LNA linearization solution for direct conversion receiver using under-sampling technique in reference receiver

The paper proposes a method for linearizing low noise amplifiers (LNAs) in multichannel direct conversion receivers. The proposed direct conversion receiver (DCR) uses a linear reference receiver to extract distortion information, which is then fed to an adaptive circuit for linearizing the main channel signal. The proposed DCR differs from prior LNA linearization techniques in that the reference channel in the proposed DCR uses analog to digital converter (ADC) with an undersampling technique to extract reference information. The low-speed ADC also serves as a downconverter, shifting radio frequency (RF) signal to baseband and allowing for all further linearization processing to be performed digitally at a low-sampling data rate. This significantly reduces cost, design complexity, and energy consumption. The effectiveness of the proposed design is theoretically verified through MATLAB simulation and practically measured for a 65 Mhz band of ultra-high frequency (UHF) DCR capable of simultaneously receiving four 16–QAM channels of the same bandwidth of 4 Mhz. The MATLAB software simulation results show that the proposed approach significantly improved the signal-to-noise and distortion ratio (SNDR) for the channel of interest by approximately 30 dB in the worst distorted channel. For hardware implementation, the distorted signals are sampled from a commercial LNA (ZFL–500LN+) by a customized FPGA board. Results from measurements show an improvement of 14.6% for error vector magnitude (EVM) in a strong distortion scenario of 16–QAM modulation signal.     

交调失真影响下星间微波光子链路接收灵敏度优化

高输入信号功率时的交调失真是降低星间微波光子链路接收灵敏度的主要因素。考虑输入N路四相相移键控(QPSK)调制信号的情形,建立了强度调制/直接检测(IM/DD)星间微波光子链路模型。利用傅里叶级数展开、傅里叶变换/逆傅里叶变换和Graf加法定理,推导出了接收信号任意谐波和交调分量的解析表达式,在确定三阶交调失真个数的基础上,得到了接收光功率与信号噪声失真比(SNDR)之间的关系。着重分析了不同调制方式下链路接收灵敏度与信道数和调制系数之间的关系。当调制系数较小时,接收灵敏度对信道数变化不敏感。随着调制系数的增大,接收灵敏度先增大后减小,存在最佳的调制系数可以使链路接收灵敏度最高。     

面向超短波接收机射频前端的电磁脉冲效应仿真与效应分级方法

针对接收机射频前端在电磁脉冲环境作用下的电磁损伤过程模拟问题,以超短波接收机为具体研究对象,基于超外差式接收机电路功能模型,采用Verilog-a和SPICE网表联合建模方法,建立了射频前端低噪声放大器（LNA）电磁脉冲效应仿真模型(Extended LNA Model),并通过S参数仿真和瞬态仿真验证了LNA电磁脉冲效应模型具备正常功能仿真能力;为验证该模型的电磁脉冲损伤模拟能力,以标准电磁脉冲波形作为激励,以偶极子天线作为简化的天线前门耦合通道,在不同强度电磁脉冲作用下,接收机中频电路信号输出表现出了无影响、干扰、损毁的电磁脉冲效应过程,说明了建模方法的有效性;最后以EMP-天线耦合电压峰值作为阈值指标,分析得到了超短波接收机不同电磁脉冲效应等级对应的电压峰值阈值数据。     

场效应器件低温特性与低噪声放大器

高温超导滤波器与低噪声放大器(LNA)组成的射频接收机前端设备具有高选择性、高灵敏度和极低的噪声,因而展现出广阔的应用前景.本文研究了场效应器件的低温物理特性和电学参数,研制了一种适用于高温超导微波接收系统的低温低噪声放大器,在60K工作温度下,具有很好的噪声特性.包括高电子迁移率场效应晶体管在内的元件参数均在60K温度下进行了实际测量.放大器的各项指标与设计值吻合,工作频段为800MHz～850MHz,增益大于18dB,输入输出驻波比小于1.2,噪声系数小于0.22dB.     

平衡衔铁受话器的非线性特性与失真仿真模型

平衡衔铁受话器(BAR)具有尺寸小、电声转换效率高和灵敏度高等特点。在大振幅振动时, BAR存在显著的非线性,并导致较严重的失真。利用磁路的集总参数模型(LPM)深入研究BAR的非线性,确立可表征其非线性特性的4个非线性参数,采用迭代计算方法研究平衡衔铁磁阻对非线性特性的重要影响。基于所提出的网格移动和旋转等效的有限元模型(FEM),考虑平衡衔铁磁阻的非线性,准确仿真计算得到非线性参数,再将它们代入到非线性LPM模型中,最终建立FEM与LPM相结合的失真仿真模型。实验结果表明,该失真仿真模型可比较准确地预测BAR在不同加载电压时的总谐波失真以及二次和三次谐波失真。     

在低场MRI系统中用数字接收机测量梯度波形的方法

提出了一种用数字接收机来测量低场系统中梯度波形的方法,详细介绍了该数字接收机接收音频信号的原理,并且对接收机的音频接收性能进行了测试. 最后利用该接收机测得的梯度波形,设置了系统的预加重参数,有效地减小了梯度线圈引起的涡流.     

Research on front-end electronics gain compensation of MCP imaging detector北大核心CSCD

基于微通道板电子倍增电荷分割型阳极的成像探测器常用于行星大气、气辉等微弱信号探测。针对探测器读出电路增益不相等导致探测器成像产生畸变的问题,利用理论分析结合MATLAB仿真揭示了不同畸变图像的形成机制,在该基础上提出了一种探测器读出电路增益补偿方法减小探测器成像畸变。通过MATLAB仿真和实验测试结果表明该文提出的方法能够有效减小由于读出电路增益不相等导致的探测器成像畸变。     

345 GHZ PROTOTYPE SIS MIXER WITH INTEGRATED MMIC LNA

We report on heterodyne measurements at submillimeter wavelengths using a receiver with a Superconductor-Insulator-Superconductor (SIS) mixer device and a Microwave Monolithic Integrated Circuit (MMIC) cryogenic low noise amplifier (LNA) module integrated into the same block. The mixer characterization presented in this work demonstrates the feasibility of operating a MMIC LNA in close proximity to the SIS device without penalty in mixer performance due to heating effects. Verification of this functionality is crucial for the ongoing development of SuperCam, a 64-pixel focal plane array receiver consisting of eight, 1 × 8 integrated mixer/LNA modules. The test setup included a mixer block modified to accept a MMIC amplifier. Our tests show that the LNA can be operated over a broad range of V_drain voltages from 0.40–1.40 V, corresponding to dissipative powers of 2.6–29 mW. We observe no significant effect on the measured uncorrected receiver noise temperatures in the 345 GHz band.     

Optimization of broadband RF performance and ESD robustness by π-model distributed ESD protection scheme

Large electrostatic discharge (ESD) protection devices close to the I/O pins, beneficial for ESD protection, have an adverse effect on the performance of broadband radio-frequency (RF) circuits for impedance mismatch and bandwidth degradation. A new proposed ESD protection structure, $\pi$-model distributed ESD ($\pi$-DESD) protection circuit, composed of one pair of ESD devices near the I/O pin, the other pair close to the core circuit, and a coplanar waveguide with under-grounded shield (CPWG) connecting these two pairs, can successfully achieve both excellent ESD robustness and good broadband RF performance. Cooperating with the active power-rail ESD clamp circuit, the experimental chip in a 0.25-μm CMOS process can sustain the human-body-model (HBM) ESD stress of 8 kV.     

一种可在线更新的PET实时查找表电路的设计与实现

介绍了一种正电子发射断层成像术实时查找表电路。该电路接收符合电路输出的位置信号和能量信号,用查表的方法完成重心法中的除法运算,然后再第二次查表得到该γ光子所入射到的晶格的离散化坐标值和能量阈值,并完成能量甄别以剔除部分散射事件。此外,该电路还结合了呼吸门控和心电门控功能。查找表存储在flash器件中,由CPLD控制读写。本设计的特点是利用硬件电路来完成查找表功能,效率更高,每次事件的查表寻址的延迟时间小于100ns,并且可以在线更新查找表的内容,使用方便。另外,还说明了用CPLD来读写NORflash的方法,以及该电路与系统中其它模块间的数据通信方法。     

Design and implementation of the CAPS receiver

In this paper, based on analyses of the Chinese Area Positioning System (CAPS) satellite (GEO satellite) resources and signal properties, the signal power at the port of the receiver antenna is estimated, and the implementation projects are presented for a switching band C to band L CAPS C/A code receiver integrated with GPS receiver suite and for a CAPS dual frequency P code receiver. A microstrip receiving antenna is designed with high sensitivity and wide beam orientation, the RF front end of the C/A code and P code receivers, and a processor is designed for the navigation baseband. A single frequency CAPS C/A code receiver and a CAPS dual frequency P code receiver are built at the same time. A software process flow is provided, and research on relatively key techniques is also conducted, such as signal searching, code loop and carrier loop algorithms, a height assistant algorithm, a dual frequency difference speed measurement technique, a speed measurement technique using a single frequency source with frequency assistance, and a CAPS time correcting algorithm, according to the design frame of the receiver hardware. Research results show that the static plane positioning accuracy of the CAPS C/A code receiver is 20.5–24.6 m, height accuracy is 1.2–12.8 m, speed measurement accuracy is 0.13–0.3 m/s, dynamic plane positioning accuracy is 24.4 m, height accuracy is 3.0 m, and speed measurement accuracy is 0.24 m/s. In the case of C/A code, the timing accuracy is 200 ns, and it is also shown that the positioning accuracy of the CAPS precise code receiver (1 σ) is 5 m from south to north, and 0.8 m from east to west. Finally, research on positioning accuracy is also conducted. Supported by the Knowledge Innovation Program of Major Projects, Chinese Academy of Sciences (Grant No. KGCX1-21) and the National High Technology Research and Development Program of China (Grant No. 2004AA105030)     

Computer Aided Analysis of Nonlinear Distortion for Laser Diode under Intensity Modulation

1.IntroductionNonlineardistortionisanimportantindextoappreciateasubcarriermultiplexing(SCs)lightwavetransmissionsystem.Itconsistsofthedistortionoflaserdiode(LD)module,distortionoffiber--optictransmissionsystemandthatofreceiversystem,amongwhichLD'shasagreatinfluenceonsystem'scharacteristicsbecauseitisanonlineardeviceinitself.LDnonlineardistortioncomesfromP--Icharacreristicsandinteractionbetweenphotonsandelectrons.WhenLDworksatlineararea,theformercanbeneglectedandthelatteristhemain,whichisd…     

Nonlinear sigma model method for the J1-J2 Heisenberg model: disordered ground state with plaquette symmetry

A novel nonlinear sigma model method is proposed for the two-dimensional J1-J2 model, which is extended to include plaquette-type distortion. The nonlinear sigma model is properly derived without spoiling the original spin degrees of freedom. The method shows that a single disordered phase continuously extends from a frustrated uniform regime to an unfrustrated distorted regime. By the continuity and Oshikawa's commensurability condition, the disordered ground states for the uniform J1-J2 model are plaquette states with fourfold degeneracy.     

Nonlinear Frequency-Modulation Distortion Analysis for VCO Based on Harmonic Balance Method

The analysis methods for the steady-state responses of the voltage tuning negative resistance oscillator (voltage-controlling oscillator, VCO) by the microwave nonlinear autonomous circuit harmonic balance method in millimeter-wave bands are studied in the paper. Firstly, the quasi-periodic characteristic of the steady-state response of the VCO modulated by a periodic signal is proved. Then, on the bases of the harmonic balance analysis and the inter-modulation balance analysis, a novel method for obtaining the steady-state tuning performance and the nonlinear frequency-modulation distortion characteristic of the VCO is presented. The total analysis process is aimed to a kind of NRD-guide Gunn diode VCO. The large-signal lumped equivalent circuit model of the millimeter-wave P⁺N-junction varactor is also given for explaining the algorithm and the principle of the NRD-guide VCO.     

An Inverter-Based,CMOS, Low-Power Optical Receiver Front-End

In this paper, a low-power optical receiver front-end which consists of a transimpedance amplifier (TIA) and three stages of limiting amplifier (LA) for 2.5 Gb/s applications is proposed in 0.18 µm CMOS technology. The proposed TIA benefits from a modified inverter structure, in which the input resistance is properly reduced due to the use of diode-connected transistors in comparison with conventional inverter circuit. Also, an active inductor is used in parallel with a diode-connected transistor at the output node, which provides a low output resistance, while it resonates with the load capacitance to extend the ?3 dB frequency bandwidth. Moreover, three stages of LAs are used to obtain extra gain, in which each LA cell uses active inductor load. However, HSPICE simulations for the proposed TIA circuit show a 42.24 dBΩ transimpedance gain, 1.96 GHz frequency bandwidth, 11.7 pA/√Hz input referred noise, and only 972 µW of power consumption at 1.5 V supply. Also, simulation results for the whole receiver system show a 75.6 dB gain, 1.7 GHz frequency bandwidth, and 6.54 mW of power consumption at 1.5 V supply. Finally, simulation results indicate that the proposed receiver system has good performances to be used as a low-power optical receiver front-end.     

A Signal processing method of OFDM communication receiver based on CNN

Orthogonal frequency division multiplexing (OFDM) the signal processing is a key issue in wireless communication research. The multipath effect and Doppler shift of wireless communication channels can lead to distortion of the transmitted signal, which poses a considerable challenge to the information recovery of communication receivers. This paper presents the signal processing method of OFDM communication based on convolutional neural network (CNN). The method replaces all signal processing modules of the OFDM communication receiver with CNN, and the information is recovered by the CNN. In order to adapt to the processing of communication signals, we designed a one-dimensional convolutional neural network (1D-CONV-CNN) model as the neural network structures by this method. Simulation results indicate that the signal processing method effectively reduces the bit error rate (BER) and improves its performance compared with the conventional reception method under different channel conditions.     

基于机器学习和可见光光谱的冬小麦叶片氮积累量估算

在拔节期分4次采集了6个施氮水平下的冬小麦冠层图像,同步进行取样并以凯氏定氮法测定叶片含氮量,进而计算叶片氮积累量。利用随机森林算法分割冠层图像之后提取冠层覆盖度、可见光波段(R, G和B)三个分量及其衍生的5个色彩指数。以冠层覆盖度外加色彩指数、色彩分量的两种非线性回归,以及人工神经网络、支持向量回归、随机森林3种机器学习算法建立了冬小麦叶片氮积累量的估算模型。结果表明利用色彩指数的非线性回归模型的估算精度稍低于其他方法,而随机森林算法的拟合精度最高,但存在明显的过拟合现象。其他三种方法,即以冠层覆盖度及色彩分量为输入变量的非线性回归、支持向量回归和人工神经网络方法,均具有较高的拟合精度和泛化性能。     

Nonlinear dynamic range compression deconvolution

We introduce a dynamic range image compression technique for nonlinear deconvolution; the impulse response of the distortion function and the noisy distorted image are jointly transformed to pump a clean reference beam in a two-beam coupling arrangement. The Fourier transform of the pumped reference beam contains the deconvolved image and its conjugate. In contrast to standard deconvolution approaches, for which noise can be a limiting factor in the performance, this approach allows the retrieval of distorted signals embedded in a very high-noise environment.     

磁共振现代射频脉冲理论在非均匀场成像中的应用

在磁共振非均匀场成像中，传统的射频脉冲导致回波信号的衰减.为了减小和消除这种磁共振信号的衰减，在讨论了经典理论的基础上根据非线性动力学中的逆散射理论和Shinnar-Le Roux方法导出了用于非均匀场成像的射频脉冲设计方法.模拟结果表明，采用逆散射理论和Shinnar-Le Roux方法优化的脉冲序列可以明显提高信号的信噪比. 关键词： 磁共振成像 射频脉冲 非线性系统