8 and 2.6 GHz, respectively. For the 6-dB back-off region, the measured DEs are 64% and 63% at the two designed frequencies.

Bandwidth Extension of Doherty Power Amplifier Using Complex Combining Load With Noninfinity Peaking Impedance

In this paper, a high-efficiency Doherty power amplifier (DPA) using the complex combining load (CCL) with noninfinity peaking impedance for broadband operation is presented. By applying the CCL, the load impedance of the carrier amplifier at saturation power level can be compensated at different operation frequencies. Considering the influences of the output impedance of the peaking PA on the carrier PA, a detailed analysis of the optimal noninfinity peaking output impedance with the CCL is carried out on the whole operation frequency range. Theoretical analysis of the output power and drain efficiency (DE) reveals that the CCL can offer a new degree of freedom for extending the bandwidth of the DPA. Based on the proposed theory, a modified DPA working over the frequency band of 1.1-2.4 GHz (bandwidth of 74%) is designed and fabricated based on GaN HEMT devices. Experimental results exhibit 6-dB output back-off drain efficiencies of 43.8%-54.9% and saturated drain efficiencies of 55.4%-68% can be obtained. The saturated output power of the DPA is 43.3-45.4 dBm with a gain of 9.5-11.1 dB across the whole operation band. When driven with long-term evolution modulated signals with 6.5-dB peak-to-average power ratio, the DPA exhibits an adjacent channel leakage ratio better than -49 dBc while maintaining a DE of 44% after digital predistortion linearization.

Temperature Stabilization of the Klystron Cooling Water at the KOMAC

A total of nine klystrons each with a high peak power are used to deliver RF power to the 100 MeV proton linac at the Korea Multi-purpose Accelerator Complex (KOMAC). We found that the temperature of the cooling water to the klystron cavity was deeply related to the RF power output from the klystron when the klystron was operated either in the open loop mode or at a saturation power level. To stabilize the RF power from the klystron, we need to stabilize the cooling water’s temperature as much as possible. To keep the cooling water’s temperature constant, we used an inverter-driven cooling fan at the cooling tower with proportional integral derivative (PID) controller. Through a proper tuning of the control parameters, we could suppress the temperature fluctuation to within ±0.2 °C and stabilize the output RF power from the klystron, regardless of the ambient temperature. Details on the dependency of the output RF power on the coolant temperature and stabilization method will be given in this paper.

Influences of experimental parameters on chemical exchange saturation transfer (CEST) metrics of brain tumors using animal models at 4.7T.

To investigate the dependence of magnetization transfer ratio asymmetry at 3.5 ppm (MTRasym (3.5 ppm)), quantitative amide proton transfer (APT# ), and nuclear Overhauser enhancement (NOE# ) signals or contrasts on experimental imaging parameters. Modified Bloch equation-based simulations using 2-pool and 5-pool exchange models and in vivo rat brain tumor experiments at 4.7T were performed with varied RF saturation power levels, saturation lengths, and relaxation delays. The MTRasym (3.5 ppm), APT# , and NOE# contrasts between tumor and normal tissues were compared among different experimental parameters. The MTRasym (3.5 ppm) image contrasts between tumor and normal tissues initially increased with the RF saturation length, and the maxima occurred at 1.6-2 s under relatively high RF saturation powers (>2.1 μT) and at a longer saturation length under relatively low RF saturation powers (<1.3 μT). The APT# contrasts also increased with the RF saturation length but peaked at longer RF saturation lengths relative to MTRasym (3.5 ppm). The NOE# contrasts were either positive or negative, depending on the experimental parameters applied. Tumor MTRasym (3.5 ppm), APT# , and NOE# contrasts can be maximized at different saturation parameters. The maximum MTRasym (3.5 ppm) contrast can be obtained with a relatively longer RF saturation length (several seconds) at a relatively lower RF saturation power.

Flip-angle based ratiometric approach for pulsed CEST-MRI pH imaging

Several molecules have been exploited for developing MRI pH sensors based on the chemical exchange saturation transfer (CEST) technique. A ratiometric approach, based on the saturation of two exchanging pools at the same saturation power, or by varying the saturation power levels on the same pool, is usually needed to rule out the concentration term from the pH measurement. However, all these methods have been demonstrated by using a continuous wave saturation scheme that limits its translation to clinical scanners. This study shows a new ratiometric CEST-MRI pH-mapping approach based on a pulsed CEST saturation scheme for a radiographic contrast agent (iodixanol) possessing a single chemical exchange site. This approach is based on the ratio of the CEST contrast effects at two different flip angles combinations (180°/360° and 180°/720°), keeping constant the mean irradiation RF power (Bavg power). The proposed ratiometric approach index is concentration independent and it showed good pH sensitivity and accuracy in the physiological range between 6.0 and 7.4.

Investigation of Saturation Effects in Ceramic Phosphors for Laser Lighting.

We report observations of saturation effects in a Ce:LuAG and Eu-doped nitride ceramic phosphor for conversion of blue laser light for white light generation. The luminous flux from the phosphors material increases linearly with the input power until saturation effects limit the conversion. It is shown that the temperature of the phosphor layer influences the saturation power level and the conversion efficiency. It is also shown that the correlated color temperature (CCT), phosphor conversion efficiency and color rendering index (CRI) are dependent both on the incident power and spot size diameter of the illumination. A phosphor conversion efficiency up to 140.8 lm/W with CRI of 89.4 was achieved. The saturation in a ceramic phosphor, when illuminated by high intensity laser diodes, is estimated to play the main role in limiting the available luminance from laser-based lighting systems.

The Influence of the Output Impedances of Peaking Power Amplifier on Broadband Doherty Amplifiers

The effect of the output impedance of peaking power amplifier (PA) on Doherty PAs (DPAs) is analyzed in this paper. In the design procedure of DPAs, the ideal case is that the output impedance of auxiliary PA is infinite at output power back-off (OPBO) level. However, it is almost impossible to realize this perfect condition in broadband DPAs. Therefore, when the output impedance of peaking path deviates from infinity, some potential effects on DPAs must be produced. In this paper, these effects are explained at the internal plane of transistors. The conclusion is that, at different normalized frequencies, there are different optimal impedance regions for the output impedance of peaking stage. This means that the noninfinite output impedances of peaking stage can enhance the performances of broadband DPAs so long as they are elaborately processed. A 1.65–2.7-GHz (48% bandwidth) broadband DPA is designed considering the effects of peaking PA. The experimental results show that this DPA obtains a drain efficiency of 41%–59.6% at 6-dB OPBO levels and a drain efficiency of 55.8%–72.2% at saturation power levels. The maximum output power across the entire operating band is 43.1–45.2 dBm with a gain of 9.0–10.2 dB. Furthermore, the designed DPA achieves an adjacent channel leakage ratio of −45.8 dBc with an output power of 36.1 dBm at 2.0 GHz after digital predistortion when it is excited by 5-MHz WCDMA signal with a peaking-to-average power ratio of 8.6 dB.