A new approach for a phase controlled self-oscillating mixer

The analytical and experimental demonstration of subharmonic synchronization and phase shifting of a push-pull self-oscillating mixer is presented for the first time. Inherent high mixing gain of the self-oscillating mixer circuit is exploited to generate a strong signal at the same frequency of the reference signal, which is related to the local oscillator's (LO) phase information. A phase error between this signal and the reference signal is extracted in a phase comparator before phase locking. Analytical modeling of frequency and phase stabilization of the push-pull self-oscillating mixer is presented, which is also experimentally verified for a self-oscillating mixer at 12 GHz. This self-oscillating mixer circuit demonstrates efficient phase locking, 0°-180° continuous phase shifting capability in addition to the reported large locking range (>10 MHz), low close-in to carrier phase noise (<7 dB degradation of a 6 GHz synthesized reference signal), and a high mixer conversion gain (>17 dB at 17 GHz). The demonstrated subharmonic phase locking approach replaces the need for a frequency multiplier or divider before the phase comparator. The synchronized push-pull self-oscillating mixer circuit is applicable to the millimeter-wave frequency distributed transmitters and receivers, where low-loss phase shifting and efficient subharmonic phase and frequency locking are hard to achieve     

Sub‐Millimeter‐Scale Monolayer p‐Type H‐Phase VS2

2D H‐phase vanadium disulfide (VS₂) is expected to exhibit tunable semiconductor properties as compared with its metallic T‐phase structure, and thus is of promise for future electronic applications. However, to date such 2D H‐phase VS₂ nanostructures have not been realized in experiment likely due to the polymorphs of vanadium sulfides and thermodynamic instability of H‐phase VS₂. Preparation of H‐phase VS₂ monolayer with lateral size up to 250 µm, as a new member in the 2D transition metal dichalcogenides (TMDs) family, is reported. A unique growth environment is built by introducing the molten salt‐mediated precursor system as well as the epitaxial mica growth platform, which successfully overcomes the aforementioned growth challenges and enables the evolution of 2D H‐phase structure of VS₂. The honeycomb‐like structure of H‐phase VS₂ with broken inversion symmetry is confirmed by spherical aberration‐corrected scanning transmission electron microscopy and second harmonic generation characterization. The phase structure is found to be ultra‐stable up to 500 K. The field‐effect device study further demonstrates the p‐type semiconducting nature of the 2D H‐phase VS₂. The study introduces a new phase‐stable 2D TMDs materials with potential features for future electronic devices.     

Adaptive nulling in monopulse antennas

Theoretical and experimental results are presented for phase-only nulling in low-sidelobe monopulse antennas. Both results are based on a gradient search algorithm that simultaneously searches for a minimum in the sum and difference channel output powers. The array's beam steering phase shifters double as the adaptive weights. Each element in the gradient is found by changing phase shifter setting by ΔΨ (the phase shifter stepsize) and measuring the change in output power. Then the phase shifter is restored to its original value, and the process repeated for all the remaining array phase shifters. The algorithm iterates as long as each new adaptive weight setting reduces the total output power. If the output does not go down, then ΔΨ is decremented by one setting and the iteration is started again. The algorithm stops when ΔΨ=0. The adaptive weights act as random perturbations to the phase taper of the array. Consequently, the sidelobe level is proportional to the size of the phase perturbations and inversely related to the number of elements. By keeping the adaptive phase shifts small, the average sidelobe level and the main beam gain do not drastically change     

Design considerations for integrated CMOS reflective-type phase shifters

An analysis of reflective-type phase shifters with transformed single-resonant loads for integrated CMOS phased-array implementations is presented. Several components of the standard lumped-element coupler can be eliminated without significant performance degradation, to allow more compact implementations. It is found that the varactor should be chosen as small as feasible to minimize sensitivity to parasitic resistance. Larger varactors reduce sensitivity to parasitic capacitance, but this can be compensated for in the phase shifter design. A general design procedure for reflective-type phase shifters is given. A phase shifter operating at 2.0 GHz has been designed and implemented in a 0.18 μm CMOS process using the design procedures outlined, and it occupies an area of 0.75 mm² and consumes 6.8 mW of power. The measured phase shift range is 308° for a control voltage varying from 0–1.8 V, which to our knowledge is the largest phase shift range of any CMOS reflective-type phase shifter reported to date.     

基于液晶空间光调制器的相位差波前探测技术定量研究

为了定量研究相位差波前探测技术(phase diversity technique,PD)对波前探测和图像重建的精度,本文分别进行了数值模拟以及相关实验。数值模拟中采用了均方根(root-mean-square,RMS)分别为0.1λ~0.5λ的五组随机畸变波前,获得其退化的焦面图像和相应的离焦图像信息,利用PD技术对其进行波前探测和图像重建,波前探测的残余误差RMS值均达到了10~(-5)λ水平,重建图像在分辨率和对比度上有明显提升。搭建了基于液晶空间光调制器的实验系统,利用液晶空间光调制器来定量施加随机的波前像差,可以有效解决湍流屏数据难以量化的问题。同样将PD技术应用于本实验所采集到的退化焦面图像和相应离焦图像,对于RMS值为0.306λ的随机波前像差,探测波前的残余误差为0.091λ,图像重建结果与模拟结果高度一致,本文列举并分析了可能造成实验误差的多种因素,同时为该技术应用于液晶系统积累了技术基础。     

Design of novel wideband reflective phase shifters with wide range of phase applications

This paper presents wideband compact differential reflective phase shifter based on the double layer slot-coupled coupler configuration. This novel phase shifter arrangement consists of a 3-dB hybrid coupler with the coupled and transmission ports terminated with rectangular and elliptically shaped microstrip loads. By altering the ports termination of the coupler, phase shifters propose differential phase ranging from −90° to +90° over 1.3–5.9G Hz frequency band. To achieve different range of phase performance, the proper reactance is calculated at the outputs of coupler. These reactances are transformed to the elliptical or rectangular-shaped microstrip load with various dimensions for every phase shifter. The calculation and simulations results show that the developed circuits could provide ±30°, ±60°, ±45° and ±90° differential phase shifts. For verification of this wideband phase shifter design method, two phase shifter example with rectangular and elliptical load termination is fabricated and measured. The measured return loss of the phase shifter with elliptically load is better than 10 dB over 1.3–5.9G Hz frequency band as well as insertion loss is less than 1 dB. The phase shift deviation is less than 2.1°. The results demonstrate that the proposed phase shifters are well suited for use in GPS/LTE/WiMax/WLAN frequency bands.     

Images of a First‐Order Spin‐Reorientation Phase Transition in a Metallic Kagome Ferromagnet

First‐order phase transitions, where one phase replaces another by virtue of a simple crossing of free energies, are best known between solids, liquids, and vapors, but they also occur in a wide range of other contexts, including even elemental magnets. The key challenges are to establish whether a phase transition is indeed first order, and then to determine how the new phase emerges because this will determine thermodynamic and electronic properties. Here it is shown that both challenges are met for the spin reorientation transition in the topological metallic ferromagnet Fe₃Sn₂. The magnetometry and variable temperature magnetic force microscopy experiments reveal that, analogous to the liquid–gas transition in the temperature–pressure plane, this transition is centered on a first‐order line terminating in a critical end point in the field‐temperature plane. The nucleation and growth associated with the transition is directly imaged, indicating that the new phase emerges at the most convoluted magnetic domain walls for the high temperature phase and then moves to self‐organize at the domain centers of the high temperature phase. The dense domain patterns and phase coexistence imply a complex inhomogenous electronic structure, which can yield anomalous contributions to the electrical conductivity.     

溶液PH值对CdS薄膜结构特性的影响

采用化学水浴沉积(CBD)工艺在玻璃衬底上制 备CdS薄膜,研究溶液PH值对CdS 薄膜结构特性的影响。薄膜的厚度、组份、晶相结构和表观形貌分别由台阶仪、X射线荧光 光谱(XRF)、X射线衍射(XRD)和场发射扫描电子显微镜(FESEM)来表征。溶液的 PH值为11.26、 11.37和11.48时,CdS薄膜的晶相以六方相为主,薄膜的厚度先增大后减小; PH值为11.62、11.66时,薄膜的晶相以立方相为主,薄 膜的厚度进一步减小。同时,随着溶液PH值 增大,CdS薄膜的晶格常数也逐渐增大。两种晶相的CdS薄膜缓冲层与CIGS薄膜分别构成异 质 对形成异质结时的晶格失配分别为32.297%和1.419%,界面态密度分别为2.792×10¹⁴和8.507×10¹²,因此高效CIGS薄 膜太阳电池更需要立方相的CdS薄膜。     

Phase calibration of polarimetric radars from slightly roughsurfaces

The phase calibration problem for polarimetric radars is discussed. More specifically, the assumption that the copolar vertical and horizontal returns from a slightly rough surface are in phase is critically reviewed. It is concluded by means of a theoretical analysis that the phase difference for moist soil targets can reach up to 10° at 15 GHz and for incidence angles of 50°. However the assumption of zero phase difference is a good approximation for dry soils, lower frequencies, and low incidence angles     

Sensitivity degradation of an optical {2×2} and a {3×3}phase diversity ASK receiver due to gain imbalance and nonideal phaserelations of the optical hybrid

The sensitivity penalty due to phase and gain imbalance for a {2×2} and a {3×3} optical homodyne phase diversity amplitude-shift keying (ASK) receiver is investigated for the shot-noise-limited case. It is shown that both types of imbalance lead to a time varying character of the bit error rate (BER) types of imbalance and the phase mismatch. The calculation of the BER is performed as a function of the threshold value. It is shown that for an optimized threshold value, the phase diversity ASK receivers can tolerate rather large amounts of gain imbalance, namely approximately ±10%, and a phase mismatch of approximately ±10° for the {2×2} receiver and approximately ≠15° for the {3×3} receiver without an excessive sensitivity degradation (<2 dB)     

Discrete Time Analyses of Nonuniform Sampling First- and Second-Order Digital Phase Lock Loops

The present paper considers discrete time analyses of firstand second-order digital phase lock loops. These loops are characterized by the fact that they track the zero crossings of the incoming signal; consequently, the sampling intervals are nonuniform. The firstorder loop is analyzed for phase step and frequency step inputs; mean time to skip cycle is also considered. For phase step input, approximate expressions are obtained for the steady-state phase error probability density and phase error variance, the second of which leads directly to a theoretical prediction of threshold. The second-order loop is analyzed for frequency step input. Approximate expressions for the steady-state phase error probability density, phase error variance, and a theoretical prediction of threshold are obtained. The analyses are confirmed by numerical results and simulation.     

Phase-correcting feedback system for class E power amplifier

A phase-correcting feedback system which reduces the AM-to-PM distortion of Class E power amplifiers for wireless communication is presented in this paper. It comprises a novel limiting amplifier, a phase detector, and a phase shifter all operating at 835 MHz. The phase-correcting feedback together with a Class E power amplifier were fabricated in a 0.8-μm GaAs MESFET process. The limiting amplifier has a phase error less than 2.5°. The phase detector and phase shifter have a sensitivity of 10 mV/degree and 80°/V, respectively. The Class E power amplifier delivers 26.5 dBm to the load with a power added efficiency of 67%. The phase correcting feedback system reduces the 30° phase distortion of the Class E amplifier down to 4°, and its total power dissipation is 21.5 mW     

An X-band 22.5°/45° digital phase shifter based on switched filter networks

The design approach and performance of a 22.5°/45°digital phase shifter based on a switched filter network for X-band phased arrays are described. Both the MMIC phase shifters are fabricated employing a 0.25μm gate GaAs pHEMT process and share in the same chip size of 0.82×1.06 mm². The measurement results of the proposed phase shifters over the whole operating frequency range show that the phase shift error is less than 22.5°±2.5°, 45°±3.5°, which shows an excellent agreement with the simulated performance, the insertion loss is within the range of 0.9-1.2 dB for the 22.5°phase shifter and 0.9-1.4 dB for the 45°phase shifter, and the input/output return loss is better than -12.5 and -11 dB respectively. They also achieve the similar P_1dB continuous wave power handing capability of 24.8 dBm at 10 GHz. The phase shifters show a good phase shift error, insertion loss and return loss in the X-band (40%), which can be employed into the wide bandwidth multi-bit digital phase shifter.     

The Roles of the Ge‐Te Core Network and the Sb‐Te Pseudo Network During Rapid Nucleation‐Dominated Crystallization of Amorphous Ge2Sb2Te5

Ge₂Sb₂Te₅ (GST) has demonstrated its outstanding importance among rapid phase‐change (PC) materials, being applied for optical and electrical data storage for over three decades. The mechanism of nanosecond phase change in GST, which is vital for its application, has long been disputed: various, quite diverse scenarios have been proposed on the basis of various experimental and theoretical approaches. Nevertheless, one central question still remains unanswered: why is amorphous GST stable at room temperature for long time while it can rapidly transform to the crystalline phase at high temperature? Here it is revealed for the first time, by modelling the amorphous structure based on synchrotron radiation anomalous X‐ray scattering data, that germanium and tellurium atoms form a “core” Ge‐Te network with ring formation. It is also suggested that the Ge‐Te network can stabilize the amorphous phase at room temperature and can persist in the crystalline phase. On the other hand, antimony does not contribute to ring formation but constitutes a “pseudo” network with tellurium, in which the characteristic Sb–Te distance is somewhat longer than the covalent Sb–Te bond distance. This suggests that the Sb‐Te pseudo network may act as a precursor to forming critical nuclei during the crystallization process. The findings conclude that the Ge‐Te core network is responsible for the outstanding stability and rapid phase change of the amorphous phase while the Sb‐Te pseudo network is responsible for triggering critical nucleation.     

Modulation characteristics of semiconductor Mach-Zehnder opticalmodulators

The transmission and chirp characteristics are described for two types of semiconductor Mach-Zehnder modulators, distinguished by the differential phase shift between the two arms of the interferometer in the unbiased state. The conventional modulator has a differential phase shift of 0 radians, while the π-shift modulator has a differential phase shift of π radians. The nonlinear dependence on the applied voltage of the attenuation and phase constants of the optical signal propagating in the p-i-n waveguide leads to different characteristics for the two modulators. The influence of the splitting ratio of the Y-junctions is considered for single-arm and dual-arm (push-pull) modulation formats. The π-shift modulator is shown to yield better transmission performance for 10 Gb/s systems compared to the conventional modulator     

Interferometric measurement of lateral phase profile and thermallensing in broad-area diode amplifiers

A Mach-Zehnder imaging interferometric is used to directly measure the lateral phase profile in the near field of broad-area semiconductor optical amplifiers with λ/25 phase resolution, or 0.1°C in temperature. The quadratic thermally induced phase distortion and its equivalent thermal lens focal length are characterized. Anomalous localized phase variations are correlated to thermal bond nonuniformities in devices mounted under nonoptimal conditions. It is demonstrated for an unbiased 600-μm-wide by 1000-μm-long amplifier device that a phase uniformity across the stripe of better than λ/25 can be obtained     

Phase Equilibria of the Sn-V System and Interfacial Reactions in Sn/V Couples

Sn-V alloys were prepared for a phase equilibrium study at 600°C and 250°C. All alloys were annealed for longer than 6 months to ensure that they reached equilibrium. There are two intermetallic compounds, namely VSn₂ (V₂Sn₃) and V₃Sn phases. The composition of the VSn₂ phase is Sn-34.0at.%V. The VSn₂ phase has the CuMg₂ structure. It was previously designated as the V₂Sn₃ phase and was renamed in this study to be consistent with its structure and composition. The composition of the V₃Sn phase is Sn-78.0at.%V, and it has the A15 structure at 600°C and 250°C. With the new experimental results, the Sn-V system has been thermodynamically assessed with the CALPHAD approach. The calculated Sn-V phase diagram is in good agreement with the experimental determinations. Sn/V interfacial reactions at 950°C and 600°C are also examined in this study. The V₃Sn phase is formed at 950°C, while the VSn₂(V₂Sn₃) phase is formed at 600°C.     

Digital Test Method for Embedded Converters with Unknown-Phase Harmonics

This paper presents an extension of the ANC (“Analogue Network of Converters”)-based method, which is an original Design-for-Test (DfT) technique associated to a dedicated test algorithm to characterize the harmonic components of a set of embedded converters using only digital test resources. The ANC-based method was primarily developed under the assumption that the harmonics’ phase is proportional to the input phase. This assumption is not valid for all converter architectures, where filtering effects may affect the harmonics’ phase. The improved ANC-based method is able to calculate the magnitude of the harmonic components with unknown phase. The fundamental principle of this improved version of the ANC-based method is the same, but further mathematical developments have been established using a model independent from the harmonics’ phase. The simulation results and the experiments show an excellent agreement between the values measured using the method and the values measured with a usual test setup, for the THD and SFDR parameters. Simulations were carried out considering both random phases and realistic phase delays such as the ones induced by a low pass filter.     

Phase-noise analysis of MEMS-based circuits and phase shifters

The effect of Brownian, acceleration, acoustic, and power-supply noise on MEMS based circuits has been calculated for MEMS.-based circuits (phase shifters, delay circuits). The calculations are done for capacitive shunt MEMS switches and metal-to-metal contact series MEMS switches. It is found that these effects result in both an amplitude and phase noise, with the phase noise being around 100× larger than the amplitude noise. The phase noise due to Brownian motion is negligible for MEMS switches with k ≃ 1.0 N/m, g₀ > 2 μm, Q > 0.5, and f₀ ≃ 50 kHz. The effect of acceleration and acoustic noise is negligible for a total acceleration noise of 10 g or less and a total acoustic noise of 74-dB sound pressure level. The power-supply noise depends on the bias conditions of the MEMS element, but is negligible for MEMS switches with a bias voltage of 0 V and a total noise voltage of 0.1 V or less. It is also found that metal-to-metal contact series switches result in much less phase noise than standard capacitive shunt switches. The phase noise increases rapidly for low spring-constant bridges (k = 0.24 N/m), low-height bridges, and bridges with a large mechanical damping (Q < 0.3). Also, varactor-based designs result in 30-40 dB more phase noise than switch-based circuits. This paper proves that microwave passive circuits built using MEMS switches (with a proper mechanical design) can be used in most commercial and military applications without any phase-noise penalty     

A wide range analog MMIC attenuator with integral 180° phaseshifter

A circuit topology is discussed for achieving a wide-range analog attenuator in MMIC form using enhancement mode FET's by combining it with a 90° phase shift network. By switching the phase shift network between a 90° phase lead high-pass structure and a 90° phase lag low-pass structure, a dual-purpose circuit is formed comprising both a variable attenuation and 180° phase shift function. The approach requires only a single control voltage for the attenuator and achieves an attenuation range of over 30 dB in L-band with less than 10° of phase imbalance over the range. In the low-loss state, the phase shifter achieves a 10° phase balance over a 250 MHz bandwidth with less than 0.3 dB of amplitude imbalance