Jacques Graffeuil

Evaluation of noise parameter extraction methods

The influence of the algorithm used for noise parameter fitting on the accuracy of the microwave noise parameter measurements is investigated. Five different commonly used algorithms are compared by a statistical analysis including instrument accuracy specifications. Some of these algorithms are found to be more efficient in terms of available accuracy and computer time. The best predicted available accuracies reported betwen 4 and 20 GHz for each noise parameter compare well with observed accuracies on noise parameter measurements performed with a dedicated test set on a noise standard made of a passive two-port. The accuracy on minimum noise figure is found to be 0.1 dB maximum. >

Noise modeling of microwave heterojunction bipolar transistors

Analytical expressions of microwave heterojunction bipolar transistors minimum noise figure and noise parameter are reported in this paper. These expressions are derived from a noise model including nonideal junctions, emitter and base resistances and have been compared with measured data obtained on a Si-SiGe HBT. An agreement between theoretical and experimental data was as observed up to 20 GHz for several bias conditions. The limits of the model or the range of validity of the proposed equations have been also examined with the help of an appropriate CAD software. The analysis of the influence of parasitic elements on noise parameters has shown a strong influence of the extrinsic base collector capacitance at microwave frequencies. >

Small-signal and noise model extraction technique for heterojunction bipolar transistor at microwave frequencies

The increasing use of Heterojunction Bipolar Transistors (HBTs) in microwave analog circuits requires a valid description of these devices by means of an equivalent circuit including noise sources in an extended bias and frequency range. This paper describes a technique to extract the elements of the equivalent circuit from simultaneous noise and S-parameter measurements. Additionally, the conventional high frequency bipolar junction transistor (BJT) noise model is shown to work well with HBTs. Recent results obtained from GaInP/GaAs HBTs are reported. >

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. >

Influence of surface recombination on the burn-in effect in microwave GaInP/GaAs HBT's

In this paper, we report on the early increase of the dc current gain (burn-in effect) due to the electrical stress of carbon doped GaInP/GaAs heterojunction bipolar transistors (HBTs). Devices featuring different passivation layers, base doping, and emitter widths were investigated. The obtained data demonstrate that the burn-in effect is due to a reduction of the surface recombination located at the extrinsic base surface, around the emitter perimeter. It is concluded that the recombination centers are related to defects at the passivation/semiconductor interface and that, during the stress, they are passivated by hydrogen atoms released from C-H complexes.

A 6-GHz Low-Power BiCMOS SiGe:C 0.25

A 6-GHz low power SiGe direct digital synthesizer (DDS) is reported. This letter discusses the BiCMOS design improvements used for the phase accumulator and the phase-to-amplitude conversion in order to achieve higher speed operation and lower power consumption compared to existing DDS. The phase accumulator is based on a three-level BiCMOS logic, and the phase-to-amplitude conversion is completed through a bipolar differential pair. The circuit has been processed in a BiCMOS SiGe:C 0.25 mum technology. The power consumption is 308 mW and it operates from a 2.8 V supply. The chip core area is 1 mm2.

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An experimental setup, based on current/voltage conversion through transimpedance amplifiers (TAs), has been implemented for the direct full low-frequency noise (LFN) characterization of Si/SiGe heterojunction bipolar transistors (HBTs) in terms of base and collector short-circuit current noise sources. This setup performs a full characterization, as it measures simultaneously the two noise current sources and their correlation, thanks to an original technique based on the specific properties of a specially designed buffer amplifier using a low-noise common-base bipolar transistor (CB BJT). By means of translation formulae, the obtained measurements are compared with those carried out with a multi-impedance technique. They show a good agreement both for the noise sources spectral densities and for their correlation. The TA-based setup provides enhanced capabilities in terms of measurement speed and remote control potentialities.

m Direct Digital Synthesizer

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.

Transimpedance amplifier-based full low-frequency noise characterization setup for Si/SiGe HBTs

We report here on low-frequency (LF) noise of GaAs/ GaAlAs TEGFETs. Present investigations show that this noise is not inherently lower in TEGFETs than in MESFETs. Moreover, the bias and frequency dependence of the noise was found to indicate that traps in GaAlAs have a fundamental influence on LF noise. A close correlation is subsequently observed between the noise level at ambient temperature and the TEGFET static and dynamic performances at low temperature (130 K).

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

The first characterization of the low-frequency noise in a self-aligned Si/SiGe heterojunction bipolar transistor (HBT) is reported. The observed low-frequency noise exhibits a pure 1/f shape, probably related to carrier number fluctuations at the pseudomorphic emitter-base heterointerface.<<ETX>>