A new analytical approach in modeling of multi-loop feed-forward linearized microwave power amplifiers

Feed-forward is one of the main methods for linearization of microwave power amplifiers. Although the complexity of the system is increased, the level of inter-modulation rejection (IMR) of a feed-forward system can be improved using a multi-loop configuration. Predicting the IMR of such a system is of prime importance. A new analytical approach in modeling a multi-loop feed-forward system for predicting the linearization performance of the system is presented. The first loop of the multi-loop system is substituted by an equivalent amplifier model and then the reduced system as a new feed-forward system is evaluated. The predicted IMR values are verified using the ADS simulator and a MATLAB program.     

Computer design of broadband lumped component microwave phase shifter amplifiers

Broadband microwave phase shifts can be obtained using two amplifiers with different phase delays. A computer program which modifies circuits, by adding and removing components and nodes as necessary, has designed two amplifiers having a gain phase difference of 90 degrees but otherwise similar performance.<>     

Flexible active filter design using three-operational amplifiers

Active circuits containing three-operational amplifiers are presented from which various filter transfer functions can be easily obtained via open-circuiting appropriate passive elements. Any element value of the circuit depends only on a single coefficient of the biquadratic voltage transfer function realized.     

Analytical expressions for simplifying the design of broadband lownoise microwave transistor amplifiers

An analytical expression for the minimum achievable noise figure for a specified gain at a given frequency is derived for a microwave amplifier. The minimum noise figure is given in terms of the specified gain, the amplifier noise parameters, and the S-parameters. Similarly, another expression for the maximum gain at a specified noise figure is derived in terms of the noise figure, the noise parameters, and the S-parameters. It is shown that these expressions simplify the tradeoff considerations for broadband low noise amplifier design by avoiding the need to draw several constant noise and gain circles at each frequency of interest     

Optimized design of GaAs FET's for low-noise microwave amplifiers

In order to optimize the performance of GaAs Schottky-barrier gate FET's for small-signal amplification at a given microwave frequency, a design procedure has been established on the basis of simple analytical theories of the junction-gate FET. The design goal is to simultaneously satisfy the specifications of quantities for which there are trade-off's. These are the power gain, noise figure, and input reflection coefficient in 50-ohm lines, which represent major figure-of-merits for amplifying devices. An equivalent circuit model is constructed to include intrinsic small-signal elements calculated from the theory of Lehovec and Zuleeg, and noise current sources from van der Ziel's theory. Parasitic elements are also taken into account to reflect the state-of-the-art processing and packaging techniques. A simple, systematic method for analysing a complicated equivalent network including noise sources is devised and applied in computations. Three major design parameters of the Schottky-barrier FET, i.e. gate length, channel thickness and channel doping density are taken as independent variables in order to obtain the optimized design. An experiment is carried out to prove the validity of this theory. It is found that the theory predicts the optimized device performance with sufficient accuracy, and gives a set of optimum design parameters to a good approximation. The optimized unit, with a gate length of 1·5 μm, shows a unilateral gain as high as 21·5 dB, an F_min as low as 2·6 dB, and an input reflection coefficient around 0·85 at 4 GHz.     

Hybrid integrated lumped-element microwave amplifiers

This paper describes the development of microwave lumped-element thin-film amplifiers. The basic design philosophy underlying lumped inductors and capacitors at microwave frequencies is reviewed, showing how Q's of 100 are achieved. A variety of tunable input, output, and interstage integrated lumped-element networks for transistor amplifiers were fabricated. The gain and efficiency of 2-GHz class-C operated transistors mounted in these circuits were comparable with the best performance achieved by the same transistors in less lossy coaxial circuits. The measured losses (1.2 dB) at 2 GHz were very close to those calculated using the design parameters. Single-stage amplifiers at 2 GHz achieved one watt of output power with 4 dB of gain. At somewhat lower power levels more than 6 dB of gain was achieved. The circuits allowed the operation of low-power level class-A amplifiers with over 13 dB of gain. Cascaded operation yielded more than 17 dB of gain with 0.8 watts of CW power. It is concluded that lumped elements can be fabricated by thin-film technology and will play an important role in microwave integrated circuits.     

Velocity tapering in microwave amplifiers

The low-to-moderate RF conversion efficiencies characteristic of kinetic energy conversion devices may be enhanced by appropriately tapering the RF circuit phase velocity. The nonlinear interaction equations have been solved in closed form for an HKB (hard-kernel-bunch) model to obtain an optimum taper form. Several velocity taper forms have been investigated in experimental amplifiers and the power output, gain, efficiency, and phase shift characteristics of these amplifiers are discussed in detail. Conversion efficiencies up to 50 percent and near constant output power for a 20-dB variation in RF drive power have been realized in near optimally tapered circuit amplifiers. Further improvements realized include operation at a single voltage for maximum gain and power output and a nearly linear phase shift characteristic for a ±10 percent voltage modulation.     

Computer aided design of wide-band integrated microwave transistor amplifiers on high dielectric substrates

The problem of wide bandwidth and flat in-band gain response for microwave transistor amplifiers has been reduced to the optimization of a number of important variables from computer prepared design charts. Through the general flexibility of the computer-generated data, a large variety of amplifier responses are possible - using distributed circuit matching networks. As experimental verification of the overall design procedure, single-stage and two-stage octave wide transistor amplifiers were fabricated on 1 inch by 1 inch and 1 inch by ½ inch 20 mil thick alumina, respectively. The experimental data gained from these units showed excellent correlation with the computer predicted response.     

Closed-loop stability analysis of microwave amplifiers

A stability analysis technique of microwave amplifiers, valid for large- or small-signal regimes, is presented. The technique calculates the system poles and zeroes from a closed-loop frequency response of the circuit linearised around its steady state. The method has been applied to an S-band monolithic amplifier, detecting spurious oscillations for certain specific bias conditions and input power levels, in good agreement with measurements     

Synthesis of broadband microwave transistor amplifiers

The design of broadband microwave transistor amplifiers is discussed in terms of direct synthesis of distributed commensurate matching networks. Examples are given for both single-stage and 2-stage amplifiers, using ladder networks realisable in stripline form.     

Phase characteristics of microwave avalanche-diode amplifiers

The phase and gain characteristics of wideband, coaxial X band avalanche-diode amplifiers have been determined, and typical data are presented for an 11 GHz amplifier. At a gain of 15 dB, the phase linearity was less than 4°, the a.m.-p.m. conversion was less than 8 deg/dB and the phase sensitivity to current was about 0.2 deg/mA.     

Analysis of microwave MESFET power amplifiers for digital wireless communications systems

The analysis of microwave MESFET power amplifiers (PAs) for digital wireless communications by using the hybrid Volterra-series method is presented in this paper. Compared with the traditional approach in the pure frequency-domain operation, the hybrid method has the advantage of fast computation for the continuous spectral signals with the same accuracy. The major modification is the equivalent baseband formulations in the time domain for the digital modulation signal, and the frequency-domain treatment with the nonlinear system via Volterra-series expansion. The MESFET two-dimensional current model is utilized and detailed current expressions are given to account for the gate-drain cross-term effects, while the nonlinear capacitors are also considered to describe the MESFET nonlinear characteristics completely. Circuit-level simulation yields the output modulation signal parameters with the measured data confirmation. System performance degradations due to nonlinear distortions of the MESFET PA are also performed for the communication link with the additive white Gaussian noise channel model. These results would be very useful in PA designs for digital wireless communications systems.     

On numerical design technique of wideband microwave amplifiers based on GaN small-signal device model

This work presents an application of Normalized Gain Function (NGF) method to the design of linear wideband microwave amplifiers based on small-signal model of a device. NGF has been originally developed to be used together with an S-parameter (*.s2p) file, whereas this work enables the NGF to be able to work with explicit S-parameter formulae derived from the small-signal model of the device. This approach provides the designer to be able to use simple set of S-parameter equations instead of S-parameter file of the device. Representation of the device simply by several model equations not only eliminates the need of carrying large number of data but also provides the capability of equation-based easy, realistic and equispaced S-parameter data generation in any desired resolution in frequency axis without requiring interpolation. NGF is defined as the ratio of T and |S₂₁|², i.e. T_N = T/|S₂₁|², gain function of the amplifier to be designed and transistor forward gain function, respectively. Synthesis of output/input matching networks (OMN/IMN) of the amplifier requires two target gain functions in terms of T_N, to be used in two sequential non-linear optimization procedures, respectively. An amplifier with a flat gain of ~10 dB operating in 0.8–2.35 GHz is designed using a small-signal model of an experimental GaN-HEMT. Theoretical amplifier performance obtained in Matlab is shown to be in excellent agreement with the simulated performance in MWO (Microwave Office, AWR Inc.). A prototype low-power amplifier having a ~10 to 12 dB gain, operating in (0.9–1.5 GHz) is also produced and measured which yielded good performance results.     

Analysis and design of the true piecewise approximation logarithmic amplifiers

This paper describes the theory of operation, mathematical analysis, modeling and circuit design of the true piecewise approximation logarithmic amplifiers. These logarithmic amplifiers can be realized by the series linear limit and parallel summation methods. Both of these methods are discussed in this paper and their transfer functions are extracted. In addition, making use of the proposed formulas, a new mathematical approach is proposed for improving the characteristics of the parallel summation method. All of the presented methods are modeled in Simulink. Moreover, they are designed in a 0.13 μm CMOS technology and simulated by HSPICE. It is observed that analytical results comply with the simulation results. Considering the dynamic range, power, and area, the parallel summation method shows better performance than its series linear limit counterpart.     

Transverse-wave tubes as high-efficiency microwave amplifiers

The theory of microwave tubes using cyclotron- and synchronous-wave interactions is reviewed, and an analysis is presented of the energy exchange mechanism and the axial-beam velocity spread induced by the RF interactions in transverse-wave traveling-wave tubes. The analysis of the energy spread in a realistic model of the beam shows that the maximum efficiency attainable (with collector depression) is limited by the nonzero size of the beam and the nonzero space-charge density. Considering practical limitations of the beam parameters and the saturation characteristics, possible design parameters for high-efficiency, transverse-wave tubes operating at moderate power levels have been obtained. The attainment of such goals with reasonable circuit length appears possible but difficult, mainly due to relatively low interaction impedance available for transverse-wave interactions.     

Power amplifiers and transmitters for RF and microwave

The generation of RF/microwave power is required not only in wireless communications, but also in applications such as jamming, imaging, RF heating, and miniature dc/dc converters. Each application has its own unique requirements for frequency, bandwidth, load, power, efficiency, linearity, and cost. RF power is generated by a wide variety of techniques, implementations, and active devices. Power amplifiers are incorporated into transmitters in a similarly wide variety of architectures, including linear, Kalm, envelope tracking, outphasing, and Doherty. Linearity can be improved through techniques such as feedback, feedforward, and predistortion     

Low-frequency limitations of ultrabroadband matched microwave amplifiers

The low-frequency analysis of different structures of ultra-broadband matched amplifiers is presented. The results show clearly that the device transconductance is the most important characteristic to consider when selecting the best amplifier configuration. A new configuration is proposed.     

Characterization of a low-noise linearized microwave power amplifier module

An X-band, low-noise, linearized microwave power amplifier module consisting of a low-noise solid-state amplifier (SSA), predistortion linearizing circuit, and low-gain helix traveling wave tube (TWT) is designed and tested in order to demonstrate both reduced noise figure and suppressed intermodulation distortion ratio. Two-tone intermodulation distortion (IMD) ratios are predicted from simulations obtained from modeling of the TWT, linearizing circuit, and SSA by the use of Agilent's Advanced Design System simulation code. Simulated IMD ratios are in good agreement with measured results. Measurements show a noise figure of 2.2 dB at 9.5 GHz and the third-order IMD ratio of -53 dBc at 10 dB input back off from the input P1dB point. It is found that both noise figure and IMD ratio are significantly improved compared with conventional helix-TWTs and microwave power modules.     

Integrated circuit design for physical unclonable function using differential amplifiers

A physical unclonable function (PUF) based on process variations on silicon wafers is a very promising technology which finds various applications in identification and authentication, but only a few integrated circuits have been reported so far. As those circuits are vulnerable to power supply noises, switching noises and environmental variations, they lead to a reliability issue such as time-varying or metastable responses. To resolve this issue, this letter proposes a new integrated circuit design for PUFs using differential amplifiers. The feasibility of the proposed circuit has been theoretically analyzed and validated through HSPICE simulations for the previous and proposed circuits.