ang Li

Memory polynomial based adaptive predistortion for Radio over Fiber systems

In this paper, a measurement apparatus based Radio-over-Fiber system prototype, including a Vector Signal Generator (VSG), a semiconductor laser, a photodetector and a spectrum analyzer, is build to study the nonlinear effects of the RoF system, which is widely regarded as a promising technique for microcell applications of the future wireless networks. The memory polynomial nonlinear model is utilized to compensate the nonlinearities in the RoF system. A three carrier Wideband Code Division Multiple Access(WCDMA) signal is applied to this test platform. The experimental results illustrate that the predistorter can improve the Adjacent Channel Power Ratio (ACPR) more than 10-dB.

Embedded ARM-based automatic gate bias control system for LDMOS RF power amplifiers

An intelligent gate voltage control system is proposed in accordance with changes of temperature and drain current. The system is implemented in an embedded ARM platform ADuC7026 (ARM7), in which the uC/OS-II operating system is utilized to the control the compensation process for the deterioration of the LDMOS power amplifier (PA) at different temperatures in real-time. With the interrelation of temperature, bias gate voltage and drain current, the parameters of LDMOS PAs could be changed automatically in accordance with external conditions and drain current through real-time monitoring the working status of the power amplifier so as to maintain its linear stability. Finally, the effectiveness and reliability of the system are verified directly by the good performance of the simulation and hardware experiments.

A 460MHz Doherty power amplifier for IMT-Advanced systems

In this work, a Doherty power amplifier is presented for IMT-Advanced system at 450-470MHz frequency band. An imperfect Quarter-wave transmission line, which consisted of two shunt capacitors and a series microstrip line, is adopted to replace the bulky impedance inverter quarter-wave transmission line for designing the Doherty power amplifier (PA). Both the traditional and proposed structures for the Doherty power amplifiers were implemented. Comparing with the traditional Doherty amplifier, the size of the circuit and the manufacturing costs are decreased obviously. The measurement results of the proposed Doherty PA exhibit good performance as well as the traditional Doherty power amplifier. For a input signal with a 7.8dB Peak to Average Power Ratio (PAPR), the measured drain efficiency of the proposed Doherty power amplifier is 48.5% at an average output power of 43.0 dBm, which is a 7.8dB backed - off the peak output power. Moreover, in order to improve the linearity of the proposed Doherty power amplifier, the augmented Hammerstein and polynomial predistorter are used to linearize the proposed Doherty power amplifier. After digital predistortion, the adjacent channel leakage ratio (ACLR) reaches -45.5dBc at an average output power of 43.0 dBm, which can satisfy the requirements of the IMT-Advanced systems.

Bias circuit design of RF power amplifiers for TDD systems

In Time Division Duplex(TDD) system, the radio frequency (RF) power amplifier in a repeater is turned on only when it receives RF signal, thus implementing the sub-frame synchronization and the second conversion point of timeslots is important in TDD system. This paper introduce a bias circuit design to realize the control of the RF power amplifier in the down-link through envelop detection of the received RF signal. The experimental results demonstrated that the proposed bias circuit can properly control the operation status of the power amplifier for a TD-SCDMA system.

Electronically Tunable Impedance-Matching Networks for Intelligent RF Power Amplifiers in Cognitive Radio Systems

This paper presents the simulation and optimization design of the electronically tunable impedance matching networks for intelligent RF power amplifiers in a cognitive radio system. Reconfigurable elements, such as varactors and RF switches are utilized to achieve the dynamic impedance matching both in the input and output matching circuit, providing coarse and fine tuning of the target impedances with low loss and excellent impedance coverage from 500MHz to 800MHz. The topology of varactor model is illustrated to ensure the precision of simulation. In addition, high-precision bias voltage controlling system is designed to improve the nonlinear problem caused by the varactor. The simulation results demonstrate the excellent performance of the tunable networks, satisfying the requirement of the cognitive radio systems.

A Novel Load Network Using Imperfect Quarter-Wave Transmission Line for Three-Stage Doherty Power Amplifiers

In this work, a 460MHz three-stage Doherty power amplifier is designed for the International Mobile Telecommunications-Advanced system at 450-470MHz frequency band by using imperfect quarter-wave transmission line, which consists of two shunt capacitors and a series micro strip line to replace the bulky impedance inverter quarter-wave transmission line load network in the structure of the three-stage Doherty power amplifier. Taking 1-tone signal as input signal, the simulation results illustrate that high power added efficiency of 52% is achieved at an average output power 43.8dBm which is 9.5dB back off the peaking power. Compared with the typical three-stage Doherty power amplifier, the circuit size of the novel load network is shirked obviously. Moreover, high efficiency of the designed three stage power amplifier is also achieved at an average output power largely baked off the peaking output power by utilizing the novel load network.