Low-noise room-temperature parametric amplifier

The use of the phase-locked degenerate parametric amplifier in digitally modulated communication systems has been proposed. In the letter, we report successful operation of this device as an amplifier for high-speed phase-shift-keyed signals. Noise temperature measured on a 4 GHz device by a system (error-rate) measurement and by a Y factor method give a noise temperature of 46 K, including 11 deg K from the circulator, with the amplifier at room temperature.     

Low-noise wideband indium-phosphide transferred-electron amplifiers

X band pulsed, InP transferred-electron reflection amplifiers have been characterised by a study of the small-signal admittance, the large-signal dynamic conductance and the noise figure. These measurements have been made as functions of voltage, frequency and temperature on a number of different vapour epitaxial layers. The lowest observed noise figure was 8.8 dB at 10.0 GHz. An instantaneous bandwidth of more than 4 GHz at 7 dB gain has been obtained using a simple impedance-equalisation circuit.     

Low-noise parametric amplifiers tunable over one full octave

Various possible ways of tuning low noise coolable parametric amplifiers through a full octave without adjusting the pump frequency are analyzed. Based upon this analysis, a novel and simple method is proposed and practically verified. In agreement with the theory, noise temperatures between 100/spl deg/K (at 4 GHz) and 240/spl deg/K (at 8 GHz) were achieved in a balance C-band amplifier.     

Low-noise klystron amplifiers

The principles of low-noise guns have been applied to klystron amplifiers with good corroboration of the theory. In the past, many people thought that klystrons had inherently high noise figures, while others advanced the theory that low-noise guns might be used with klystrons as well as with wave tubes. The development to be described here shows that the former impression is not true and verifies that low-noise klystron amplifiers are possible. The most obvious difference between the guns for low-noise klystron amplifiers and those typical of low-noise traveling-wave tubes is the higher beam current which is required for adequate klystron gain. A byproduct of this higher current is a wide dynamic range. In addition to the development of the electrical parameters, a major effort went into klystron construction techniques somewhat peculiar to low-noise klystron amplifiers. The data taken show that alignment of the low-noise gun electrodes with the drift tube, alignment of the beam with the magnetic field, elimination of the collector's secondary electrons from the beam, and cleanliness of the tube are of primary importance in constructing a low-noise klystron amplifier. Several two-cavity, low-noise klystron amplifiers were built for operation in both S-band and C-band. The typical low-level gain was 11.5 db, and the saturated power output was 180 mw. Several tubes exhibited noise figures below 9 db; the lowest value obtained was 6.7. db.     

Low-noise amplifiers for WCDMA base-station receivers

This paper focuses on the design and measurements of low-noise amplifiers (LNA) targeted for WCDMA base-station applications. In addition, various gain control techniques and the accuracy in noise measurements have been analyzed. Two different LNA designs are presented. Both LNAs can be operated in two gain modes, which are optimized for different base-station configurations. Both designs are implemented using the same 0.25-μm SiGe BiCMOS process, and both designs achieve the NF of 1 dB and IIP3 of ?5 dBm in high gain mode.     

Two-diode parametric amplifiers

Analysis suggests that very useful performance may be achieved in parametric amplifiers incorporating two varactor diodes. The most interesting configuration is a bandpass amplifier in which the varactors are the shunt capacitive elements, operated with a phase shift between diodes of 90° at the centre signal frequency and with the diodes mounted with opposite polarities. With inphase pumping this gives unilateral operation and a large potential bandwidth.     

Low-noise amplifiers in wireless communications: state of the art,two new wideband all-active LNAs in SiGe-BiCMOS

The aim of this paper is three-fold. First, it introduces the low-noise amplifier, its relevance in modern wireless communications receivers and the performance expected of it. Then, it presents an exhaustive review of the existing topologies, presenting their advantages and shortcomings. And finally, it introduces a new class of LNAs, based on current conveyors, describing the founding principle and the performances of two new LNAs, one single-ended and the other differential. Both these new LNAs offer the following notable advantages over existent topologies: total absence of passive elements (and the smallest LNAs in their respective classes); wideband performance, with stable frequency responses from 0 to 3 GHz; easy gain control over wide ranges (0–20 dB). Comparisons with other topologies prove that the new class of LNA implementations greatly advances the state of the art. These amplifiers are ideally suited to today’s multi-band receivers.     

Simulating parametric amplifiers

In this paper, the problems of producing a general simulator model of a parametric amplifier are discussed. This model is to be simple, accurate, and applicable to many forms of parametric amplifiers. A brief discussion of the theory behind parametric amplification is followed by proposals for three models. Each of these is discussed in terms of its limitations and applications. The results of tests on two of these models are presented, and these results are discussed. Some emphasis is placed on the most sucessful of the models, which has been used to simulate a subharmonic oscillator.     

Low-noise two-wired buffer electrodes for bioelectric amplifiers

Active buffer electrodes are known to improve the immunity of bioelectric recordings against power line interferences. A survey of published work reveals that buffer electrodes are almost exclusively designed using operational amplifiers (opamps). In this paper, we discuss the advantage of utilizing a single transistor instead. This allows for a simple electrode, which is small and requires only two wires. In addition, a single transistor adds considerably less noise when compared to an opamp with the same power consumption. We then discuss output resistance and gain as well as their respective effect on the common mode rejection ratio (CMRR). Finally, we demonstrate the use of two-wired buffer electrodes for a bioelectric amplifier.     

Intermodulation in parametric amplifiers

Third-order intermodulation products due to the charge-voltage nonlinearity of the varactor diode in a parametric amplifier have been computed. Some experimental data obtained from a two-carrier measurement have been reported. Finally, the noise power density in a telephone channel due to parametric amplifier intermodulation has been calculated as a function of total input power into the amplifier.     

Ion/electron-beam parametric amplifiers

Recent experiments with positive-ion beams suggest that an ion?electron beam, consisting of an electron beam superimposed on an ion beam, such that the two beams have different drift velocities, is realisable. A five-frequency parametric amplifier using an ion?electron beam is proposed.     

Detuning effects in parametric amplifiers

Some detuning effects in parametric amplifiers have been observed when the pump frequency is above and below the optimum value. A possible explanation of these effects is suggested.     

Gain stabilisation of parametric amplifiers

A method of stabilising the gain of a parametric amplifier from the pumped conduction current of a varactor diode is described. Long-term stabilities of 0.1dB/week have been achieved on a 13dB-gain amplifier with diode currents of less than 1 ?A.     

Subharmonic pumping of parametric amplifiers

The purpose of this paper is to present in some detail the operation of a parametric amplifier pumped subharmonically as compared to being directly pumped. As considered here, subharmonic pumping does not involve harmonic pump power generation (external to the varactor) but the utilization of higher-order time-dependent capacitances to yield parametric amplification by employing, basically, only a three-frequency system. The analysis given here is based on an evaluation of the Fourier series representation of the time-dependent capacitance resulting from large-signal ("hard") pumping of varactors. This evaluation indicates that significant values of higher-order time-dependent capacitances suitable for parametric amplification are obtained with relative pump swings in excess of about 90 per cent. Utilizing these higher-order time-dependent capacitances, the amplifier operation for various orders of subharmonic pumping is treated, including such factors as pump power requirements, gain, and noise figure. It is shown that, under certain conditions, less pump power is required to generate the same negative conductance than with direct fundamental pumping. Furthermore, for the same pump power and fundamental pump frequency, it is determined that significant improvements in amplifier noise figure are achieved by employing subharmonic pumping, provided varactor losses are small. From the results obtained by both analysis and experiment, it is concluded that subharmonic pumping, even without harmonic power generation, is not only feasible but can be very useful up to C-band signal frequencies with existing varactors.     

Nondegenerate electron beam parametric amplifiers

Cyclotron wave amplifiers with a pump-to-signal frequency ratio of 5:1 (rather than the usual 2:1) have been built and have given a single-channel noise figure of 2 db. This paper reports on the difficulties which had to be overcome and the restrictions which had to be observed before achieving what, at the start, had looked deceptively simple. The paper begins with a discussion of the relative merits of assigning signal, idler and pump waves in various ways to beam and circuit. In the preferred arrangement the circuit carries only the pump wave; signal and idler are cyclotron waves on the beam. The validity of Tien's equations for the propagation constants and of the Manley-Rowe relations for the power-frequency ratio is demonstrated for the case of cyclotron waves. It is also shown that in a nondegenerate tube, idler noise must be extracted, no matter how high the idler frequency may be. Early experiments by C. B. Crumly, using interdigital couplers for signal and idler, gave very poor noise figures. The twisted coupler, a new structure with high coupling efficiency, was introduced but failed to reduce the high noise. It was then found that a signal carried by a cyclotron wave of low phase velocity was attenuated as it traveled along the beam, and that the noise extraction process worked poorly. This was traced to the spread of axial electron velocities, a source of trouble mentioned by C. P. Lea-Wilson and later by E. I. Gordon. P.G. Everett's measurements of this effect are described. It is then shown how the consequences of the effect may be minimized. Nondegenerate tubes are described in which the velocity spread effect is rendered almost harmless. The twisted coupler structure is particularly well adapted to experiments with synchronous waves; a brief report on such experiments is included.     

Gain limitations in optical parametric amplifiers

Factors limiting the gain of parametric amplifiers pumped by the 266 nm harmonic of aQ-switched Nd:YAG laser have been investigated, and the advantages of combined parametric/dye amplifiers in the visible are discussed.     

Active reactance compensation of parametric amplifiers

The increase in bandwidth potential of a simple parametric amplifier obtained by adding active rather than passive filter elements to the signal circuit is discussed. Measured performance data of an amplifier constructed for the 4GHz satellite-communication band is given; by using this technique, a sevenfold increase in bandwidth at 20dB gain was obtained     

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.     

Backward optical parametric oscillators and amplifiers

Degenerate backward optical parametric oscillators and amplifiers have been considered, for the first time, to the best of our knowledge. When the pump intensity is four times the threshold pump intensity, the conversion efficiency reaches a maximum value. On the other hand, for nondegenerate optical parametric oscillators, the conversion efficiency always increases as the pump intensity increases. This behavior is different from those for forward optical parametric oscillators. In either configuration, the oscillation can occur without an external feedback. There is, however, a distributed feedback provided through the opposite propagation directions of the signal and idler. The threshold pump intensities for the oscillators can be achieved by the lasers currently available based on quasi-phase matching in several structures. As the input intensity for the backward parametric wave increases, the gain for this wave decreases dramatically if the pump intensity is on the order of the threshold or higher. When the input intensity is much larger than the threshold pump intensity, there is almost no gain regardless of the level of the pump intensity     

铒铥共掺碲基质宽带光纤放大器研究

文章作者分析了铒铥共掺碲基质光纤放大器在980 nm泵浦下Er~(3+)-Tm~(3+)离子之间的能量转移过程,建立了速率方程和功率传输方程,并通过仿真得出了其放大增益随光纤长度和泵浦功率的变化规律.仿真结果表明:通过优化光纤长度和泵浦功率,该放大器可以在1 440～1 540 nm波段得到高达50 dB的平坦增益.