Multistage Power Amplifiers Research Articles

A 376 kW narrow-linewidth pulsed fiber laser based on PRBS

When designing a fiber laser, it is difficult to achieve both narrow linewidth and high power due to nonlinear effects, especially stimulated Brillouin scattering (SBS). However, using the pseudo-random binary sequence (PRBS) phase modulation technique, SBS can be effectively suppressed in narrow-linewidth fiber lasers during amplification. In light of this, we carried out the experimental research described in this paper. First, based on a theoretical analysis, a narrow-linewidth linearly polarized pulsed fiber laser system was designed; then, an experimental platform of a multistage master-oscillator power amplifier (MOPA) structure was constructed, including one-stage continuous optical amplification and four-stage pulsed optical amplification. In our experiments, without phase modulation, a linearly polarized narrow-linewidth fiber laser achieved an average power output of 17 W and a peak power of 188 kW (repetition frequency of 10 kHz, pulse width of 8.5 ns). At this level of power, the spectral signal-to-noise ratio was about 40 dB, and the beam transmission factors in the X and Y directions were 1.14 and 1.11, respectively. Using PRBS phase modulation, a linearly polarized narrow-linewidth pulsed laser achieved an average power output of 30 W and a peak power of 376 kW (repetition frequency of 10 kHz, pulse width of 7.5 ns) at a clock rate of 1.25 GHz. The polarization extinction ratio was greater than 15 dB, the spectral signal-to-noise ratio was greater than 40 dB, and the beam transmission factors in the X and Y directions were 1.18 and 1.12, respectively.

C‐band 180‐nm CMOS transmitter front‐end with a three‐stage power amplifier for phased array applications

AbstractA fully differential transmitter front‐end with multistage power amplifiers and a 7‐bit phase shifter were implemented in a 180‐nm CMOS process. RC feedback and cross‐coupling circuits were adopted to improve the stability of the power amplifiers. For the final power stage, a four‐transistor in‐parallel architecture was used to obtain a large total gate width, while maintaining a compact size with relatively small parasitic effects. The measured saturated output power (Psat) of the fabricated transmitter chip is 21.3−22 dBm, with a system efficiency of 24%−28.2% at 5−7 GHz, and the root‐mean‐square phase and gain error are below 1.40° and 0.28 dB, respectively, with 7‐bit phase resolution.

Eighty nine‐watt cascaded multistage power amplifier using gallium nitride‐on‐silicon high electron mobility transistor for L‐band radar applications

This work presents a gallium nitride (GaN) high electron mobility transistor (HEMT)–based cascaded multistage power amplifier (MPA) in class-AB for L-band radar applications. The purpose of this endeavour is to develop an MPA using GaN HEMT devices to achieve optimised parameters such as high gain, high power, better efficiency, and linearity in a compact size. In an MPA design with multiple stages, oscillations are common owing to unwanted high gain at the lower frequency range. To overcome this issue, we introduced interstage harmonic termination networks as a novel approach to suppress high gain at low frequencies, which are prone to oscillations. The proposed cascaded MPA provides the maximum radio-frequency output power of 89 W and a power gain of 52 dB with an associated power-added efficiency of 51%. Second and third harmonic levels are −32.5 and −37 dBc, respectively. Two-tone measurements are performed with a frequency separation of 10 MHz, and an intermodulation level of less than −33 dBc is achieved.

Design of a miniaturized planar microstrip Wilkinson power divider withharmonic cancellation

In this paper, a compact microstrip Wilkinson power divider is designed and proposed using rectangularshaped resonator cells. The presented resonator cells are used instead of quarter-wave length branches in the traditional structure to reduce the circuit size, increase the bandwidth, and eliminate the unwanted harmonics. The designed resonator behavior is studied analytically and the locations of transmission zeros are investigated using transfer function andLCequivalentcircuitmethods. The proposed power divider(PD)operates at 2GHz frequency and suppresses the 2nd to 14th unwanted harmonics. The proposed PD achieves approximately 50% size reduction and 40%fractional bandwidth (FBW). The abilities of desirable size reduction and harmonic suppression along with simple structure and wide FBW make the proposed divider a good choice for the modern communication systems, such as multistage power amplifier applications. The proposed divider is implemented and measured. The measurement results verify the simulation responses.

Memory aware physically enhanced polynomial model for PAs

In this study, a new behavioural model named memory aware physically enhanced polynomial model is proposed. This modelling approach is based on using a physical analysis of the power amplifier (PA) operation and takes into account the electro-thermal and electrical memory effects as main sources of long-term memory. The physical analysis-based approach allows to select the most relevant coefficients for the model and discards the less significant ones in order to minimise the complexity. In this study, the proposed methodology is demonstrated on a single-stage class-AB PA. Nevertheless, it is applicable for multi-stage PAs. The model accuracy and complexity are evaluated using measurement results from two commercial PAs. Compared to the conventional memory polynomial (MP) model, for, respectively, 20 and 80 MHz long-term evolution signals, the proposed model shows 3 and 5 dB improvement in the normalised mean square error with fewer coefficients 18 instead of 20 for a memory depth of 3. Also, with same accuracy the proposed model has considerably fewer coefficients compared with the PLUME and generalised MP (GMP) models. Applying digital predistortion (DPD), the proposed model outperforms the MP model in terms of performance and the PLUME and GMP models in terms of complexity.

In-Circuit Characterization of Low-Frequency Stability Margins in Power Amplifiers

Low-frequency resonances with low stability margins affect video bandwidth characteristics of power amplifiers. In this paper, a non connectorized measurement technique is presented to obtain the low-frequency critical poles at internal nodes of a hybrid amplifier. The experimental setup uses a high-impedance probe connected to a vector network analyzer to obtain a fully calibrated closed-loop frequency response that is identified to get the poles of the device at low frequency. Compared to previous connectorized solutions, the approach avoids the ad hoc insertion of extra RF connectors to access the low-frequency dynamics of the amplifier. In addition, it simplifies the characterization at multiple internal nodes, which is worthwhile for an efficient detection and fixing of critical low-frequency dynamics in multistage power amplifiers. The technique is first applied to dc steady-state regimes and compared to the connectorized approach on a single-stage amplifier. Next, it is applied to a three-stage amplifier to show its potential to detect the origin of the undesired dynamics and the most effective way to increase stability margin. Finally, the technique has been extended to the large-signal case to increase its usefulness for the design and diagnosis of high-power amplifiers.

Technique to characterise transient behavioural of multistage RF power amplifier for two‐way radio applications

A new technique to characterise the behavioral response of multistage RF power amplifier (PA) is presented. A simplified design methodology of closed loop PA with DC current sensing of multistage PA (cascaded) and voltage shaping algorithm is introduced in this study. An accurate characterisation of transient behavioral which includes ramping of RF energy from noise level to steady state level and adjacent channel transient power (ACTP), shows a high degree of correlation with measurement level for wideband RF PA operation (400-520 MHz). A prototype board is fabricated and measurement results demonstrated good correlation with transient behavioral model simulation. On board measurements demonstrated transient timing response of 1 ms while maintaining good ACTP of less than -60 dB over the wide frequency range of 400-520 MHz.

Experimental long-term survey of mid-infrared supercontinuum source based on As2S3 suspended-core fibers

The evolution of supercontinuum generation in chalcogenide suspended-core microstructured optical fibers is studied with regard to their exposure to the room atmosphere. We report the experimental proof of aging-induced supercontinuum generation drift in chalcogenide microstructured fibers. Mid-infrared supercontinuum covering the 2.5–5.5-µm spectral region is demonstrated in a fresh and 7-month-aged counterpart As2S3 fibers, by means of a home-built multistage oscillator power amplifier delivering 300 fs pulses at a repetition rate of 43 MHz in the 3.0–4.1-µm range. Numerical simulations based on the generalized nonlinear Schrodinger equation confirm the significant alteration of supercontinuum generation due to increasing fundamental OH and SH absorption bands.

A 2-<formula formulatype="inline"><tex Notation="TeX">$\mu{\hbox{m}}$</tex></formula> InGaP/GaAs Class-J Power Amplifier for Multi-Band LTE Achieving 35.8-dB Gain, 40.5% to 55.8% PAE and 28-dBm Linear Output Power

This paper describes the first linear multistage class-J power amplifier (PA) fabricated in a 2- μm InGaP/GaAs HBT process for multi-band long-term evolution (LTE) applications. It includes a three-stage topology composed by a pre-driver, driver, and a class-J main stage, to optimize the output power and power-added efficiency (PAE) over 1.7-2.05 GHz, thus encapsulating the LTE bands 1 to 4, 9 to 10, 33 to 37, and 39. This is achieved through a novel analog pre-distorter linearizer, which features two sub-circuits for AM-AM and AM-PM linearization. The PA prototype meets the standard's adjacent channel leakage ratio at a maximum linear output power of 28 dBm. Tested at 2.05 GHz and for a 16-QAM scheme, the maximum error vector magnitude is 3.38% at a 28-dBm output power, which corresponds to a PAE of 40.5%-55.8% across bands. The input return loss is 15 dB and the maximum power gain is 35.8 dB, while demonstrating an unconditional stable characteristic from dc up to 5 GHz. The die area is 950 μm×900 μm. The performance metrics compare favorably with the state-of-the-art.

High-Efficiency Cellular Power Amplifiers Based on a Modified LDMOS Process on Bulk Silicon and Silicon-On-Insulator Substrates With Integrated Power Management Circuitry

An RF high-voltage CMOS technology is presented for cost-effective monolithic integration of cellular RF transmit functions. The technology integrates a modified LDMOS RF power transistor capable of nearly comparable linear and saturated RF power characteristics to GaAs solutions at cellular frequency bands. Measured results for multistage cellular power amplifier (PA) designs processed on bulk-Si and silicon-on-insulator on high-resistivity Si substrates (1 kΩ·cm ) are presented. The low-band multistage PA achieves greater than 60% power-added efficiency (PAE) with more than 35.5-dBm output power. The high-band PA achieves 45%-53% PAE across the band with greater than 33.4-dBm output power. Measured linearity performance is presented using an EDGE modulation source. A dc/dc buck converter was also integrated in the PA die as the power management circuitry. Measured results for the output power, PAE, and spurious emissions in the receive band while the dc/dc converter is biasing the PA and running at different modes are reported.

Efficient multi-stage load modulation radio frequency power amplifier for green radio frequency front end

The road towards the reduction in the carbon footprint associated with power-hungry wireless communication devices will require a holistic design approach to ensure that energy saving can be achieved throughout the entire system. The information and communication technology today accounted for 3 and 2% global power consumption and global CO2 emissions, respectively, where a significant portion is a result of the power consumption in the radio frequency (RF) power amplifier device. Moreover, tomorrow amplifiers will need to be reconfigurable and host a plethora of modulated signals to support effective signal processing. Therefore performance metrics such as linearity, power efficiency and their trade-off should be at the forefront of the RF power amplifier design. This study proposes an energy-efficient power amplifier design based on the Doherty configuration as part of a green RF front end for mobile WiMAX. The authors extend the classical Doherty to incorporate a three-stage load modulation design with a proposed new output power combiner. The performance of the three-stage load modulation RF power amplifier is compared with the legacy two-stage load modulation technique. The experimental results show that 30 dBm output power can be achieved with 67% power-added efficiency, which represents a 14% improvement over the current state-of-the-art system while meeting the power output requirements for mobile WiMAX.

ESD sensitivity of a GaAs MMIC microwave power amplifier

The EOS/ESD sensitivity of the main circuit blocks of a complete GaAs multi-stage power amplifier for microwave applications was investigated under HBM, MM and TLP regimes. Hard breakdown failure modes were identified due to passive components failure. The high current injection state of active components was also analyzed.

Influence of fusion splice on high power ytterbium-doped fiber laser with master oscillator multi-stage power amplifiers structure

We have developed models to investigate the power properties of monolithic fiber laser with master oscillator multi-stage power amplifiers configuration. In the simulation the effect of optical characteristics of fiber fusion splice was considered, which was introduced by connecting fiber amplifiers. The theoretical modeling was established based on the classic theory of rate equations and the computational method was described in detail. On the basis of three high-power fiber lasers with different structures, we analyzed the splice loss and return loss, and how they influence the distribution of laser power in the system. The results showed that, on the present splicing level, both the enhancement of the pump capacity of fiber laser and the reduction of the quantity of power amplifier modules were effective strategies to accomplish fiber laser with tens of thousands of watts output.

高功率单频线偏振掺镱全光纤放大器

We report an all-fiber high power, single frequency large-mode area (LMA) linearly polarized ytterbiumdoped fiber amplifiers (YDFA) module, which is based on the master oscillator multi-stage power amplifiers (MOPA). The maximum output power is 43.8 W at a wavelength of 1064 nm when 60-W launched pump light is coupled, with high slope efficiency of 88%, polarization extinction rate (PER) >17.2 dB and nearly diffraction-limited beam quality (M2<1.1).

End-pumped 300 W continuous-wave ytterbium-doped all-fiber laser with master oscillator multi-stage power amplifiers configuration

An end-pumped ytterbium-doped all-fiber laser with 300 W output in continuous regime was reported, which was based on master oscillator multi-stage power amplifiers configuration. Monolithic fiber laser system consisted of an oscillator stage and two amplifier stages. Total optical-optical efficiency of monolithic fiber laser was approximately 65%, corresponding to 462 W of pump power coupled into laser system. We proposed a new method to connect power amplifier stage, which was crucial for the application of end-pumped combiner in high power MOPAs all-fiber laser.

Analysis and design of a high-efficiency multistage Doherty power amplifier for wireless communications

A comprehensive analysis of a multistage Doherty amplifier, which can be used to achieve higher efficiency at a lower output power level compared to the classical Doherty amplifier, is presented. Generalized design equations that explain the operation of a three-stage Doherty amplifier, which can be easily extended to an N-stage Doherty amplifier, are derived. In addition, the optimum device periphery, which minimizes AM-AM distortion for perfect Doherty amplifier operation, is analyzed. For the first time, a multistage Doherty power amplifier that meets wide-band code-division multiple-access (WCDMA) requirements is demonstrated. The designed power amplifier exhibits a power-added efficiency (PAE) of 42% at 6-dB output power backoff and 27% at 12-dB output power backoff. These PAEs are more than 2/spl times/ and 7/spl times/ better, respectively, than that of a single-stage linear power amplifier at the same output power backoff levels. The power amplifier is capable of delivering up to 33 dBm of output power, and has a maximum adjacent channel power leakage ratio of -35 and -47 dBc at 5- and 10-MHz offset, respectively. To the best of the authors' knowledge, these represent the best reported results of a Doherty amplifier for WCDMA application in the 1.95-GHz band to date.

Detecting and avoiding odd-mode parametric oscillations in microwave power amplifiers

Multistage power amplifiers are prone to parametric oscillations of an odd-mode nature. In this article, a technique for detecting and avoiding odd-mode parametric oscillations in microwave power amplifiers under large-signal excitations is extended and improved. For that, two monolithic amplifiers, having different topology and different oscillation mode, are extensively analyzed. A previously analyzed X-band two-stage power amplifier is used as a first example. Then, the technique is applied to a novel L-band one-stage power amplifier exhibiting a different oscillation mode. The success in determining the oscillation nature of these two different examples and the strategies used for their stabilization clearly illustrate the potential of this technique to address the complex problem of parametric oscillations in microwave amplifiers. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE 15, 2005.

Low loss matching (LLM) design technique for power amplifiers

This paper describes a design methodology used for the development of multistage broadband power amplifiers. The method uses the measured small-signal S-parameters and loadpull data in association with low loss matching (LLM) design technique. The Q-point of the amplifier was selected for class-AB operation of the device in order to obtain the maximum power-added efficiency (PAE) and bandwidth. In the design optimization using loadline techniques, four sets of S-parameter data, corresponding to device low gain, high gain, low current, and high current, were used. These data files represent the possible fabrication changes and allow realization of a design more tolerant to process variations.

Multistage solid-state power amplifier design by a new alternative synthesis technique

For the first time, the numerical real-frequency technique has been applied to the design of a nonlinear power amplifier. This synthesis technique does not require any transistor model by directly using measured large-signal S-parameters of the power transistor device. The double power-frequency dependence of these S-parameters requires the use of a bidimensional interpolation (spline functions). With the Levenberg–Marquardt optimization and large-signal S-parameters, a specific CAD program optimizes the added-power in order to synthesize the matching networks of the PA. The simulated and measured results of two S-band power amplifiers validate the new synthesis approach. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 87–98, 2004.

Multistage solid-state power amplifier design by a new alternative synthesis technique

For the first time, the numerical real-frequency technique has been applied to the design of a nonlinear power amplifier. This synthesis technique does not require any transistor model by directly ...