Jean-Christophe Nallatamby

A unified approach for the linear and nonlinear stability analysis of microwave circuits using commercially available tools

For the first time, an exhaustive linear and nonlinear stability analysis of multi-transistor MMIC circuits is presented. A key point of the proposed stability analysis lies in that it can be easily implemented on any CAD package. Our straightforward and powerful approach allows both linear and nonlinear stability analysis of any complex circuit submitted or not to large RF signals. Following our novel approach, a MMIC HBT power amplifier was analyzed. Division frequency phenomena and spurious oscillations were detected by simulations and confirmed by measurements.

A general program for steady state, stability, and FM noise analysis of microwave oscillators

Two novel algorithms are presented for nonlinear autonomous circuit CAD. In the first, a symbolic simulator is used to calculated the possible oscillation frequencies of the circuit, and the high-level behavior of the oscillator is determined by the harmonic balance method extended to autonomous circuits. The second algorithm is based on the conversion matrix method, which allows simulation of nonlinear microwave oscillator phase and amplitude noise spectra with linear and nonlinear correlated noise sources.<<ETX>>

Phase noise in oscillators - Leeson formula revisited

In the field of linear feedback-systems formalism, the Leeson formula is a useful tool for the determination of phase noise in feedback oscillators. Nevertheless, a direct application of the Leeson model without care can lead to erroneous results because the formula contains hidden parameters that are generally unwittingly ill evaluated or neglected. Thus, a brute-force calculation of phase noise with the Leeson formula can lead to errors of several orders of magnitude (i.e., several tens of decibels). A detailed analysis enables us to enlighten the hidden parameters leading to a modified Leeson formula that is valid for all oscillator circuits. It explicitly takes into account all the parameters needed for phase-noise calculation. In order to demonstrate the ease of use and accuracy of the new formula, we apply it to several oscillator circuits with lumped elements, transmission lines, and high-Q resonators. Finally the analytical results are confirmed by numerical simulations with a nonlinear transistor model.

An advanced low-frequency noise model of GaInP-GaAs HBT for accurate prediction of phase noise in oscillators

We present a new low-frequency noise model of a GaInP-GaAs HBT and the associated extraction process from measurements. Specific measurements enable us to locate the two dominant low-frequency noise sources. Their spectral densities extraction as a function of the emitter bias current is then performed and a normalized scalable model is deduced. The cyclostationarity of the low-frequency noise sources is justified. The whole noise model including the shot noise source is implemented in the nonlinear HBT model used in the United Monolithic Semiconductors foundry. In order to verify the validity of the scalable noise model, several voltage-controlled oscillators with different center frequencies and tuning bandwidth have been designed and processed. Comparisons between the predicted performances and experimental results show an excellent agreement and validate the proposed low-frequency noise modeling of multifinger HBTs.

Amplitude and phase noise of magnetic tunnel junction oscillators

The microwave emission linewidth of spin transfer torque nano-oscillators is closely related to their phase and amplitude noise that can be extracted from the magnetoresistive voltage signal V(t) using single shot time domain techniques. Here we report on phase and amplitude noise studies for MgO based magnetic tunnel junction oscillators. The analysis of the power spectral densities allows one to separate the linear and nonlinear contributions to the phase noise, the nonlinear contribution being due to the coupling between phase and amplitude. The coupling strength as well as the amplitude relaxation rate can be directly extracted.

Low-Frequency Noise Measurements of Bipolar Devices Under High DC Current Density: Whether Transimpedance or Voltage Amplifiers

Different setups for the measurement of the low-frequency noise of semiconductor devices have been proposed in the literature, based on the use of either low-noise voltage amplifiers (VAs) or, more recently, transimpedance amplifiers (TAs). This paper aims to address the applicability and physical limit of each configuration, when they are applied to measure the LF noise of HBTs or diodes at moderate to high DC current densities. Extracted noise curves issued from different setups are analyzed. Noise data collected from recent low-noise technologies shows that physical limits are being systematically approached

On the role of the additive and converted noise in the generation of phase noise in nonlinear oscillators

In a conventional approach, the oscillator phase noise due to noise sources near carrier is defined as additive phase noise by assuming that the oscillator operates in a near linear fashion. Nevertheless, fundamentally, an oscillator circuit is inherently nonlinear. In this paper, we show that the phase noise generated by noise sources around the fundamental frequency of oscillation is due to two simultaneous and correlated phenomena of the same order of magnitude: additive phase noise and converted phase noise due to conversion from one sideband to another. An analytical calculation applied to a simple purely theoretical circuit allows evaluation of the respective influence of the two above-mentioned phenomena. Numerical simulations performed on a realistic transistor oscillator circuit then confirms the importance of the conversion phenomenon already shown by the analytical evaluation. The converted noise results to be of the order of 6 dB higher than the additive noise. The term of additive phase noise must be intended to characterize the phase noise generated in linear components located out of the nonlinear oscillation loop and, for example, in buffer amplifiers following the oscillator itself.

A new method for the design of ultra low noise oscillators

We describe a newly developed design method of free running oscillator circuits leading to the minimum phase noise, for given transistor and resonator. This method has allowed us to design a 9.2 GHz oscillator using a PHEMT transistor and a sapphire resonator stabilized at 330 K, presenting a measured phase noise of -80 dBc/Hz at 100 Hz offset from carrier with an 1/f/sup 3/ slope. This result represents the state of the art of HEMT free running oscillators at room temperature.

Stability Analysis of Millimeter-Wave Circuits. Application to DC-40GHz PHEMT amplifier and Ku-band HBT power amplifier

Specific CAD oriented methods have been developed [1] for linear and non-linear stability analysis. Both methods are applied to multi-transistor MMIC circuits. These approaches can be easily implemented on any CAD packages and enable linear and non-linear stability to be analysed with a localization of instability paths within an N-transistor circuit. Simulations and measurements of two MMIC circuits (DC-40GHz PHEMT amplifier for optical links and Ku-band HBT power amplifier) demonstrate the efficiency of the proposed methods during the MMIC design processs.

Accurate design of HBT VCOs with flicker noise up-conversion minimization, using an advanced low-frequency cyclostationary noise model

We present a scalable cyclostationary low frequency noise model of GaInP/GaAs HBT, oriented to oscillator circuits CAD, and its implementation in commercial simulators. In order to verify the validity of the scalable noise model, several MMIC VCOs have been designed in the microwave range from 2GHz up to 24 GHz and processed at UMS foundry. Experimental results have been compared with the predicted one showing an excellent agreement without any retrofitting. They validate the proposed low frequency noise model for multifinger HBTs. To our knowledge it is the first time that VCOs are designed using non linear transistor models including LF cyclostationary noise sources.