High gain millimetric negative resistance low noise amplifiers

The limited gain available from GaAs FETs and HEMTs at millimetric frequencies can be overcome by using the devices in a negative resistance amplifier configuration. The advantage of the solid-state negative resistance amplifier over the transmission amplifier is that the gain available is not limited by the active device used. It has been shown that, over a narrow bandwidth, significantly higher gain can be obtained from a negative resistance amplifier, when compared to a transmission amplifier using the same device, while maintaining the same overall noise performance. This has been demonstrated experimentally using a 0.25 mu m HEMT device.<>     

Phase mismatch in traveling-wave parametric amplifiers

A misunderstanding is corrected regarding the effect of phase mismatch on the gain in traveling-wave parametric amplifiers. It is shown that gains greater than unity can be obtained even when the signal and idler waves do not grow exponentially.     

Four-wave mixing in traveling-wave semiconductor amplifiers

The traveling-wave equations of four-wave mixing in semiconductor amplifiers are solved analytically including saturation of the amplifier. Excellent agreement is obtained with numerical solutions of the traveling-wave equations. The analytical model is used to analyze a highly nondegenerate four-wave mixing experiment in a bulk semiconductor amplifier     

Performance degradations of multigigabit-per-second NRZ/RZlightwave systems due to gain saturation in traveling-wave semiconductoroptical amplifiers

A nonlinear model for a travelling-wave semiconductor optical amplifier has been used to determine eye closure degradations for 2.4 and 10 Gb/s NRZ/RZ lightwave systems due to gain saturation effects in the optical amplifier. At 10 Gb/s, with a carrier lifetime of 300 ps, the results indicate that the penalty is less than 1 dB for both NRZ and RZ systems provided that the ratio of the input power (P_in ) to the saturation output power (P_sat) is less than -17 dB. The NRZ system penalty is slightly larger than the RZ penalty when P_in/P_sat is larger than -17 dB. For example, with P_in/P_sat=-10 dB, the NRZ system penalty is about 2.8 dB versus 2 dB for the RZ system. The system penalty at 2.4 Gb/s is slightly less than that at 10 Gb/s. At P _in/P_sat=-10 dB, the NRZ system penalty is about 2.5 dB versus 1.5 dB for RZ     

General design procedure for high-efficiency traveling-wave amplifiers

A general design procedure is developed for the design of both low-power and high-power high-efficiency traveling-wave amplifiers. The process is based on the selection of optimum values (for highest efficiency) of the design parameters C, QC, B and b from the large-signal curves and design of an amplifier with the particular type of RF structure specified by power and bandwidth requirements and operating parameters as near the optimum values as possible. In cases where the optimum design parameters cannot all be realized simultaneously, the design engineer will be able to select the parameter that he wishes to adjust. The procedure is first developed for helix-type tubes and then correction factors are derived that permit the design of amplifiers with any type of RF structure from the same set of curves.     

Four-wave mixing in traveling-wave semiconductor laser amplifiers

Nondegenerate four-wave mixing (NDFWM) effects on simultaneous amplification of copropagating and counterpropagating waves with a frequency spacing of a few gigahertz in a 1.5-μm nonresonant near traveling-wave semiconductor laser amplifier are discussed. Experimental results are in qualitative agreement with a theoretical model assuming the NDFWM process is mainly due to carrier pulsation produced by the beating of copropagating waves in the amplifier. The amplification of a phase-modulated wave is considered. Time-reversal properties of four-wave mixing are demonstrated     

Gain saturation in traveling-wave semiconductor optical amplifiers

The gain saturation behavior of semiconductor traveling-wave optical amplifiers has been analyzed using a model that includes the specific dependence of gain on carrier concentration. Under the condition of a specific gain at a particular current, it is found that the saturation power strongly depends on the choice between quantum well (QW) or bulk amplifying medium but weakly on the detailed design of the device such as the number of QW's or the thickness of the bulk layer. The higher saturation power of the QW-based amplifier is caused by its logarithmic gain-current relation rather than its low optical confinement factor. Also, when the unsaturated device gain is specified, the designed saturation power can be obtained with the lowest drive current by using the highest optical confinement     

Photon point process for traveling-wave laser amplifiers

The authors determine the evolution of the photon point process of a light beam as it passes through a traveling-wave laser amplifier (TWA). In particular, when coherent light is presented to the input of the amplifier, the output photon statistics are characterized by a marked-Poisson (MP) point process, which has a noncentral-negative-binomial (NNB) output photon-number distribution (PND). Using this distribution we calculate the probability of error (PE) for an ON-OFF keying (OOK) direct-detection photon-counting communication system, and show that the results differ somewhat from those obtained when the Gaussian-PND approximation is used. It is shown that receiver performance is optimized by filtering the amplifier output. Analysis of the point process is of interest because it permits the time response of the amplifier to be determined; this, in turn, allows the effects of intersymbol interference to be calculated     

Design and analysis of novel high-gain and broad-band GaAs pHEMT MMIC distributed amplifiers with traveling-wave gain stages

Using the concept of traveling-wave gain stages, novel GaAs pseudomorphic high electron-mobility transistor monolithic-microwave integrated-circuit (MMIC) distributed amplifiers (DAs) are demonstrated to achieve high gain and over several octaves of bandwidth performance simultaneously for microwave and millimeter-wave frequency applications. The cascaded single-stage distributed amplifier (CSSDA) is used as traveling-wave gain stages to improve the gain performance of the conventional distributed amplifier (CDA). By adopting the low-pass filter topology between the CDA and CSSDA and tuning the gain shape of CDA and CSSDA separately, a broad-band and high-gain DA, called CDA-CSSDA-2, was accomplished. The detailed design equations are derived for the broad-band matching design of this CDA-CSSDA-2. Two other MMICs, namely, a two-stage CSSDA called 2-CSSDA, and another two-stage design called CDA-CSSDA-1, are also included in this paper. This CDA-CSSDA-2 achieves 22/spl plusmn/1.5-dB small-signal gain from 0.1 to 40 GHz with a chip size of 1.5/spl times/2 mm/sup 2/. It also produces a gain-bandwidth product of 503 GHz, which is the highest among all reported GaAs-based DAs. The flat group delay also demonstrates the feasibility of this design for future digital optical communications and broad-band pulse applications.     

Large signal behavior of high power traveling-wave amplifiers

The results of an experimental investigation on the large signal behavior of a kilowatt power level helix type traveling-wave amplifier tube are presented. Operation with and without attenuators was investigated using a movable electromagnetic probe to measure power level along the tube. Quite different effects of drive power and beam voltage on the saturation level were found for operation with and without attenuators. The maximum power level is lower for attenuator operation. Also, power levels do not continue to increase with increasing beam voltage and drive power. In contrast, attenuator-less operation produces the highest efficiency, and the power levels continue to rise with increasing beam voltage and drive power. Conversion efficiencies as high as 25 per cent are obtained with an attenuator and as high as 40 per cent without an attenuator. Efficiency calculations based on small-signal theory can be made to agree reasonably well with the experimental attenuator-less operation efficiencies by assuming an appropriate ratio of the ac component of beam current to the dc component of beam current, i/I0.     

Theoretical power output and bandwidth of traveling-wave amplifiers

Expressions are developed to calculate the theoretical power output of traveling-wave amplifiers using any type of RF structure. Calculations are made for helix-type tubes and it is shown how to calculate the power output of tubes using more dispersive structures in terms of calculations made for helix tubes. The principal factors accounting for higher power output of dispersive structures are presented and discussed. The gain and bandwidth of forward-wave helix amplifiers are derived from the small-signal theory as functions of frequency and it is shown that the gain in db times the frequency bandwidth is a constant as a function of helix length for highgamma_{0}a'and the gain times the bandwidth squared is a constant for lowgamma_{0}a'.     

Applications of traveling-wave laser amplifiers in subcarriermultiplexed lightwave systems

Describes applications of traveling-wave laser amplifiers (TWLAs) in subcarrier-multiplexed distribution systems for both frequency-modulated (FM) and amplitude-modulated vestigial-sideband (AM-VSB) video signal distribution. The characteristics of a 1300-nm facet-angled and antireflection-coated TWLA are described. Analytical carrier-to-noise ratio (CNR) characterizations of subcarrier-multiplexed systems employing TWLAs are given. Experimental results of using TWLAs in multichannel FM and AM-VSB video signal systems are described. The potential optical-reflection problems associated with the residual reflectivities of optical fiber connectors and splices while using TWLAs are briefly described     

Gain saturation in traveling-wave ridge waveguide semiconductor laser amplifiers

The saturation behavior of traveling-wave ridge waveguide diode amplifiers is studied both numerically and analytically. It is shown that an 'effective saturation power' can be used to characterize the saturation of these devices by up to 4 dB. The effective saturation power, which is sensitive to device geometry, carrier density, and operating wavelength, is useful in the design of the ridge waveguide optical amplifiers.<>     

A note on gyrotron traveling-wave amplifiers using rectangular waveguides

The coupling constant ε between a relativistic electron beam and the TE10rectangular waveguide mode is calculated. By reducing the height of the waveguide, this coupling constant may exceed the corresponding value for the operation with the TE11circular polarized mode, under identical conditions of the electron beam. The calculation is followed by a discussion on optimum mode choice in gyro-TWA's.     

Fully printed electronics on flexible substrates: High gain amplifiers and DAC

We propose a novel simple Fully-Additive printing process, involving only depositions, for realizing printed electronics circuits/systems on flexible plastic films. This process is Green (non-corrosive chemicals), On-Demand (quick-to-print), Scalable (large-format printing) and Low-Cost vis-à-vis Subtractive printing, a complex deposition-cum-etching process that otherwise requires expensive/sophisticated specialized IC-like facilities and is Un-Green, Not-On-Demand, Un-scalable and High-Cost. The proposed Fully-Additive process features printed transistors with high (∼1.5 cm²/Vs) semiconductor carrier-mobility, ∼3× higher than competing state-of-the-art Fully-Additive processes and comparable to Subtractive processes. Furthermore, passive elements including capacitors, resistors, and inductors, and two metal-interconnect layers are likewise Fully-Additive printed–to our knowledge, to-date the only Fully-Additive process capable of realizing complex circuits/systems on flexible plastic films.Several analog and mixed-signal circuits are demonstrated, including proposed and conventional differential amplifiers, and a charge-redistribution 4-bit digital-to-analog converter (DAC). The proposed amplifier embodies a novel positive-cum-negative feedback to simultaneously significantly improve the gain and reduce susceptibility to process variations. To improve the speed and reduce the area of the DAC, the parasitic capacitors therein are exploited. The Fully-Additive proposed amplifier and DAC are benchmarked against reported realizations (all Subtractive-based processes), and are shown to be highly competitive despite its realization based on the simple low-cost proposed Fully-Additive process.     

Efficiency of broadband four-wave mixing wavelength conversionusing semiconductor traveling-wave amplifiers

We present a theoretical analysis and experimental measurements of broadband optical wavelength conversion by four-wave mixing in semiconductor traveling-wave amplifiers. In the theoretical analysis, we obtain an analytical expression for the conversion efficiency. In the experiments, both up and down-conversion efficiencies are measured as a function of wavelength shift for shifts up to 27 nm. The experimental data are well explained by the theoretical calculation. The observed higher conversion efficiency for wavelength down-conversion is believed to be caused by phase interferences that exist between various mechanisms contributing to the four-wave mixing process     

Loop gain measurement in feedback amplifiers

This paper presents a method of loop gain measurement for DC-coupled feedback amplifiers, which overcomes the short-comings of some earlier well-known methods. The method discussed in this paper is similar in principle to one presented by Middle-brook (1975), but has the advantage that the instrumentation which is required for its successful application is much simpler, This method can be applied fairly routinely to measure loop gain accurately.     

Current gain high-frequency CMOS operational amplifiers

The performance of high unity gain-bandwidth current gain-based CMOS operational amplifiers fabricated in a 1.5-/spl mu/m CMOS digital process is discussed. High unity-gain bandwidth was achieved by using short-channel MOS transistors operating in the current gain mode. Stacked current mirrors have been utilized as current gain stages to minimize the effects of the channel-length modulation in short-channel MOS transistors. Open-circuit gain of 60 to 70 dB, a unity-gain bandwidth of 70 to 100 MHz, and slew-rate of 200 V//spl mu/s were demonstrated at a DC power dissipation of 1-2 mW.     

Limits on amplification of picosecond pulses by using semiconductorlaser traveling-wave amplifiers

The limiting factors in picosecond pulse amplification by semiconductor traveling-wave laser amplifiers are investigated, including the effects of the spontaneous emission. For the amplifier with a negligible amount of spontaneous emission, amplification is limited by the energy saturation for low-repetition-rate pulses, while the power saturation is the limiting factor for high-repetition-rate pulses. The spontaneous emission decreases both the signal gain of the amplifier and the signal-to-noise ratio considerably. The effective gain recovery time and the effective saturation energy are strong functions of the input pulse energy, and the amount of the spontaneous emission