非迭代查找表预失真新方法

提出一种新的非迭代查找表预失真方法,该方法采用改进型的查找表预失真器,根据输入的同相和正交(IQ)信号及查找表的值,经过乘加运算后就可直接得到预失真处理后的IQ两路输出,避免了坐标转换所带来的附加计算,使预失真器的结构更简单,计算量更低,并结合单路反馈技术,降低了预失真系统硬件成本。仿真结果证明:该方法是正确的,能很好的抑制带内和带外失真,达到了比较好的预失真线性化效果。     

查找表联合记忆效应补偿技术的宽带自适应预失真算法

为了能够对记忆型功率放大器线性化处理,并能一定程度克服其记忆效应,该文介绍一种自适应数字预失真器。该数字预失真器采用查找表与记忆效应补偿技术相结合的方法,并且利用内插值方法有效减小了查找表幅度量化过程产生的误差。相比记忆多项式预失真器,这种预失真器的计算复杂度较小,却能够得到与其相近的线性化效果。基于功率放大器记忆多项式模型,利用OFDM(Orthogonal Frequency Division Multiplexing)宽带信号验证该文提出的预失真器对记忆型非线性功率放大器的良好线性化效果。     

基于循环平稳特性的欠采样宽带数字预失真研究

为了解决行波管(TWT)宽带数字预失真(DPD)中反馈回路ADC采样率过高的问题，该文利用信号的循环平稳特性证实可通过欠采样下的输出信号估计功放的非线性模型参数，然后由功放非线性模型参数和输入信号可恢复出与高采样率下效果相似的功放输出信号，最后通过传统的间接学习结构对功放进行数字预失真以实现行波管的线性化。为了验证该方法，利用20 MHz LTE信号驱动一只55 W的X波段行波管放大器(TWTA)。数字预失真反馈回路的ADC采样率从61.44 Msps降低至6.144 Msps和3.072 Msps，但线性化效果变化不大，表明欠采样方法是有效的。     

基于改进型径向基函数神经网络的功放线性化

提出了一种基于改进型径向基函数神经网络(MRBFNN)的数字预失真线性化模型,用于更为精确地矫正宽带射频功率放大器的动态非线性。该神经网络模型的输入层使用传统的延时抽头以补偿功放的线性记忆效应,同时对每个抽头进行级数展开用于补偿功放的非线性记忆效应,从而更好地抑制功放的动态非线性失真。文中使用WCDMA 三载波信号对一个460MHz 的Doherty 功率放大器进行数字预失真线性化实验。实验结果表明,与传统数字预失真线性化模型相比,基于改进型径向基神经网络的数字预失真线性化模型能更好地抑制宽带功放动态非线性引起的带外频谱再生,其三阶互调(IMD3)失真最多可以抑制23dB,大大提高了功放的线性度,验证了所提出的数字预失真线性化模型的有效性。     

一种基于非均匀记忆多项式的数字预失真方法

为了提高功率放大器线性化性能，提出了一种基于非均匀记忆多项式(Nonuniform Memory Polynomial, NMP)和线性插值查找表(Look-Up Table, LUT)结合的基带数字预失真方法。与传统的记忆多项式(Memory Polynomial, MP)模型相比，NMP模型具有更少的系数和较低的计算复杂度，同时能获得相近的建模精度。在NMP模型的基础上，采用线性插值LUT代替求解多项式的计算过程，进一步降低预失真处理的计算复杂度。对提出的数字预失真方法进行了仿真测试，仿真结果表明，相比基于传统MP模型的预失真方法，提出的方法能够获得相近的线性化性能，并在预失真处理消耗时间上有较大优势。     

用GaAs MMIC实现2.1GHz的预失真线性化单片

介绍了一种预失真线性化单片电路,该电路单电源工作,采用预失真技术结合有源反馈的方法,完成了单片预失真线性化电路的研制.预失真线性化单片电路采用75mm GaAs MMIC工艺研制,芯片面积约为4mm2.结果表明,2.1GHz时此预失真单片电路可改善放大器的三阶互调分量9dB.     

功率放大器及预失真器模型的设计

传统多项式常用在功率放大器模型和预失真器模型的设计里。然而,随着多项式阶数逐次增加时,传统多项式模型表现出数据的不稳定性。详细介绍了一种用于功率放大器以及预失真器模型的正交多项式。从理论上讲,传统多项式与正交多项式模型是等效的,但实践表明,在有限精度范围内,这两种方法对数据进行了不同的处理。MATLAB仿真结果表明,正交多项式可以减轻数值不稳定的问题,建立高精度的功率放大器和预失真器模型,进而改善系统的线性化指标。     

用GaAs MMIC实现2.1GHz的预失真线性化单片

介绍了一种预失真线性化单片电路,该电路单电源工作,采用预失真技术结合有源反馈的方法,完成了单片预失真线性化电路的研制.预失真线性化单片电路采用75 m m Ga As MMIC工艺研制,芯片面积约为4 mm2 .结果表明,2 .1GHz时此预失真单片电路可改善放大器的三阶互调分量9d B     

一种基带预失真RF功率放大器线性化技术的模型仿真与实验

提出了一种基于相关函数计算的自适应环延迟补偿法,用于功率放大器的的数字式基带预失真线性化技术。对采用这种软件延时补偿方法的预失真系统特性进行了仿真,并采用通用的数字信号处理器在硬件上实现了一个功放预失真系统性化模型进行了仿真,并采用通用的数字信号处理器在硬件上实现了一个功放预失真线性化模型。仿真和实验结果表明,在功率放大器的基带预失真中采用方法可以获得至少２０ｄＢ的线性度改善。     

基于数/模混合预失真技术的功放线性化北大核心CSCD

随着移动通信信号带宽的增加,传统功率放大器数字预失真线性化技术越来越受到采样率的限制。为了使线性化效果更好,文中提出了一种数字预失真和模拟预失真相结合的混合预失真器,利用模拟预失真宽带宽的特点和数字预失真线性化能力强的优势,把模拟预失真和数字预失真融合在一起,共同补偿功放的非线性。由于受实验设备采样率的限制,文中采用了带宽为60 MHz的5 G NR信号对一个中心频率为3.5 GHz的射频功放进行实验验证。实验结果表明:提出的混合预失真器不仅优于单独的数字预失真器和模拟预失真器的非线性矫正性能,而且还能改善数字预失真因采样率限制无法改善的带外互调失真。     

基于超前-滞后校正的微机械陀螺正交误差补偿

提出了一种基于超前-滞后校正的微机械陀螺正交误差补偿方法。根据振动式陀螺仪的驱动模态和检测模态运动特征,推导了包含正交误差的陀螺系统动力学方程,提出了一种正交误差闭环反馈回路。运用超前-滞后校正,设计了闭环控制环节,将正交误差输出补偿到陀螺表头传感元件；同时,在陀螺仪接口电路部分,设计了由正交输出量控制的VGA模块,进一步补偿正交误差。结果表明,提出的超前-滞后闭环补偿回路相比于PID控制器,响应速度更快,稳定性更好,陀螺的正交稳态误差从23.5 mV减小到0.41 mV,误差补偿效果明显,有效提高了陀螺的测量精度。     

Nonlinear feedback control of chaos in permanent magnet synchronous motor

Permanent magnet synchronous motor (PMSM) will demonstrate chaotic phenomena when its parameters fall into a certain area. The performance of PMSM will degrade because of chaos. Therefore, chaos should be suppressed or eliminated. According to the features of this practical plant, the drawbacks of existing control methods are analyzed, and the nonlinear feedback control method is suggested to control the chaos in PMSM. The nonlinear feedback principle is developed using the direct axis and the quadrature axis stator voltage as manipulated variables. The control target will become a unique asymptotically stable equilibrium under the nonlinear feedback principle, by this way, the controlled states can reach the target and the control objective can be implemented. This method can be physically realized using nonlinear state feedback. The control forces can be put into effect at any time. The target of the method may be any point in the strange attractor. The influence of the model error and the measurement noise upon the control performance is studied via simulations. Simulation results show the effectiveness of this method under the presence of the model error and the measurement noise.     

直接正交上变频调制器的镜频抑制与本振泄漏对消技术研究

镜频干扰和本振泄漏是制约直接正交变频技术在无线通信收发信机中应用的主要技术瓶颈之一.通过分析直接正交上变频调制器中引起镜频干扰和本振泄漏的原因,利用逆向校正方法,给出了一种闭环反馈式正交基带信号预失真数字幅相平衡补偿电路,提出了一种通过调节基带信号的直流偏置实现本振泄漏对消的措施,提高了直接正交上变频器的镜频抑制和本振泄漏对消能力,并给出了在小型化CDMA发射机中的应用实例.     

Digital predistortion based on single-feedback method and indirect learning structure

This paper proposes a novel digital predistortion method for both memory and memoryless power amplifiers, which only needs one feedback circuit. In comparison with the previous methods, the proposed method has the greatest advantage that it can eliminate the gain and phase imbalance errors of the quadrature demodulator without digital IQ compensator, and the performance of digital predistortion can be improved with lower costs and less computation complexity. Combining with the indirect learning structure, it is easy to design the predistorter. Experimental results show the correctness and effectiveness of the proposed method.     

A systematic realization of third-order quadrature oscillator with controllable amplitude

A systematic realization of third-order quadrature oscillator using a voltage-mode non-inverting lowpass filter and a voltage-mode inverting lossless feedback integrator is presented in this paper. The proposed circuit consists of two multiple-output differential voltage current conveyor transconductance amplifiers (MO-DVCCTAs), two grounded resistors and three grounded capacitors. The new circuit provides three quadrature voltage outputs, two high-impedance quadrature current outputs, and one high-impedance current output with controllable amplitude, simultaneously. When the input bias current of the first MO-DVCCTA is a modulating signal, the circuit can generate amplitude modulation or amplitude shift keying signals. The condition of oscillation and the frequency of oscillation can be controlled independently through grounded resistors. The proposed circuit only uses grounded capacitors and grounded resistors, which can be easily implemented as an integrated circuit. The experimental results and H-Spice simulation results are given to confirm the theoretical analysis.     

递归SOQPSK-TG信号的两状态判决反馈解调算法

针对利用两状态网格图对递归部分响应成形偏移正交相移键控SOQPSK-TG信号进行解调时,网格图状态变量与累积相位不存在一一对应关系的问题,研究了解决此问题的判决反馈解调算法。该算法根据两状态网格图,在网格状态转移过程中,通过判决反馈,得到状态变量对应的累积相位。仿真结果表明,在信噪比大于0 dB时,SOQPSK-TG信号两状态判决反馈解调算法可以获得接近四状态解调的误比特性能。     

Design and implementation of quadrature bandpass sigma-delta modulator used in low-IF RF receiver

This paper presents the design and implementation of quadrature bandpass sigma-delta modulator.A pole movement method for transforming real sigma-delta modulator to a quadrature one is proposed by detailed study of the relationship of noise-shaping center frequency and integrator pole position in sigma-delta modulator.The proposed modulator uses sampling capacitor sharing switched capacitor integrator,and achieves a very small feedback coefficient by a series capacitor network,and those two techniques can dramatically reduce capacitor area.Quantizer output-dependent dummy capacitor load for reference voltage buffer can compensate signal-dependent noise that is caused by load variation.This paper designs a quadrature bandpass Sigma-Delta modulator for 2.4 GHz low IF receivers that achieve 69 dB SNDR at 1 MHz BW and-1 MHz IF with 48 MHz clock.The chip is fabricated with SMIC 0.18 μm CMOS technology,it achieves a total power current of 2.1 mA,and the chip area is 0.48 mm2.     

Feedback method for suppressing carrier leak

A feedback method for suppressing carrier leak (and any carrier-frequency output component due to a d.c. offset at the input) in balanced modulators and multipliers is described which promises to be particularly effective when used in quadrature modulation systems. The method is basically simple, but a search of the literature has failed to uncover any reference to a similar scheme.     

SNR Estimation in OFDM System by the Correlation of Decision Feedback Signal

In the channel-varying environment, it is very important to estimate the signal to noise ratio (SNR) of received signal and to transmit the signal effectively for the modern communication system. The performance of existing non-data-aided SNR estimation methods are substantially degraded for high level modulation scheme such as M-ary amplitude and phase shift keying or quadrature amplitude modulation. In this paper, we propose a SNR estimation method which uses zero point auto-correlation of received signal per block and auto/cross-correlation of decision feedback signal in orthogonal frequency division multiplexing (OFDM) system. Proposed method can be studied into two types; Type 1 can estimate SNR by zero point auto-correlation of decision feedback signal based on the second moment property. Type 2 uses both zero point auto-correlation and cross-correlation based on the fourth moment property. In block-by-block reception of OFDM system, these two SNR estimation methods can be possible for the practical implementation due to correlation based the estimation method and they show more stable estimation performance than the previous SNR estimation methods. Also, we mathematically derive the SNR estimation expression according to computational difference of auto/cross-correlation. Finally, Monte Carlo simulations are used to verify the proposed method.     

Carrier Synchronization and Detection of QASK Signal Sets

A carrier regeneration loop which generates highly coherent quadrature reference signals for quadrature amplitude-shift keying (QASK) demodulation is presented. The loop employs the principle of decision feedback and has a structure analogous to a decision feedback loop for quadriphase signals suggested earlier in the literature. The error probabihty performance of QASK is computed in the presence of the noisy carrier reference signals provided by the above loop. It is demonstrated that when the ratio of data rate to loop bandwidth is 50 or greater, then for all practical purposes, ideal QASK error probability performance is achieved.