AM-PM Characteristics Research Articles

A Linear Millimeter-Wave GaN MMIC Doherty Power Amplifier With Improved AM-AM and AM-PM Characteristics

A Linear Millimeter-Wave GaN MMIC Doherty Power Amplifier With Improved AM-AM and AM-PM Characteristics

A 28-GHz CMOS Power Amplifier Linearized by Dynamic Conductance Control and Body Carrier Injection

A 28-GHz linear CMOS cascode power amplifier (PA) that adopts two types of analog linearization methods, dynamic conductance control (DCC) and body carrier injection (BCI), is presented here. The former method controls the load conductance of a common-source (CS) amplifier according to the input power of the PA. This improves the AM-AM and AM-PM characteristics of the cascode PA, which is also analyzed with an equivalent circuit model. The latter injects the carrier signal into the body of a common-gate (CG) transistor, which increases the voltage headroom of the CS transistor. This improves the AM-AM of the cascode PA and also helps to stabilize the PA by reducing the drain-source capacitance of the CG transistor. The proposed PA is fabricated in a 65-nm CMOS process and shows a gain of 15.9 dB, an output 1-dB compression point of 17.7 dBm, and a saturation output power of 19.1 dBm with a peak power-added efficiency (PAE) of 41.2% at 28 GHz.

28-GHz CMOS Power Amplifier Linearized With Resistive Drain-Body Connection

A 28-GHz two-stage differential cascode power amplifier (PA) linearized with a simple common-source (CS) body network, in which the body of the CS amplifier at the power stage is connected to the drain through a large resistance. The body network is very simple but very effective to linearize the PA. The linearity improvements are explained and shown with the intermodulation distortions (IMD3) and AM-PM characteristics. The PA also shows a wideband gain because the matching networks consist mainly of transmission-line transformers (TLTs) and distributive interstage matching. It has a gain of 20.1 dB with a bandwidth of 10.8 GHz, a saturation output power of 20.25 dBm, and an output 1-dB compression point of 18.3 dBm, which is fabricated in a 40-nm bulk CMOS process with the area of 0.214 mm 2 .

A 28-GHz Beamforming Doherty Power Amplifier With Enhanced AM-PM Characteristic

This article presents a beamforming Doherty power amplifier (B-DPA) for the 28-GHz fifth-generation (5G) new-radio band. The proposed B-DPA is based on a new combiner topology that allows the current profile in the auxiliary branch of the DPA to be relaxed while simultaneously canceling the amplitude-to-phase (AM-PM) distortion exhibited in the active devices. This approach enables efficiency and linearity enhancements. In addition, the DPA is augmented with high-accuracy digitally assisted vector multipliers at its input stage to provide the required relative and absolute phase adjustments for proper Doherty operation and the overall phase shift required for beamforming. A proof-of-concept prototype was implemented in the 45-nm silicon on insulator (SOI)-CMOS technology. Measurement results reveal that the proposed B-DPA demonstrated good Doherty operation with drain efficiencies of 18%–20% and 33%–35% at 6-dB back-off and saturation power (Psat, 18 dBm) levels, respectively, between 28 and 30 GHz. In particular, excellent AM-PM characteristics were noted with a peak value of only 1.5° up to Psat, which remained below 2.5° as the B-DPA was swept with a 0° to 360° phase shift. Finally, modulated-signal tests revealed error vector magnitudes of 3.1% and 0.9% for 4-MHz $\times100$ -MHz orthogonal frequency division multiplexing (OFDM) signals before and after applying digital predistortion, respectively.

Behavioral Modeling of GaN Doherty Power Amplifiers Using Memoryless Polar Domain Functions and Deep Neural Networks

In this paper, novel Doherty Power Amplifier (DPA) models are presented. The motivation behind the proposed models is to accurately predict static nonlinearities in the compression regions of the carrier and peaking amplifiers. DPAs suffer from a nonlinearity that originates from the carrier amplifier, and a second more pronounced nonlinearity generated at the full compression region following the turn-on of the peaking amplifier. Moreover, these distortions are often observed at different input power levels depending on whether the AM-AM or the AM-PM characteristic is considered. Therefore, the proposed static model is based on independent modeling of the memoryless gain in the polar domain. The static model of the memoryless AM-AM and AM-PM characteristics is augmented with either memory polynomials or deep neural network functions for memory effects modeling. The methodology of building the proposed models and the achieved results are discussed in this paper. The MP based proposed model achieves an NMSE as low as -45.3dB with only 78 model parameters, while the DNN based model achieves an NMSE as low as -46.1dB with only 156 model parameters. However, the DNN based model achieves the best model resilience to changes in the identification data.

Linearity-Enhanced Doherty Power Amplifier Using Output Combining Network With Predefined AM–PM Characteristics

In this paper, a new method is proposed to synthesize a linearity-enhanced Doherty power amplifier (DPA) without deteriorating its efficiency. This method determines the combiner network parameters so that a predefined amplitude-to-phase (AM–PM) characteristic is produced while maintaining proper load modulation and consequently good back-off efficiency. The predefined AM–PM characteristic is chosen to be the inverse of the main transistor to enhance the overall DPA linearity. For proof-of-concept validation purposes, a linearity-enhanced DPA circuit prototype is designed to provide linear overall AM–PM characteristics over the frequency band of 4.7–5.3 GHz. Meanwhile, its input matching network is designed to minimize the amplitude-to-amplitude (AM–AM) distortion by properly selecting the source impedances. The measurement results of the DPA prototype under continuous-wave stimuli reveal AM–PM and AM–AM characteristics with maximum phase and gain compression/expansion below ±1° and ±0.25 dB, respectively, when the input power level is swept up to a saturation level of 39 dBm over 4.9–5.3 GHz. Furthermore, when driven with carrier aggregated signals with modulation bandwidths of up to 160 MHz and a peak-to-average power ratio equal to 7.4 dB, the DPA prototype maintains an adjacent channel leakage ratio of better than −40 dBc with a drain efficiency in the excess of 40% and an average output power of 32 dBm, without resorting to any additional linearization schemes. The proposed DPA methodology paves the road for the application of the DPA technique to 5G massive multiple-input and multiple-output transmitters with relaxed linearity requirements as it avoids the extra complexity and power consumption overhead associated with dedicated linearization schemes.

Behavioral Model of Power Amplifier Using a Discrete-Time Impulse Response Representation

Broadband transfer functions of radio frequency (RF) power amplifiers (PA) can be developed from the frequency-dependent AM-AM and AM-PM characteristics of the PAs. The time-domain representation of these broadband transfer functions proposed in this letter can be viewed as a PA behavioral model. This PA behavioral model is capable of instantaneously convolving with multi-tone input signals to produce output signals. When compared to conventional quadrature models, which are also based on the measurement of AM-AM and AM-PM characteristics, experiments show the proposed model to be more accurate and efficient in broadband PA behavioral modeling.

Low-complexity, full-resolution, mirror- switching digital predistortion scheme for polar-modulated power amplifiers

Proposed is a mirror-switching digital predistortion (DPD) scheme with low complexity and full resolution, tailored for power-efficient polar-modulated power amplifiers with nonlinear AM-AM and AM-PM characteristics. The involved digital circuitry is composed of just one CORDIC operator and two 1D look-up tables, avoiding any real-time interpolation or analogue operation. The DPD scheme is verified on a FPGA and the estimated power using a 65 nm CMOS technology is 5.2 mW. The training time is ∼82 µs at a clock rate of 100 MHz. System-level simulations in MATLAB show significant improvements of error vector magnitude from 104.8 to 2%, and adjacent channel leakage ratio from 21.36 to 49.27 dB, under a 20 MHz-bandwidth 64-QAM OFDM test signal.

Analysis on dynamic characteristics of reflective semiconductor optical amplifier based on a memory polynomial model

This article presents the AM–AM and AM–PM characteristics of a bulk reflective semiconductor optical amplifier (RSOA) based on a memory polynomial model. The coefficients of the behavioral model are extracted and validated by experimental results. The nonlinearity and memory effects of RSOA are demonstrated by its dynamic AM-AM and AM-PM characteristics. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:805–808, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26636

A Distortion-Cancelled Doherty High-Power Amplifier Using 28-V GaAs Heterojunction FETs for W-CDMA Base Stations

An L/S-band 330-W distortion-cancelled Doherty GaAs field-effect transistor (FET) amplifier has been successfully developed optimizing the main and peak amplifiers load impedance shift. The amplifier employed a pair of 28-V operation 150-W GaAs heterojunction FETs. It demonstrated low third-order intermodulation of -37 dBc with a drain efficiency of 42% at an output power of 49 dBm around 6-dB backoff level under the two-carrier wideband code-division multiple-access (W-CDMA) signals of 2.135 and 2.145 GHz. To our knowledge, these represent the best results ever reported among the simple high-power FET amplifiers for W-CDMA base stations. In addition, we proposed the evaluation techniques to obtain each AM-AM and AM-PM characteristics of the main and peak amplifiers in an operating Doherty amplifier, and have experimentally proven the distortion cancellation effect in the GaAs FET Doherty amplifier

OFDM Error Vector Magnitude Distortion Analysis

We derived explicit formulas for evaluating the error vector magnitude (EVM) from the amplitude distortion (AM-AM) and phase distortion (AM-PM) of power amplifiers (PAs) in orthogonal frequency-division multiplexing (OFDM) systems, such as the IEEE 802.1 1a/g wireless local area networks (WLANs) standards. We demonstrated that the developed formulas allowed EVM simulation of a memoryless PA using only a single-tone response (i.e. without OFDM modulation and demodulation), thus enabling us to easily simulate the EVM using a harmonic-balance (HB) simulator. This HB simulation technique reduced the processing time required to simulate the EVM of a PA for the IEEE 802.1 1a standard by a factor of ten compared to a system-level (SL) simulation. We also demonstrated that the measured EVM of a PA module for the IEEE 802.11g could accurately be predicted by applying the measured static AM-AM and AM-PM characteristics to the derived formulas.

Effects of nonlinear distortion on CDMA communication systems

We report a rigorous approach to analyze the effects of nonlinear distortion on code division multiple access (CDMA) wireless communication systems based on time-domain analysis and band-pass nonlinearity theory. Given AM-AM and AM-PM characteristics of a nonlinear device, this technique is capable of predicting adjacent channel power rejection (ACPR), noise power ratio (NPR), two-tone intermodulation products, CDMA waveform quality, and baseband signal vector constellation at the output of the nonlinear device. To demonstrate and verify the capability of this technique, an L-band power amplifier was designed, built, tested with CDMA waveforms, and compared with the simulated results. Excellent agreement between the measured and predicted results has been achieved.

Performance evaluation of non-linear transmit power amplifiers for North American digital cellular portables

This paper discusses the system performance degradation resulting from using a non-linear transmit power amplifier (PA) in a North American digital cellular (NADC) portable radio. The NADC portables require a linear power amplifier for the spectrally efficient linear modulation scheme, /spl pi//4-DQPSK. It is well known that these PA's can exhibit non-linear characteristics that degrade system performance. System degradation is measured using bit error rate (BER) as the figure of merit. The PA is modeled by its AM-AM and AM-PM characteristics; the receiver architecture contains the simple, yet robust, differential detector. Simulation results are presented for additive white Gaussian noise (AWGN), Rayleigh fading, and frequency selective fading environments, and compared to results for a truly linear PA. In addition, PA spectral regrowth is discussed as well as the potential use of a linearization technique to compensate for the PA effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Modified Barrett-Lampard Expansion and Its Application to Bandpass Nonlinearities with Both AM-AM and AM-PM Conversion

A two-dimensional Barrett-Lampard expansion is developed to handle two-dimensional nonlinear systems with random Gaussian inputs. The theory is applied to the problem of evaluating the mean signal and the inphase and quadrature noise correlation functions at the output of a TWT nonlinearity exhibiting arbitrary AM-AM and AM-PM characteristics, when the input consists of a narrow-band signal and Gaussian noise. As a specialized application, the classical problem of determining the coherent and incoherent noise correlation functions at the output of a power-law bandpass nonlinearity is also considered. The results are of interest in assessing the performance of coherent satellite communication channels. The theory developed is accompanied by numerical examples of practical interest.