Xu Changzhi

Bio: Xu Changzhi is an academic researcher from China Academy of Space Technology. The author has contributed to research in topics: Signal & Optical communication. The author has an hindex of 1, co-authored 4 publications receiving 5 citations.

A Generalized High-Efficiency Broadband Class-E/F3 Power Amplifier Based on Design Space Expanding of Load Network

Abstract: This article presents an analytical and coherent design method for the generalized high-efficiency broadband parallel-circuit (PC) Class-E/F 3 power amplifier (PA). By importing the initial phase shift of the third harmonic and adding series reactive element to the load network, a free design parameter can be defined and the design space of the load network parameters are expanded. The design equations of the idealized waveforms and the optimum values of the load network components are derived in detail, and the performance of the peak drain voltage, maximum operating frequency, and power output capability can be improved. In addition, with the expanding space of load network, the generalized PC Class-E/F 3 structure exhibits broadband capability. A matching method with the real frequency technique (RFT) and the de-embedding technique is presented to design the optimal broadband matching network. To verify the validity of the proposed method, a broadband high-efficiency PA working from 1.7 to 2.6 GHz (fractional bandwidth of 42%) is designed. The experimental results of the fabricated PA present high-efficiency characteristics of 68.5%-81% drain efficiency and 62%-75.8% power-added efficiency with 38.8-40.5 dBm output power over the whole operation bandwidth.

Complex-Valued Pipelined Chebyshev Functional Link Recurrent Neural Network for Joint Compensation of Wideband Transmitter Distortions and Impairments

Abstract: In this article, a novel digital predistortion (DPD) model based on complex-valued pipelined Chebyshev functional link recurrent neural network (CPCFLRNN) for joint compensation of wideband transmitter distortions and impairments is proposed. The functional link neural network (FLNN) model has attracted much attention from scholars, and many improved models using this structure, such as Chebyshev FLNN, have been applied in the DPD of power amplifiers (PAs). However, these existing neural network models cannot deal with complex-valued input signals simultaneously, and the real-valued model structure will introduce cumbersome training algorithm and result in a long training time. The pipelined recurrent neural network (PRNN) has been successfully applied to nonlinear signal prediction because of its excellent ability for dealing with nonlinear nonstationary signals. Therefore, the PRNN model containing Chebyshev structure is extended to complex domain for the first time to obtain the CPCFLRNN model for DPD application. Considering the strong correlation of in-phase and quadrature phase (I/Q) components of the transmitter signal, the real time recurrent learning (RTRL) algorithm based on fully complex activation function is selected and extended to complex domain to obtain the complex-valued RTRL (CRTRL) algorithm for CPCFLRNN model training. A GaN PA was employed to verify the effectiveness of the proposed models. And the input signal is a 30MHz LTE signals which consists of I/Q imbalance and dc offsets. The experimental results show that the proposed CPCFLRNN model have more accurate modeling effect and better linearization performance compared with the conventional DPD models.

Detection Method of Focal Plane Arrays With Noise Suppression for Optical Communications

Abstract: In many optical communication systems, in order to make the optical networking convenient and meet the application requirements, the optical terminals need to work in the same band and at the extremely closely adjacent working wavelengths. In practice, because of the light reflection and scattering of the wireless channels with the suspended particles, parts of the emitted optical signals will be reflected to the focal plane array (FPA). On the other hand, because the bandwidth of practical optical filters cannot be made narrow enough, or the sensitivity of FPAs is usually very high, the isolation between the transmitting and receiving optical paths in the terminal cannot be made high enough even if the optical filtering is used. Both the received optical signal from the remote terminal and the transmitted optical signal reflected by the terminal or wireless channels will be detected by the FPA at the same time. The reflected optical signal will interfere with the detection of the received optical signals from the far end, which seriously reduces the detection performance and the accuracy of the light spot centroid calculation. This paper proposes an integral control and increase-decrease counting statistical method for FPAs to eliminate the influence of the reflected optical signal on the signal detection and the noise mean value in the mean value of the total detection signal. The detection sensitivity of the received signal from the remote terminal, the isolation of the transmitting and receiving paths and the accuracy of the light spot centroid calculation are improved by this method. The Cramer-Rao lower bound is calculated and analyzed. In addition, the integral control and increase-decrease counting statistical algorithm is verified by the two software co-simulation, and the simulation results are given to illustrate the feasibility and performance of this method.

Broadband High-Efficiency Quasi-Class-J Power Amplifier Based on Nonlinear Output Capacitance Effect

Abstract: In this brief, a broadband high-efficiency quasi-Class-J power amplifier (PA) based on nonlinear output capacitance effect is proposed. With the influence of the voltage across between drain and source ( $\text{v}_{\mathrm{ DS}}$ ) at the over-driven condition, the negative second harmonic termination has been generated by the nonlinear output capacitance ( $\text{C}_{\mathrm{ out}}$ ). Since the proposed PA is driven into saturation, the current magnitude can be increased which improves the output power and efficiency. Meanwhile, the fundamental termination is modulated near the real axis of the Smith chart by the second harmonic termination, which reduces the ${Q}$ -factor to extend the bandwidth. It is possible to achieve the saturated PA working in the wide frequency band. Finally, the proposed PA shows a relatively high performance of greater than 39.6 dBm saturated output power, and delivers an average of 64 % drain efficiency (DE) from 3.5 to 5.5 GHz.

Broadband High-Efficiency Quasi-Class-J Power Amplifier Based on Nonlinear Output Capacitance Effect

Abstract: In this brief, a broadband high-efficiency quasi-Class-J power amplifier (PA) based on nonlinear output capacitance effect is proposed. With the influence of the voltage across between drain and source ( $\text{v}_{\mathrm{ DS}}$ ) at the over-driven condition, the negative second harmonic termination has been generated by the nonlinear output capacitance ( $\text{C}_{\mathrm{ out}}$ ). Since the proposed PA is driven into saturation, the current magnitude can be increased which improves the output power and efficiency. Meanwhile, the fundamental termination is modulated near the real axis of the Smith chart by the second harmonic termination, which reduces the ${Q}$ -factor to extend the bandwidth. It is possible to achieve the saturated PA working in the wide frequency band. Finally, the proposed PA shows a relatively high performance of greater than 39.6 dBm saturated output power, and delivers an average of 64 % drain efficiency (DE) from 3.5 to 5.5 GHz.

Heuristic Algorithm-Based Design Method for Class-E Switching Circuits

Abstract: In this work, a novel numerical design strategy is presented for designing the class-E switching converters based on the heuristic algorithm. Compared with previous works, the heuristic algorithm requires no initial-value estimations and partial-difference derivations. Therefore, only circuit equations and evaluation functions are necessary for the proposed design method, which is independent of the design parameter number. In this research, a design of a 25 W, 13.56 MHz load-independent wireless power transfer (WPT) system is shown as an example. By defining the evaluation functions considering output-voltage tolerances against the load variations and the power-delivery efficiency, the designed WPT system has a function of loadindependent characteristics. Namely, output load regulations and zero-voltage switching (ZVS) achievements can be achieved at any load resistance. It was confirmed that the prototype implemented system achieved the complete load-independent functions, which proved the effectiveness of the proposed design method.

Comprehensive and Simplified Numerical Design Procedure for Class-E Switching Circuits

Abstract: This paper proposes comprehensive and simplified numerical design procedures for the class-E switching circuits with the Particle Swarm Optimization (PSO) algorithm. The PSO algorithm does not require approximate solutions and partial differentiation derivations. Therefore, the proposed design method has higher convergence stability than Newton’s method-based design. It is also a feature that the PSO algorithm allows the mismatch between the design condition and the design parameter numbers. As a design example, we successfully draw the multiple design curves of the class-E amplifier and frequency multipliers by one-time optimization execution with the modified PSO algorithm. Besides, we show a pretty simple design procedure of the class-E amplifier, which uses only one evaluation function for determining three design parameters. The design accuracy of the proposed design method does not deteriorate compared with the previous design method. We carried out circuit experiments, which achieved power-conversion efficiency of 94.0%. The circuit experiment showed agreement with numerical predictions, which confirmed the validity and usefulness of the proposed design method.

Novel Design Space of Broadband High-Efficiency Parallel-Circuit Class-EF Power Amplifiers

Abstract: This article proposes a broadband high-efficiency parallel-circuit (PC) class-EF power amplifier (PA) along with a quarter-wavelength stub for the first time. By adding a reactive element ${X}$ , the design space is expanded so that the impedance terminations of the fundamental and harmonics are no longer fixed points. Based on the broadband capability of the proposed structure, using a GaN HEMT transistor, a proof-of-concept circuit implemented with the Chebyshev impedance transformation network is designed and fabricated. Experimental results demonstrate a high-efficiency broadband PA operating from 2.6-3.9 GHz, with the average efficiency of 71.5%, the measured output power ( ${P}_{\textit {out}}$ ) of 38.8-40.9 dBm and the power gain of 8.5-10.6 dB.