Adjacent Channel Power Ratio Performance Research Articles

A Frequency-Selective Digital Predistortion Method Based on a Generalized Indirect Learning Architecture

Frequency-selective (FS) digital predistortion (DPD), which focuses on suppressing the nonlinear distortion at a specific band, has gained increased interest in recent years. However, there is a lack of a general FS DPD approach that is applicable to most scenarios and is suitable for practical implementation. This paper proposes an FS DPD method based on a generalized indirect learning architecture (GILA). Our work on this GILA-based FS DPD method is composed of two contributions. First, an FS Volterra series model structure, which consists of a basic linear part and a partial-band pre-compensation part, is proposed to construct an FS predistorter. Second, a GILA-based identification method is proposed to extract coefficients of the FS predistorter with the FS Volterra series model structure. The proposed GILA-based FS DPD is a general method with low complexity for implementation. Both simulations and experiments verify that the target band of the DPD linearization is arbitrary for the proposed GILA-based FS DPD method. As a special case, when using the proposed method to focus on suppressing the out-of-band distortion, the adjacent channel power ratio performance of the proposed method can be 7.1 dB better than that of the conventional full-band DPD.

Investigation on harmonic spur characteristics of hybrid integrated LDMOS and AlGaN / GaN power amplifiers at different temperatures

The harmonic spur characteristics of a hybrid integrated S-band power amplifier (PA), consisting of both stages of LDMOSFET and AlGaN/GaN HEMT, are studied at different temperatures. The PA offers a peak output power of 50 dBm (100 W) with power added efficiency higher than 50%, and adjacent channel power ratio performance is less than −30 dBc. A temperature test chamber is employed for measuring the harmonic spur of PA from 233 to 393 K, and its linear response to temperature is captured at high output power level.

A Square-Root-Based Memory Polynomial Model for Concurrent Dual-Band Digital Predistortion

In this letter, a novel 2-D square-root-based memory polynomial behavioral model is proposed. A new set of square-root-based basic functions is adopted to describe the characteristic of the predistorter. Since the proposed model has only two nested summations, the number of coefficients of the proposed model is greatly reduced compared with models which have three nested summations. The experimental results show that the proposed model can reduce the coefficients by more than 66.7% compared with the 2-D digital predistortion (2D-DPD) model. Moreover, the proposed model can achieve better adjacent channel power ratio (ACPR) performance. Compared with the 2D-DPD model and the simple online coefficient update model, the proposed model can improve the normalized mean-square error by 11 dB. Compared with the 2-D modified memory polynomial model, the proposed model can obtain similar ACPR performance with a shorter running time.

Model order selection for digital predistortion of a RF power amplifier when the distortion spectrum exceeds the observation bandwidth

Digital predistortion (DPD) of a nonlinear power amplifier (PA) is made challenging when the observation bandwidth (OBW) used to measure the output signal is narrower than the intermodulation distortion (IMD) spectrum generated. Wide bandwidth input signals stimulate memory effects within the PA thereby requiring the model order of the DPD to be expanded to include memory correction coefficients. However, if the model order is over-specified relative to the OBW, the estimation of the DPD coefficients will be ill-conditioned and the distortion cancellation will be degraded. This paper proposes a method of selecting the best model order of the DPD coefficient estimation for the available OBW. Adjacent channel power ratio (ACPR) is used as an independent measure of the distortion cancellation for a given model order. Experimental results demonstrate the relationship between the model order of the estimation, the OBW, and the ACPR performance of the wide bandwidth IMD cancellation.

A CMOS Outphasing Power Amplifier With Integrated Single-Ended Chireix Combiner

This brief proposes an on-chip outphasing power amplifier that uses a single-ended Chireix combiner for a linear amplification with a nonlinear component amplifier. The proposed combiner structure consists of a lumped inductor and a lumped capacitor that can achieve the simple single-ended configuration of a Chireix combiner. It is also suitable for on-chip implementation with minimum efficiency deterioration. An inductance-capacitance balun using the lumped model of λ/4 and 3λ/4 transmission lines was effectively merged into a simple Chireix combiner for two outphased input signals. The relation between the output resistance and the outphasing angle of the input signals was derived to determine the maximum efficiency. A voltage-mode class-D power amplifier was used with the combiner to illustrate the combiner's effectiveness. The prototype fabricated in a 0.13-μm complementary metal-oxide-semiconductor process shows a maximum 52% power-added efficiency (continuous wave) and a -47-dBc adjacent channel power ratio performance at a 10-MHz offset with a 1.92-GHz wideband code-division multiple-access signal.

A Rigorous Study of Package and PCB Effects on W-CDMA Upconverter RFICs

A Volterra-series analysis is presented to study the package and printed circuit board (PCB) effects on the linearity of two wideband code-division multiple-access upconverter RF integrated circuit (RFIC) designs. The first design adopts a recently popular micromixer with a class AB input stage. The second design is based on a commonly used Gilbert mixer with emitter degeneration. Both upconverter RFICs are designed to have the same adjacent channel power ratio (ACPR) in the chip-level simulation. After fabrication, packaging, and testing on the PCB, the micromixer-based design consumes less direct current, but causes more degradation in the ACPR performance due to the influence of package and PCB when compared to the Gilbert mixer-based design. The theoretical analysis indicates that the micromixer-based upconverter RFIC is rather susceptible to the parasitic effects from the ground interconnect and, therefore, it needs a better package solution with a lower ground inductance for practical use. Comparison between theory and measurement shows good agreement in predicting the variations of conversion gain and ACPR due to the presence of the package and PCB

Piecewise Pre-Equalized Linearization of the Wireless Transmitter With a Doherty Amplifier

This paper describes a predistorter (PD) based on piecewise pre-equalizers for use in multichannel wideband applications. The predistortion linearizer consists of piecewise pre-equalizers along with a look-up-table-based digital PD that together compensate for nonlinearities, as well as memory effects of power amplifiers (PAs). It takes advantage of multiple finite-impulse-response filters that significantly reduce the complexity when compared to memory polynomial methods. The proposed method was also compared with the conventional Hammerstein structure. A 300-W peak envelope power Doherty PA was first modeled by measured time-based samples in order to verify the adjacent channel power ratio (ACPR) performance in simulation using a multitone and single wideband code-division multiple-access (W-CDMA) carrier. Furthermore, the experimental results applying two W-CDMA carriers verify that the proposed method provided similar improvement to that of the memory polynomial approach. The experimental results verified the complexity reduction and superior ACPR performance over the conventional Hammerstein structure