Amplitude-to-phase Modulation Research Articles

Design and Optimization of a Highly Linear Power Amplifier with Novel Active Bias Circuit in InGaP/GaAs HBT MMIC Technology

This paper introduces a highly linear power amplifier (PA) that utilizes a 2-μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process. As communication systems evolve in complexity, the demands for the linearity and static power consumption of HBT power amplifiers are becoming more stringent. Typically, there exists a trade-off relationship between linearity and static power consumption in the design process. Hence, this paper proposes a novel active bias circuit for HBT power amplifiers, along with its layout design. The proposed active bias circuit consists of a differential pair and a current mirror structure, designed to enhance PA linearity while maintaining low quiescent current. Additionally, a novel layout structure is implemented to achieve thermal coupling between the RF transistors and the active bias, further improving PA linearity. As a result of the implementation of the proposed active bias and layout structure, the PA demonstrates high linearity in both amplitude modulation to phase modulation (AM/PM) and amplitude modulation to amplitude modulation (AM/AM) performance, while simultaneously maintaining a low quiescent current. The three-stage PA prototype achieves notable performance metrics, including a peak gain of 32.6 dB at 5.6 GHz, gain flatness of ±0.5 dB from 5.15 GHz to 5.85 GHz, and P1dB of 32.1 dBm at a quiescent emitter current of 180 mA.

Amplitude Modulation to Phase Modulation Conversion in Photonic Bandpass Sampling Link

The photonic bandpass sampling has been proved to be potential in multi-carrier communication, frequency-agile coherent radar, compressive sensing, etc. It supports the direct down-conversion of multi-carrier signals using a low-speed analog-to-digital converter (ADC). We observed the distortion resulted from amplitude-modulation to phase-modulation (AM-PM) conversion caused by the saturated photo-detector in the photonic bandpass sampling link. The nonlinearity caused by the AM-PM conversion is theoretically analyzed, which is the 2nd harmonic distortion and has a phase difference of 90 degrees with the fundamental signal. Due to the AM-PM conversion, the 2nd harmonic distortion occurs even the Mach-Zehnder modulator (MZM) is quadrature biased in the photonic bandpass sampling link. Two comparative experiments were conducted to test the nonlinearity. When the MZM works at different bias points, the phase of the 2nd harmonic distortion will be different. In addition, we also compared the differences in 2nd harmonic distortion between standard continuous wave photonic links and photonic bandpass sampling links.

Conversion of amplitude modulation to phase modulation in the human cochlea

When an amplitude modulated signal with a constant-frequency carrier is fed into a generic nonlinear amplifier, the phase of the carrier of the output signal is also modulated. This phenomenon is referred to as amplitude-modulation-to-phase-modulation (AM-to-PM) conversion and regarded as an unwanted signal distortion in the field of electro-communication engineering. Herein, we offer evidence that AM-to-PM conversion also occurs in the human cochlea and that listeners can use the PM information effectively to process the AM of sounds. We recorded otoacoustic emissions (OAEs) evoked by AM signals. The results showed that the OAE phase was modulated at the same rate as the stimulus modulation. The magnitude of the AM-induced PM of the OAE peaked generally around the stimulus level corresponding to the compression point of individual cochlear input–output functions, as estimated using a psychoacoustic method. A computational cochlear model incorporating a nonlinear active process replicates the abovementioned key features of the AM-induced PM observed in OAEs. These results indicate that AM-induced PM occurring at the cochlear partition can be estimated by measuring OAEs. Psychophysical experiments further revealed that, for individuals with higher sensitivity to PM, the PM magnitude is correlated with AM-detection performance. This result implies that the AM-induced PM information cannot be a dominant cue for AM detection, but listeners with higher sensitivity may partly rely on the AM-induced PM cue.

An 0.4–2.8 GHz CMOS Power Amplifier With On-Chip Broadband-Pre-Distorter (BPD) Achieving 36.1–38.6% PAE and 21 dBm Maximum Linear Output Power

A broadband 180 nm CMOS power amplifier (PA) operating from a frequency bandwidth of 400 MHz to 2.8 GHz is presented in this paper. The PA is integrated with an inductor-less Broadband-Pre-Distorter (BPD) to enhance its linearity for wide bandwidth. The BPD consists only of MOS transistors, resistors, and capacitors which contribute to the wideband operation thus independent of the Q factor of passive inductors which contributes to the effectiveness of many other APDs available. The integrated BPD improves the Amplitude Modulation-to-Amplitude Modulation (AM-AM) and Amplitude Modulation-to-Phase Modulation (AM-PM) deviation of the PA across maximum linear output power of 21 dBm. Utilizing a silicon area of 1.69 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , mounted on Roger's RO4000/FR4 PCB, the BPD-PA produces a maximum output power of more than 22 dBm for 2.4 GHz bandwidth with a minimum power gain of 15 dB. The corresponding peak power added efficiency (PAE) of more than 35% is achieved across the operating bandwidth. The fabricated BPD-PA meets the Adjacent Channel Leakage Ratio (ACLR) specification of -30 dBc at a maximum linear output power of 21 dBm (3 dB back-off from maximum output power) when tested with 20 MHz LTE signal at 1.7 GHz.

A 31 GHz body-biased configurable power amplifier in 28 nm FD-SOI CMOS for 5 G applications

AbstractThis paper presents a 31 GHz integrated power amplifier (PA) in 28 nm Fully Depleted Silicon-On-Insulator Complementary Metal Oxide Semiconductor (FD-SOI CMOS) technology and targeting SoC implementation for 5 G applications. Fine-grain wide range power control with more than 10 dB tuning range is enabled by body biasing feature while the design improves voltage standing wave ratio (VSWR) robustness, stability and reverse isolation by using optimized 90° hybrid couplers and capacitive neutralization on both stages. Maximum power gain of 32.6 dB, PAEmax of 25.5% and Psat of 17.9 dBm are measured while robustness to industrial temperature range and process spread is demonstrated. Temperature-induced performance variation compensation, as well as amplitude-to-phase modulation (AM-PM) optimization regarding output power back-off, are achieved through body-bias node. This PA exhibits an International Technology Roadmap for Semiconductors figure of merit (ITRS FOM) of 26 925, the highest reported around 30 GHz to authors' knowledge.

Efficient 60-GHz Power Amplifier With Adaptive AM-AM and AM-PM Distortions Compensation in 65-nm CMOS Process

This article presents a 60-GHz CMOS power amplifier (PA) with an adaptive impedance-compensation linearizer in the 65-nm CMOS process. The proposed linearizer adaptively provides resistance and capacitance that vary appropriately with input power, enabling amplitude-to-amplitude modulation (AM-AM) and amplitude-to-phase modulation (AM-PM) distortions to be compensated simultaneously. The fabricated PA with linearizer on achieves a P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> dB of 12.3 dBm and a peak power-added efficiency (PAE) of 15.6% at such P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> dB, which demonstrate improvements of 2.8 dB and 6.8%, respectively, compared with the PA with linearizer off. The PA also achieves the peak gain of 31.0 dB, peak saturated power (PSAT) of 15.0 dBm, and peak PAEmax of 22.7%. In addition, the AM-AM distortion at 6-dB output back-off (OBO) is less than 0.1 dB, and the AM-PM distortion at P1 dB is less than 1.5° in the overall 3-dB frequency band. The improvements in both the AM-AM and AM-PM signals lead to a 1.7-dB improvement in OBO at third-order intermodulated distortion of -25 dBc without adding to power consumption.

Characterization of AM-to-PM Conversion in Silicon p-i-n Photodiodes

We have measured the amplitude-to-phase modulation (AM-to-PM) conversion in a silicon p-i-n photodiode for the first time and found that it behaves qualitatively similar to III-V detectors previously reported in the literature. One or more minima in the AM-to-PM conversion gain as a function of average photocurrent was seen and the minima were found to depend on the reverse bias, suggesting that space charge fields produced by the separating carriers interact with the applied reverse bias and modulate the drift velocities and hence the transit times.

Study the Mechanism and Suppression of AM/PM Conversion of Traveling-Wave Tubes Using Eulerian Hydrodynamic Analysis

In this paper, the fourth-order analytic solution of amplitude modulation to phase modulation (AM/PM) conversion is first derived from an Eulerian nonlinear analytic model. The analytic relationships between electron phases, detuning parameter b, and AM/PM conversion are also found. Then, the mechanism of AM/PM conversion is studied. It is found that the generation of the harmonics in the dc component of the electron phase in the nonlinear beam–wave interaction region is the main mechanism of AM/PM conversion. Next, a series of AM/PM conversion suppression schemes is discussed by using the mechanism. The Eulerian formations are validated by an in-house code based on the Lagrangian theory. Results show that the fourth-order analytic solution of normalized axial electric field and AM/PM conversion agree well with the Lagrangian theory in the nonlinear region. In addition, the suppression schemes are applied to a high-efficiency Ku-band space traveling-wave tube (TWT). The AM/PM conversion distortion is greatly reduced by approximately 50% with a slight drop of output power. We hope that our efforts will help the nonlinear design of TWT in the future.

Dynamic Feedback Linearizer of RF CMOS Power Amplifier

A dynamic feedback linearizer for an RF CMOS power amplifier (PA) is presented, which consists of a negative feedback network and a dynamic feedback control circuit to inject a reshaped envelope signal to the network. The linearizer compensates for the gain compression of the RF CMOS PA in high-power region by reducing the feedback dynamically, and it also reduces the amplitude-to-phase modulation (AM-PM) distortions. The PA including the linearizer was fabricated using a 0.18- $\mu \text{m}$ RF CMOS process, which has an output transmission-line transformer on a printed circuit board. It delivers an output power of 28.1 dBm at 1.7 GHz with power added efficiency of 40.9%, and adjacent channel leakage ratio (ACLR $_{\mathrm {E-UTRA}}$ ) of under −30 dBc for a 10-MHz 16-QAM long-term evolution signal without digital predistortions.

High-sensitivity optical to microwave comparison with dual-output Mach-Zehnder modulators

We demonstrate the use of two dual-output Mach-Zehnder modulators (DO-MZMs) in a direct comparison between a femtosecond (fs) pulse train and a microwave signal. Through balanced detection, the amplitude-to-phase modulation (AM-PM) conversion effect is suppressed by more than 40 dB. A cross-spectrum technique enables us to achieve a high-sensitivity phase noise measurement (−186 dBc/Hz above 10-kHz offset), which corresponds to the thermal noise of a +9 dBm carrier. This method is applied to compare a 1-GHz fs monolithic laser to a 1-GHz microwave signal generated from photodetection of a free-running 500 MHz mode-locked laser. The measured phase noise is −160 dBc/Hz at 4-kHz, −167 dBc/Hz at 10-kHz, and −180 dBc/Hz at offset frequencies above 100-kHz. The measurement is limited by the free-running 500-MHz laser’s noise, the flicker noise of the modified uni-traveling carrier photodiode and the thermal noise floor, not by the method itself. This method also has the potential to achieve a similar noise floor even at higher carrier frequencies.

An Optimized Segmented Quasi-Memoryless Nonlinear Behavioral Modeling Approach for RF Power Amplifiers

This paper presents an optimized segmented modeling approach using a new quasi-memoryless (QM) behavioral model (BM) that allows for RF power amplifier (RF PA) modeling over a range of different solid state PA technologies. The presented model is a combination of an existing semiphysical amplitude-modulation-to-amplitude-modulation (AM/AM) memoryless BM, which correctly predicts third-order intermodulation distortion (3rd IMD) response in the small signal region, with the newly proposed amplitude-modulation-to-phase-modulation (AM/PM) model derived from the existing AM/AM model. Using the segmentation and optimization methods, performance comparisons with this new model are presented, showing normalized mean squared error AM/PM improvements up to 20 dB, as well as over 5-dB improvement in predicting the 3rd IMD using the proposed model. Comparisons against other well-known QM BMs are conducted using measured data as well as with data presented in the literature. The effects of these improvements on linearizer performance are also evaluated. The model significantly improves system-level modeling by allowing designers to accurately predict system performance using various RF PA devices over a range of technologies, based on data available through manufacturers’ data or simple tests.

21.3 dBm 18.5 GHz‐BW 8‐way E‐band power amplifier in 28 nm high performance mobile CMOS

A fully integrated broadband E-band power amplifier (PA) is implemented in 28 nm CMOS process. To enhance the output power (P OUT), an 8-way differential series-parallel power combiner is used together with the neutralised bootstrapped cascode amplifier topology. The unit PAs are realised by both NMOS and PMOS transistors, respectively, which cancel the amplitude-to-phase modulation (AM-PM) distortion due to non-linear gate-to-source capacitance (C GS) of NMOS and PMOS transistors under large input voltage amplitude. The presented PA achieves a saturated output power (P SAT) of 21.3 dBm with more than 18.5 GHz −3 dB small-signal bandwidth (BW−3 dB).

Self-group-velocity modulation and AM-to-PM conversion in optical rectification

Optical rectification as a detection technique does not suffer from the nonlinearity, saturation and large amplitude-to-phase modulation (AM-to-PM) conversion effects exhibited by semiconductor carrier-based photodiodes. In this paper we analyze the effect of self-group-velocity modulation as a mechanism for AM-to-PM conversion in traveling-wave optical rectification detectors (ORDs) and derive a closed-form expression for the AM-to-PM conversion gain. For a small signal amplitude modulation index m, we find the induced phase modulation index βi on the nonlinear polarization wave due to a train of femtosecond optical pulses in a bulk LiNbO3 traveling-wave ORD to be βi<3×10−8 m or βi/m≈−151 dB. Cascaded χ(2) processes as well as the thermo-optic effect are also considered with the former producing conversion gain comparable to direct χ(3) while the latter is four orders of magnitude smaller.

Characterization of Amplitude Noise to Phase Noise Conversion in Charge-Compensated Modified Unitravelling Carrier Photodiodes

The phase noise, i.e., amplitude modulation to phase modulation (AM-PM) in the photodetector. In general, AM-PM of charge-compensated modified uni-travelling carrier (CC-MUTC) photodiodes originates from the combined nonlinearities of the detector impedance and carrier transit times, which depend on the electric field distribution and the velocity-field characteristics of carrier transport. In this work, we report measurements of AM-PM in transit-time-limited CC-MUTC photodiodes. A Crosslight-based simulation of the photodetection process is used to quantitatively estimate the AM-PM of CC-MUTC photodiodes. Simulated AM-PM of a 15-GHz microwave signal shows good agreement with experimental results. The measured and simulated AM-PM versus photocurrent exhibit a null point that originates from the competition between hole deceleration due to the collapsed electric field in the depleted absorption region and electron acceleration in the self-induced electric field in the undepleted absorption region.

A 60-GHz Power Amplifier With AM–PM Distortion Cancellation in 40-nm CMOS

This paper presents a complementary push-pull 60-GHz power amplifier (PA) in 40-nm CMOS. The proposed technique is used to mitigate the amplitude to phase modulation (AM-PM) distortion caused by the nonlinear input capacitance of an MOS transistor. By operating in deep class-AB mode, the back-off efficiency of the PA is improved without compromising gain. The proposed interstage transformer with two secondary windings enables right impedance transformation concurrently for the two separate transistors with independent biasing ability. The two-stage PA achieves a gain of 22.4 dB, power added efficiency (PAE) PAEMAX of 23%, and saturated output power ( $P_{\text {SAT}}$ ) of 16.4 dBm with 8% PAE at 6 dB back-off. With 35 dB of adjacent channel power ratio. Also a comparison with a common-source PA is presented, which shows its limitation in dealing with AM-PM distortion.

A Memoryless Semi-Physical Power Amplifier Behavioral Model Based on the Correlation Between AM–AM and AM–PM Distortions

A new semi-physical memoryless computationally effective behavioral model (BM) capable of predicting amplitude-modulation-to-amplitude-modulation (AM-AM) and amplitude-modulation-to-phase-modulation (AM-PM) distortions is proposed. In recent years, AM-AM and AM-PM distortions have been separately studied in literature. Here, we investigate the correlation between AM-AM and AM-PM distortions first. Based on the observed correlation, a novel AM-PM model is derived from the well-known Rapp AM-AM model. On the basis of the close relationship between the AM-AM and AM-PM model, a highly accurate and computationally effective large-signal BM is obtained. The newly developed model addresses the current needs of the mobile industry that requires BMs of the power amplifier (PA), which can be interpreted by the designers. In addition, the models must be computationally effective due to the limited computation power in mobile handset. Therefore, only memoryless BMs can be taken into account and larger errors are accepted for the sake of computational effectiveness. In this paper, it is shown that the newly introduced model achieves excellent results, when it is applied to actual industrial applications of two GaAs-based class-AB PAs in 65-nm technology and one CMOS-based class AB PA in 28-nm technology, which are designed for mobile communications.

A simple and reliable technique to characterize amplitude to phase modulation distortion for high-frequency amplifiers and nonlinear devices

This paper presents a simple and reliable measurement system for characterizing the amplitude to phase modulation (AM-PM) characteristics of high frequency amplifiers and nonlinear devices. The AM-PM measurement system is based on a null detector implemented with a double balanced mixer, and requires a voltmeter and a calibrated phase shifter. A 12 W class A radio frequency power amplifier has been designed using a GaN transistor, and the AM-PM has been measured using both the method proposed in this work and the classical method with a calibrated vector network analyzer. A good correlation between both methods is observed, which validates the proposed method.

A linear-high range output power control technique for cascode power amplifiers

In this paper a new linear power control technique is presented to control the output power of cascode power amplifiers. Using this technique the output power of power amplifier can be controlled from the maximum output power to −136 dBm, continuously. The characteristic of the output voltage versus control voltage is linear from −15.9 to 18.6 dBm (a range of 34.5 dB) of the output power. Also at this range the Amplitude Modulation to Phase Modulation (AM-PM) distortion is 43°. Furthermore, the input dynamic range is 0.373 V, which is less than the conventional techniques. Having a power controller in a low power path and a low input dynamic range leads to minimizing the controller dissipation and reduction of power added efficiency (PAE). The proposed technique is simulated using 0.13 μm CMOS process model using Advanced Design System and the results obtained are presented.

A Multiport Measurement System for Complex Distortion Measurements of Nonlinear Microwave Systems

An effective multiport measurement system for the characterization of N-port nonlinear microwave devices is proposed. The proposed measurement system has the capability of measuring the S-parameters of linear microwave circuits and the amplitude-modulation-to-amplitude-modulation (AM/AM) and amplitude-modulation-to-phase-modulation (AM/PM) conversions for fundamental and harmonic frequencies for nonlinear microwave devices on single-step measurement without any need for reconnection or change in the calibration technique or measurement setup. It is found suitable that the proposed system can accurately quantify the impact of crosstalk on the performance of multibranch amplifiers and multiport nonlinear microwave systems in terms of power efficiency and signal distortion.

Nonlinear behavioral of GaN Doherty power amplifiers using neural modeling

AbstractA radial‐basis function neural network (RBFNN) approach is proposed for predicting the nonlinear behaviors of gallium nitride (GaN) Doherty amplifier. Sampled input and output data from a designed GaN Doherty amplifier were used to train and test the proposed RBFNN model. Comparison of amplitude modulation to amplitude modulation (AM/AM), amplitude modulation to phase modulation (AM/PM), gain, power added efficiency (PAE) and output power (Pout) curves among the RBFNN method, circuit simulation and measurement are given. The results indicate that the proposed RBFNN model can reproduce the nonlinear characteristics of the designed GaN Doherty amplifier accurately. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 307–309, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24924