Olivier Llopis

Noise in AlGaAs/InGaAs/GaAs pseudomorphic HEMTs from 10 Hz to 18 GHz

Noise properties of AlGaAs/InGaAs/GaAs pseudomorphic HEMTs (PHEMTs) have been investigated simultaneously in the low and intermediate frequency range (10 Hz to 150 MHz) and in the microwave range (4 to 18 GHz) and compared to the noise of more classical devices such as MESFETs and GaAlAs/GaAs HEMTs. Unlike the other commercially available devices, PHEMTs exhibit the unique capability of providing simultaneously state-of-the-art microwave noise performance and a reasonable low-frequency excess noise. >

A study of the correlation between high-frequency noise and phase noise in low-noise silicon-based transistors

The evidence of a predominant contribution of the transistor high-frequency noise in residual phase-noise data is demonstrated. This behavior is observed in devices in which the low-frequency noise contribution has been carefully minimized through an optimized bias network, and at offsets frequency above 10 kHz. The phase-noise behavior is then described through nonlinear noise-figure measurements. These results open the way to phase-noise minimization, with a different approach from the one used in most circuit design tools.

On the simulation of low-frequency noise upconversion in InGaP/GaAs HBTs

Residual phase-noise measurements of GaAs heterojunction bipolar transistors (HBTs) with different low-frequency noise properties are used to investigate how accurate a compact HBT model can predict the upconversion of low-frequency noise under nonlinear operation. We find that the traditional low-frequency source implementation, as well as a cyclostationary noise source implementation, have shortcomings under different operation conditions. While, in general, the cyclostationary approach yields much better results, it fails under certain operation conditions. Experimental evidence is given that this is caused by overestimated correlation between baseband noise and RF noise sidebands. It is shown that a model based on cyclostationary sources with reduced cross-correlation yields good agreement between measurement and simulation in all cases.

Phase noise measurement of a narrow linewidth CW laser using delay line approaches.

Two different laser phase noise measurement techniques are compared. One of these two techniques is based on a conventional and low-cost delay line system, which is usually set up for the linewidth measurement of semiconductor lasers. The results obtained with both techniques on a high-spectral-purity laser agree well and confirm the interest of the low-cost technique. Moreover, an extraction of the laser linewidth using computer-aided design tools is performed.

Optimization of an ultra low-phase noise sapphire-SiGe HBT oscillator using nonlinear CAD

In this paper, the electrical and noise performances of a 0.8 /spl mu/m silicon germanium (SiGe) transistor optimized for the design of low phase-noise circuits are described. A nonlinear model developed for the transistor and its use for the design of a low-phase noise C band sapphire resonator oscillator are also reported. The best measured phase noise (at ambient temperature) is -138 dBc/Hz at 1 kHz offset from a 4.85 GHz carrier frequency, with a loaded Q/sub L/ factor of 75,000.

Analysis of noise up-conversion in microwave field-effect transistor oscillators

The conversion process of the low frequency noise into phase noise in field-effect transistors (FET) oscillators is investigated. First, an evaluation of the baseband noise contribution to the oscillator phase noise is provided from the analysis of the baseband noise and the frequency noise spectra. A distinction is made within the different components of the low frequency noise contributions to close-in carrier phase noise. Next, the frequency noise of the oscillator circuit is analyzed in terms of the FETs low frequency noise multiplied by the oscillators pushing factor. Though this product usually provides a good evaluation of the phase noise, experimental results presented here show the inaccuracy of this method at particular gate bias voltages where the pushing factor decreases to zero. To account for these observations, a new nonlinear FET model involving at least two noise sources distributed along the channel is proposed.

Phase noise in cryogenic microwave HEMT and MESFET oscillators

The influence of cooling on the phase noise of HEMT and MESFET oscillators is addressed. The initial measurements of the device DC characteristics and low-frequency noise (0.1 kHZ-100 kHz) under cooling give indications on the suitability of a given device for use in low-phase-noise cooled oscillators. Cooled pseudomorphic AlGaAs-GaInAs-GaAs HEMTs (PHEMTs) turn out to be particularly well-suited as they are free of collapse and they are free of g-r noise in the frequency range of interest. The authors report on 4 GHz oscillators operated at 110 K and featuring a phase noise below -100 dBc/Hz at 10 kHz from the carrier in spite of a very modest loaded Q

Ultra low phase noise sapphire-SiGe HBT oscillator

A state of the art C-band oscillator is presented. It is based on a high Q WGM sapphire resonator combined with a low residual phase noise SiGe HBT amplifier. A two oscillator experiment performed on this system has revealed a phase noise level of -133 dBc/Hz at 1 kHz offset from the 4.85 GHz carrier, which is the best published phase noise result for a single loop, free running microwave oscillator.

Nonlinear noise modeling of a PHEMT device through residual phase noise and low frequency noise measurements

The phase noise generated by a FET device is investigated using transmission and reflection residual phase noise measurements. This approach helps in locating, in the intrinsic device, the low frequency noise sources which are responsible for these phase fluctuations. On the basis of these experiments, a new nonlinear noise model of the FET is proposed. This model is able to describe a phenomenon that has been observed, but never modeled in the past: the dependence of the baseband noise on the microwave input power.

Analytic investigation of frequency sensitivity in microwave oscillators: Application to the computation of phase noise in a dielectric resonator oscillator

The conversion of low frequency noise into phase noise in microwave oscillators is studied through an analytical calculation of the pushing factor. This calculation is based on a simplified equivalent circuit for two types of active devices : field effect transistors (Fet) and heterojunction bipolar transistors (hbt). The preeminence in the conversion process of the gate- source capacitance in theFet and the base- emitter junction in thehbt is pointed out. Practical methods are proposed to reduce the phase noise in these circuits.RésuméLa conversion du bruit basse fréquence en bruit de phase dans les oscillateurs microondes utilisant un transistor à effet de champ (Tec) ou un transistor bipolaire est étudiée de façon analytique à partir de schémas équivalents simplifiés des composants actifs. Les expressions obtenues montrent l’ influence prédominante dans le processus de conversion des éléments du réseau d’entrée des transistors : capacité grille- source pour letec, jonction base- émetteur pour le bipolaire. Des méthodes pratiques pour la réduction du bruit de phase dans ces circuits sont proposés.