Linear Amplification Using Nonlinear Components Research Articles

Bandwidth Limitation for the Constant Envelope Components of an OFDM Signal in a LINC Architecture

The linear amplification using non-linear components (LINC) power amplifier architecture uses saturated amplifiers to achieve high efficiency and linearity. However, the non-linear operations for LINC separation lead to bandwidth expansion. The expanded bandwidth causes problems for the analog circuitry and effectively places a limit on the modulation bandwidth of the transmitted signal. We show that for multi-carrier signals, it is the phase component of the transmitted modulation that dominates the spectrum of the LINC components. A novel bandwidth reduction scheme is then proposed for these components. The scheme repetitively limits the bandwidth of the LINC components while inhibiting envelope variations. Measurements show a 46% bandwidth reduction while still meeting the WLAN spectrum mask. This implies an increase of 85% in the modulation bandwidth of the transmitted signal.

Analysis of RF power amplifiers in LINC systems

LInear amplification using Non-linear Components (LINC) is an architecture that achieves linear power amplification for radio-frequency (RF) transmitters. This paper describes the impact of RF power amplifiers (PAs) class on the overall system performances. The linearity and efficiency of the LINC transmitter with different PA classes (AB, B, C, D, E, F, F−1, and J) are evaluated and compared, in terms of error vector magnitude (EVM), adjacent channel leakage ratio (ACLR), and power added efficiency (PAE), for a 16QAM modulation having 5.6 dB peak to average power ratio. Simulations are performed using a gallium-nitride high electron mobility transistor (GaN HEMT) for a power amplifier with an output power of 10 W at 900 MHz.

Design and Experimental Evaluation of a LINC Transmitter for OFDM Systems

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper a digital correction method, which corrects these gain and phase imbalances, is implemented and verified. Commercial analog devices and a digital platform for signal processing purposes are used. The experimental results applied in an OFDM transmitter show a linearity improvement close to 20 dB without reducing the output power and without increasing the in-band distortion.

Power Amplifier and Transmitter Architectures for Software Defined Radio Systems

This paper briefly presents software defined radio (SDR) concept and layouts an overview of the actual state-of-the-art solution for power amplification systems and software enabled transmitters for SDR applications along with emerging related technology trends. Digital predistortion based linearization techniques, as an enabling technology for SDR transmitters, are briefly explained and discussed. Simulation results as well as experimental results are provided for LINC (linear amplification using nonlinear components) delta- sigma based transmitters to illustrate their respective performance and suitability for SDR applications.

Improvement in the Linearity of a LINC Transmitter using Genetic Algorithms

This paper proposes an automatically-adjusted linearization method based on the well-known linearization technique LINC (Linear amplification using Nonlinear Components) applied to the base station transmitter. A correction method of the gain and phase imbalances between both amplifying branches in a LINC transmitter is proposed to reduce the adjacent channel interference. A simple architecture is designed to compensate the unmatching between both branches being the adjusting coefficients calculated by means of a genetic algorithm. Several nonidealities are included in the analysis to deal with a realistic model, such as quadrature modulator imbalances, reconstruction filters and quantization error.

A2×1LINC Transceiver for Enhanced Power Transmission in Wireless Systems

A2×1LINC transceiver based on linear amplification using nonlinear components (LINC) architecture for wireless systems applications is proposed. The layout of the new architecture is presented and the simulation results show that the overall power efficiency of this architecture is superior by more than 300% when compared with that of a regular LINC amplifier. Also the adjacent channel power ratio (ACPR) is lowered to−64.2dBc, compared to−26.1dBc for regular LINC, which improves the system immunity against complex gain imbalances between LINC branches.

An Adaptive Digital Method of Imbalances Cancellation in LINC Transmitters

The linear amplification using nonlinear components (LINC) technique is a well-known power amplifier linearization method to reduce adjacent channel interference in a nonconstant envelope modulation system. Its major drawback is the inherent sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method is described which corrects any gain and phase imbalances in LINC transmitters mainly due to the unmatching of the two amplifier paths. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficient to adjust gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator imbalances and loop delay. A computer simulation has been carried out to verify the method functionality.

Nonlinear Distortion Cancellation Using LINC Transmitters in OFDM Systems

The LInear amplification using Nonlinear Components (LINC) technique is a well-known power amplifier linearization method to reduce out-of-band interferences in a nonconstant envelope modulation system, such as Digital Video Broadcasting (DVB) system, which is based on a very sensitive to nonlinear distortions OFDM modulation scheme. The major drawback of LINC transmitters is the inherited sensitivity to gain and phase imbalances between the two amplifier branches. In this paper, a novel full-digital base band method, which corrects any gain and phase imbalances in LINC transmitters mainly due to the un-matching of the two amplifier paths, is described. Amplifiers are characterized by a level-dependent complex gain using a memoryless model. The method uses adaptive signal processing techniques to obtain the optimal complex coefficients to correct gain and phase imbalances. Its main advantage is the ability to track the input signal variations and adapt to the changes of amplifier nonlinear characteristics. Other effects are included in the analysis such as quadrature modulator and demodulator impairments. A computer simulation has been carried out to verify method functionality.

LINC digital component separator for single and multicarrier W-CDMA signals

An implementation of a digital component separator for a linear amplification using nonlinear components (LINC) system on a field-programmable gate array is presented. It employs a flexible upconversion architecture, which can be easily configured as an image-reject or direct-upconversion architecture for transmission of single or combined multicarrier wireless code-division multiple-access (W-CDMA) signals and uses the phase-modulation method. Four direct digital synthesizers are applied as phase modulators, operating first on a low IF carrier varying from 0 to 1/4 of the sampling frequency. The sampling frequency can be chosen up to 32 times (122.88 MHz) the symbol rate of the W-CDMA chip rate of 3.84 Mbit/s. The system allows a flexible frequency assignment and spacing of one or two independent W-CDMA channels. This paper outlines how the envelope and phase information of two combined W-CDMA channels may be pre-calculated in real time. This information may be used for the generation of two phase-modulated signals, which are then supplied to a single LINC transmitter. The achieved performance is demonstrated for single and multicarrier application utilizing direct and/or image-reject upconversion including simulated and experimental data (adjacent channel power ratio, complementary cumulative distribution function, error vector magnitude).

LINC power amplifier combiner method efficiency optimization

Linear amplification using nonlinear components (LINC) is a method of vector summing two constant amplitude phase-modulated signals to achieve power amplification. The theoretical efficiency of the LINC power amplifier has been reported as 100% since highly efficient nonlinear constant amplitude amplifiers can be used. However, the 100% efficiency performance is only possible at one or two loads along the power output curve. The bulk of the papers regarding LINC has focused on clever implementations of the signal vector decomposition as well as methods to achieve highly linear signal separation. There has been little regard in the literature to the signal combiner implementation necessary to achieve the high power-added efficiency (PAE) of the LINC radio frequency (RF) power amplifier. Efficiency is not an intrinsic property of the combiner implementations, however, the combiner method is the single biggest contributor to efficient performance of a LINC RF power amplifier. This paper develops an analysis method that determines the efficiency of the LINC power amplifier as a function of the amplitude modulation statistics. This can be employed to design the RF communication system amplitude modulation characteristics and to tradeoff and optimize the RF transmitter PAE.