Noise in Single-Frequlency Oscillators and Amplifiers

A generalization of previous oscillator noise analyses has been developed to permit reliable noise characterization of active nonlinear devices. Effects due to sideband correlation in the equivalent noise source are included. A rotating wave approximation (RWA) developed by Lax is used in obtaining the amplitude and phase noise spectra. Conditions are given for phase stabilization of free-running oscillators and for minimum phase noise in phase-Iocked oscillators and amplifiers. Stability criteria, discussion of spurious sidetones, and effects of a noisy synchronizing signal are given. The noise measure is used to obtain alternative expressions for the noise spectra and the carrier-to-noise ratios of locked oscillators and amplifiers. It is shown that the noise power gain of AM fluctuations is usually much lower than the corresponding gain for FM noise. The theory should be useful in optimizing the noise performance of nonlinear RF generators, such as IMPATT, BARITT, and Gunn diode oscillators.     

Noise in IMPATT Diode Amplifiers and Oscillators

The results of experimental and theoretical investigations of the noise characteristics of lMPATT diode amplifiers and oscillators are presented. The oscillator noise is shown to consist of three different contributions: modulation noise, selectively amplified primary noise, and conversion noise. The influence of the active device nonlinearity and load circuit parameters is discussed in detail. The experimental results are in good agreement with the theoretical predictions. It is especially pointed out that the large correlation between AM and FM fluctuations, usually measured in IMPATT oscillators, indicates nonoptimum AM noise performance. Experimental techniques for achieving optimum AM noise performance are demonstrated (orthogonal noise tuning). By a simple extension of the model, the noise behavior of an injection phase-locked oscillator can be described. The calculated AM and FM noise power spectra for the synchronized oscillator are also shown to be in good agreement with experimental results. Finally the signal-to-noise ratio for current modulated IMPATT oscillators is investigated and optimization is demonstrated.     

Transferred electron (Gunn) amplifiers and oscillators for microwave applications

Transferred electron amplifiers and oscillators are now well established as important members of the family of active microwave solid-state devices. The combination of power output, gain-bandwidth product, and noise figure that has been achieved with stable linear transferred electron amplifiers cannot be matched by any other type of microwave solid-state amplifier. Transferred electron oscillators have produced the highest power output obtained so far from a single solid-state device at microwave frequencies, they can be electronically and mechanically tuned over larger frequency ranges than other types of solid-state oscillators, and well designed transferred electron oscillators have exceptionally low AM and FM noise. An introductory survey of the history and the current status of the theory, technology, and application of transferred electron devices is presented. The future outlook for these devices appears bright.     

Theory of Noise and Transfer Properties of IMPATT Diode Amplifiers

A theory is formulated which describes quantitatively the noise and transfer properties of IMPATT diode reflection-type negative resistance amplifiers. This theory is based on the method used in the large-signal theory of noise in IMPATT diode oscillators by the present authors. The theory takes into account the signal dependence of the noise generation in the diode, the noise and/or modulation present in the input signal, and also the intermodulation effects occurring between the various frequency bands. The equations are conveniently arranged in matrix form; such a formulation makes it easier to obtain quantitative results in terms of measurable noise and modulation parameters. Agreement between measured and theoretically predicted AM and FM noise of injection-locked oscillators is good. The usefulness of the theory is illustrated by results of calculations on minimum attainable noise of a given amplifier, maximum noise allowable on the input signal, AM-FM conversion, phase distortion, bias modulation, and the correlation between various types of noise.     

IMPATT Pump Sideband Noise and its Effect on Parametric Amplifier Noise Temperature

This paper describes an investigation of the amplitude modulation (AM) noise sidebands of silicon IMPATT microwave oscillators and the effect these noise sidebands have on the excess noise temperature of parametric amplifiers. It is shown that the noise temperature may be affected under both large- and small-signal conditions to an extent which depends on the level of pump sideband noise. Simple relationships between easily measurable amplifier properties and pump noise power are given which enable the performance of any combination of pump and amplifier under the two signal conditions to be predicted. A method which simultaneously eliminates the small-signal effect and reduces the large-signal effect to an acceptable level is proposed and demonstrated to be a practical solution.     

Molecular amplification and generation of microwaves

This paper is a general introduction to the field of amplification and generation of microwaves using molecular rather than electronic processes. The basic physical properties of molecular systems as related to amplification are reviewed. The properties of molecular amplifiers, such as gain, bandwidth, saturation power, and noise figure are discussed and several specific types of amplifiers are described. These include the molecular-beam maser, the “hot-grid cell”, amplifiers excited by radio-frequency pulses and by “adiabatic fast passage”, and amplifiers based on multilevel molecular internal energy systems, including “optically pumped” amplifiers. Molecular amplifiers may add very little noise to the signal to be amplified: noise figures under 1 dB can be obtained. With suitable feedback, such amplifiers become oscillators of extremely high spectral purity. High gains can be achieved using regeneration, but bandwidths are relatively small. These range from the order of tens of kilocycles for amplifiers using a gaseous molecular system, to megacycles, using solids. Molecular amplifiers saturate at low input powers, of the order of microwatts. Variations of the devices discussed may provide a means of generating millimeter and submillimeter waves     

A Two-Stage IMPATT-Diode Amplifier

The system aspects and packaging of a two-stage FM IMPATT-diode amplifier are described. The amplifier combines the output power of 4 IMPATT diodes in the final stage to provide an output power of greater than 4 W at 6 GHz. The system has a locking bandwidth of greater than 200 MHz with a 16-dB gain and a noise figure of less than 50 dB. Both the design and the experimental performance of the amplifier and each of its stages are discussed. The noise characterization of IMPATT-diode amplifiers, operating as injection-locked oscillators or stable amplifiers, determined the mode of operation for each stage. Included in the paper are experimental results of large-signal noise characterization of both Si and GaAs IMPATT diodes, as are the noise characteristics related to the output power and gain.     

High-efficiency avalanche mode in microstrip

High-efficiency-mode operation of S1 avalanche diodes as pulsed oscillators and amplifiers has been observed in microstrip. Impedance and transmission-loss measurement of the circuit are presented.     

Low-noise operation of CW GaAs avalanche diode oscillators

Previous pulsed low-noise measurements of avalanche oscillators have now been extended to CW devices having GaAs vapor-grown p-n junctions. The best AM noise-to-signal ratio observed was -140 dB, which is about 15 dB better than previously measured for GaAs avalanche diode oscillators.     

Noise in avalanche transit-time devices

The work performed on noise in avalanche transit-time devices is reviewed and presented in detail. Both theoretical and experimental results on the noise mechanisms and performance of these devices when employed as oscillators, amplifiers, and self-oscillating mixers are included. Suggestions for further studies in this area are also given.     

Intrinsic AM noise in singly tuned IMPATT diode oscillators

Analytical relationships are derived for the ratio of the intrinsic AM to FM noise, and for the intrinsic AM noise of IMPATT diode oscillators. The theory is confirmed experimentally for a silicon n⁺-p diode and an n-gallium-arsenide Schottky barrier diode operating at low and intermediate signal levels.     

Experimental Evaluation of Noise Parameters in Gunn and Avalanche Oscillators

Equations are presented that express noise-to-carrier ratio and rms frequency deviation of a negative-resistance oscillator with a multiple-resonant circuit in terms of effective available noise power densities of both 1/f and white-noise sources, an effective saturation factor, and an appropriate Q/sub L/ of the oscillator. Experimental evaluation of the noise parameters in Gunn and avalanche oscillators by use of these equations is described. AM and FM noise measurements have been made on X-band Gunn oscillators and Si and GaAs avalanche oscillators for frequency off carriers extending from 1 kHz to 10 MHz. Both 1/f and white noise have been observed in these oscillators. The validity of the above equations has been verified for Gunn oscillators from the dependence of the noise spectra on Q/sub L/. For Gunn oscillators and Si and GaAs avalanche oscillators, the effective noise-temperature ratio for white noise, N/kT/sub 0/, has been found to be 23~29, 41~51, and 38~44 dB, and the effective saturation factor to be 2~2.9, 0.5~2.4, and 2, respectively. An increase of N/kT/sub 0/ with the RF voltage across the diode has been observed in Si avalanche oscillators. Parameters for 1/f noise have also been evaluated approximately.     

A theory of noise in GaAs FET microwave oscillators and its experimental verification

A theory has been developed which provides an entirely analytical approach to the calculation of AM and FM noise in free-running GaAs FET microwave oscillators. The theory is based on the model that low-frequency device noise is mixed with the carrier signal via the nonlinearity of the FET and upconverted to microwave frequencies. Because of the analytical nature of the theory, all the important device and circuit parameters on which the noise generation depends are explicitly given. Two GaAs FET oscillators have been fabricated and used to investigate the FM noise. The theory predicts well both the spectral dependence and the absolute magnitude of the FM noise in both oscillators. The noise performance of the oscillators differs by 19 dB. The theory indicates that no single factor is responsible for this, and moreover that attention should be given to the optimization of many device and circuit features in the design of a low noise FET oscillator.     

Fine Grain Spectrum Analysis of Pulsed Microwave Amplifiers

With the advent of microwave transmitter systems requiring high spectral purity, it has become important to control the interline noise and modulation products in the fine grain spectrum of CW or pulsed microwave amplifiers. Some of the causes of interline noise and modulation in high-power microwave amplifiers such as klystrons, TWT's and coaxial triodes are reviewed in this paper. A spectrum analyzer capable of resolving interline noise and modulation products in CW or pulsed microwave spectrums is described. This analyzer has a dynamic range of better than 50 db and a resolution of less than 2 cps. Some typical measurements made on transmitters operating in the UHF and L-band regions are presented.     

Noise properties of pulsed ruby laser amplifiers

The spontaneous emission noise properties of a pair of pulsed ruby laser amplifiers have been studied. Absorption and scattering loss measurements coupled with gain measurements as a function of pump time gave a measure of the inversion attained in the amplifiers. The high inversions reached enabled the authors to overcome the inherent noisiness of a 3-level system by having N2considerably larger than(m_{2}/m_{1}) N_{1}. Total spontaneous emission power was measured at gain saturation for each amplifier. Comparison of the observed with the theoretically expected spontaneous noise power gave good agreement.     

Determination of Equivalent Circuit Parameters Describing Noise from a Gunn Oscillator

The AM and FM fluctuations in an oscillator output are originated from impedance fluctuation in low frequencies (baseband noise) and voltage or current fluctuation in the vicinity of the carrier frequency (RF noise). In this paper, from newly defined "complex correlation coefficient between AM and FM noises," contributions of baseband and RF noises to the AM and FM noises are determined. Examples of data for X-band Gunn oscillators show that both the AM and FM noises are mainly caused by the baseband noise in the vicinity of the carrier frequency (within 1-kHz band), whereas they are mainly due to the RF noise at frequencies further than 10 kHz from the carrier frequency.     

Measurements of the close-to-carrier f.m. noise of pulsed InP t.e.o.s primed by an external oscillator

Experiments on phase-primed, pulsed InP transferred-electron oscillators show that the noise due to priming jitter can be reduced below the inherent noise level of the oscillator. Measurements are presented on the magnitude and spectrum of the oscillator noise.     

Characterization of ion-implanted IMPATT oscillators

Recent experimental results on impact avalanche transit-time diode oscillators fabricated by ion implantation are presented. The technique and problems involved are given. The diodes gave CW X-band power output up to 1.4 watts with efficiencies up to 8 percent. AM sideband noise measurements indicate that the load admittance for minimum noise is not coincidental with that load for maximum power output, and that a reduction of 20 dB in noise may be achieved with a reduction of only 0.5 to 3.0 dB in power output from the maximum power point by the proper choice of the load. AM sideband noise as low as 130 dB below the carrier in a 1-kHz bandwidth and at a sideband of 50 kHz from the carrier has been measured utilizing this technique.     

Noise measure of metal-semiconductor?metal Schottky-barrier microwave diodes

We calculate the impedance and noise measure of metal?semiconductor?metal (m.s.m.) microwave diodes. Assuming that the noise is caused by space-charge-smoothed shot noise accompanying the d.c. bias current, one comes to the conclusion that noise measures less than unity are possible. If shot noise is the main contributing noise source, then m.s.m. diodes should become extremely low-noise microwave oscillators and amplifiers.     

Noise in Synchronized Oscillators

Noise in synchronized oscillators is analyzed using a simple oscillator model. It is shown that the FM noise can be considerably improved by synchronization while the AM noise degrades slightly. It is also shown how the noise spectrum becomes unsymmetrical with respect to the synchronizing freqnency when it differs from the free-running frequency.