A Comparison of One- and Two-Idler Parametric Amplifiers (Correspondence)

The performance of a two-idler parametric amplifer is compared with that of a single-idler amplifer with a broad-banding resonator at its input. Both circuits contain the same varactor and are pumped at the same frequency. For most of the cases considered the two-idler amplifier gives a somewhat narrower bandwidth, slightly higher noise temperature, but lower sensitivity to variation of m/sub 1/ (the pump modulation rate) than the single-idler amplifier. The comparison is made over a range of pump and varactor cutoff frequencies     

Parametric Amplifier Noise Analysis

The effect of a different value of series resistance associated with the varactor in its imbedding at each of the important frequencies present in a one-port parametric amplifier is analyzed. The modified equations for effective noise temperature, amplifier gain and pump power required thus obtained are compared to experimental values measured on a 4.8 Gc/s parametric amplifier. Finally a simple and precise method for adjusting the amplifier to get close correlation between the measured varactor parameters using Kurokawa's method at signal idler, and pump frequencies and the overall amplifier performance is presented.     

A Balanced-Type Parametric Amplifier

A balanced-type diode amplifier is reported, in which the cutoff mode of the pumping waveguide resonating with the diode capacitances, is used as a signal circuit and a series connected diode loop is used as an idler. Theoretical noise-figure and gain-bandwidth product are derived after calculating the equivalent susceptance of two diodes which are parallel-connected for the signal input and series-connected for the idler. This reveals that 1) the noise figure of the balanced-type amplifier can be expressed in the same form as that of the single diode amplifier, and 2) the gain-bandwidth product is identical to that of the single diode amplifier. In the experiment at 1900 Mc, a bandwidth of more than 200 Mc is obtained at the gain of more than 10 db. A single-channel noise-figure of 2.5 db is measured at the pump power of 100 Mw.     

Spreading Resistance as a Function of Frequency

The equivalent circuit applicable to most semiconductor diodes contains a term R/sub s/ called the spreading resistance which is a very critical parameter of any diode. In a mixer diode, R/sub s/ limits the conversion efficiency and increases the noise temperature. In parametric amplifiers, R/sub s/ affects the overall impedance levels and determines the minimum noise figure of which the amplifier is capable. In harmonic generators it drastically affects the conversion efficiency, as it dissipates power not only at the input and output harmonic frequencies but also at every idler frequency for which current may flow through the diode. This paper details more specifically the problems encountered when high frequency operation must be evaluated. The cylindrical capacitor is examined with emphasis on the configuration which applies to the variable-capacitor diode, which is used primarily for harmonic power generation. The point-contact diode configuration is examined and the field equations are derived in terms of the oblate spheroidal coordinates. It is shown that this is the natural coordinate system for such an analysis and that the spreading resistance is quite easily derived in this system.     

Noise characteristics of fiber optical parametric amplifiers

We derive an analytical theory for the noise figure of an undepleted and lossless fiber optical parametric amplifier (FOPA). Both the signal and the wavelength converted idler are investigated. Our theory is applicable for both an ideal pump power source, as well as a noisy one. We find that a noisy pump source can severely degrade the performance at high gain due to the stochastic gain-variations the signal and idler will experience. The theory is compared with Monte Carlo simulations of the FOPA and an excellent agreement is obtained. Simulations in the gain-depleted region show the possibility to reach below quantum-limited, phase-insensitive amplification for single channel transmission.     

Theoretical analysis for low-noise beam transducers

Analytical expressions for the noise figure of a traveling-wave amplifier (TWA) preceded by a nonuniform drift space are derived. Numerical results show that the noise figure for an accelerated beam has a minimum at a specific drift length. Also, when the noise figure is plotted as a function of heater power, it shows a minimum value.     

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     

Stabilization of the Gain versus Frequency Characteristics of Parametric Amplifiers at High Input Signal Levels

Decreasing the negative bias voltage of varactor diodes in a parametric amplifier causes the gain versus frequency characteristic of the amplifier to shift to the higher-frequency side, resulting in a so-called "positive slope" at the signal center frequency. The same happens when the pump power is increased or when the signal power is increased, but in the latter case only when the idler circuit load resistance is below a certain value. The slope of the gain characteristic can be partially or completely compensated by detuning the signal-circuit characteristic relative to the gain versus freqnency characteristic in such a way that the latter is located on a certain point of the left or right slope of the signal-circuit chara-teristic, or by resistive loading of the idler circuit. Complete cancellation was achieved in the range from -30 to -20 dBm signal input power by using both methods simultaneously on a practical model of a parametric amplifier operating at a signal center frequency of 3.95 GHz and a pump frequency of 11.76 GHz. The loading of the idler circuit was done by drawing a little rectified diode current. The necessary increase in pump power, in order to maintain the same gain as with both signal and idler circuits tuned to resonance, was less than 3 dB, the increase in noise figure a few tenths of 1 dB from a typical value of approximately 3 dB.     

On Noise in Distributed Amplifiers at Microwave Frequencies

Formulas for the noise figure, and the minimum noise figure of a multi-link distributed amplifier have been developed. In addition, a relatively simple approximation formula has been devised that predicts the minimum noise figure of a practical amplifier design with good accuracy up to frequencies of 9 GHz. Finally, after the dependence of the noise characteristics on the circuit parameters is discussed, the noise figures of a 2--18-GHz three-link module are computed and compared with those measured on an actual amplifier. The measured data across the 2--18-GHz band compare favorably with the computed results. Measurements and theory agree that only small improvements in noise figure may he achieved, when noise matching the module's input impedance.     

复杂条件下分布光纤拉曼放大器噪声特性的解析表达式

在同时考虑抽运光和信号光之间不同偏振态、多波长抽运以及抽运光和信号光损耗系数不同的情况下 ,导出了分布光纤拉曼放大器 (DFRA)的等效噪声系数解析公式 ,并据此定量研究了抽运光和信号光之间的偏振关系对DFRA特性的影响以及DFRA与掺铒光纤放大器 (EDFA)级联时系统光信噪比 (OSNR)的改善ΔOSNR。指出 :随着DFRA开关增益的增加 ,ΔOSNR会由线性增加逐渐变为对数增加而趋于饱和。解析结果与已发表文献的数值模拟结果基本吻合     

Proposal of low-noise amplifier utilizing resonant tunnelingtransistors

A low-noise amplifier utilizing the negative input resistance of resonant tunneling transistors (RTT's) is proposed. Expected features of the RTT amplifiers are: 1) negligible effect of noise sources at the output, owing to their large power gain; 2) flat variation of noise figure (NF) versus frequency, due to white spectra of noise sources at the input; and 3) a high maximum oscillation frequency (f_max) (over several 100 GHz), Based on simulated DC characteristics, over 500 GHz f_max and 0.3 dB NF at 100 GHz are predicted for optimized AlGaAs/GaAs/AlGaAs resonant tunneling diodes (RTD's). In an RTT formed by coupling an FET to an optimized RTD, 0.55 dB minimum noise figure and 26 dB associated gain are predicted at 100 GHz. Also, a 1/w² spectrum of the input noise resistance is predicted at low frequencies     

Notes on a Crystal Mixer Performance

A simple relation between optimum rf source impedance for minimum noise figure and the nominal conversion loss of a mixer is derived. This impedance is related to the input mismatch and its dependence on the type of IF amplifier input circuit is discussed. Relations between the crystal noise temperature and mixer noise temperature as a function of conversion loss are derived for different load conditions at the image frequency terminals.     

Optimization of pump and signal powers for wavelength converters based on FWM in semiconductor optical amplifiers

We investigate the effect of input pump and signal powers on the noise performance and intersymbol interference (ISI) in a frequency-converter based on four-wave mixing (FWM) in a semiconductor optical amplifier. We demonstrate that there is an input pump power at which the noise figure of the frequency converter is a minimum, and a corresponding input signal power for which the output signal-to-noise ratio (SNR) is a maximum. We report bit-error-rate measurements which show that there is a trade-off between maximizing the output SNR, and minimizing intersymbol interference in the SOA. Consequently, the power penalty incurred in the frequency conversion can be minimized by careful selection of the input signal power. We show that power penalties of less than 1 dB are achievable.     

Super low noise C-band PHEMT MMIC low noise amplifier with minimuminput matching network

A two-stage PHEMT MMIC low noise amplifier with a very low noise figure as low as 0.76 dB and gain >16 dB at 5.4 GHz has been implemented using a minimum input matching network. It is believed that the noise figure of 0.76 dB is the best result ever reported to date from MMIC LNAs over this frequency range. This is attributed to the low noise performance of the PHEMT transistor and minimised parasitic resistance of the input matching network     

CMOS低噪声放大器的噪声系数优化

目前大量的研究文献已经描述了如何找到使噪声系数最小的低噪声放大器输入网络的最佳品质因数,但是它们往往遗漏了一个重要的参数——源极电感负反馈低噪声放大器中的栅极电感,它的寄生阻抗为低噪声放大器增加了明显的噪声。本研究课题提出了2种优化方法,这2种方法均满足功率匹配并均衡了晶体管所产生的噪声贡献和栅极寄生阻抗所产生的噪声贡献,从而实现了在栅极电感品质因数、功耗、增益限制下的噪声优化。     

Minimum Noise Figure of Paramps with F2 Frequency Dependent Apparent R/sub s/ (Correspondence)

The effect of inverse-squared frequency dependence of the apparent resistance of varactor diodes is discussed in the optimization of the noise figure of negative resistance and up-converter parametric amplifiers. Optimum idler frequency for a given signal frequency for minimum noise figure is calculated. It is also shown that about twofold improvement in the noise figure is obtained if the proper idler frequency is used for negative resistance amplifiers. It is also shown that the value of the optimum loading changes for upconverter amplifiers.     

Low-frequency reactance amplifier

A reactance amplifier has been constructed which is capable of low-noise amplification at audio and subaudio frequencies [1]. Stable voltage amplification of 20-30 db and noise figures as low as 0.16 db (50-K source resistance) have been observed for signal frequencies between 2 and 50 cps. The circuit configuration is a double sideband up-converter or modulator in which a band of frequencies from dc to several hundred cycles is used to modulate a 150-kc carrier. An analysis for noise and gain is presented which considers the average, fundamental, and second-harmonic components of the time-varying diode capacitance. The amplifier input is a signal at low audio frequency, while the output is composed of the sum and difference sidebands of the pump. Gain is realized through up-converter action associated with the frequency shift from signal frequency to near pump frequency; the sum and difference sidebands are further amplified in the output tank by the negative resistance resulting from the action of the component of time-varying capacitance at the second harmonic of the pump frequency. Gain and equivalent input noise resistance are discussed as functions of detuning in the passive output tank; measured and calculated results are compared. A scheme is also presented for stabilizing the amplifier at high values of negative resistance gain.     

Impact of pump OSNR on noise figure for fiber-optical parametric amplifiers

Electrical measurements of the noise figure of a fiber-optical parametric amplifier are presented and compared with optical measurements. The transfer of pump noise by four-wave mixing was clearly demonstrated. A numerical model was developed to simulate the transfer of pump noise and validated by these measurements. Using this model, we determine, for practical systems, a minimum required pump optical signal-to-noise ratio of 65 dB.     

Traveling-wave tube analysis of the Adler tube

The cyclotron waves on an electron beam in the pump field of the Adler tube are studied with respect to their circular polarization. It is found that positive and negative circularly polarized beam waves are coupled through the pump electric field. As a consequence of the coupling, the small signal traveling-wave analysis leads to the conclusion that the positive circularly polarized beam wave is comprised of the fast signal wave and all idlers of frequenciesn(omega pm omega_{p})where n is an even integer, while the negative circularly polarized wave is comprised of all idlers with odd integral values of n. This information appears to be new, and can perhaps be used to design input and output couplers which discriminate against unwanted idler waves.     

在瑞利散射影响下分布拉曼光纤放大器噪声特性的解析解和参数优化

光纤中的瑞利散射会对分布拉曼光纤放大器的噪声特性产生不利影响。通过忽略高次瑞利后向反射的影响,给出实际情况下(信号损耗不等于抽运损耗,考虑瑞利散射影响)分布拉曼光纤放大器噪声特性的解析解。利用此解析解,对分布拉曼光纤放大器的噪声特性进行了深入讨论并提出了选择抽运功率的一般原则