Michel Prigent

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.

High efficiency free running class F oscillator

A free running 1.6 GHz oscillator yielding 67% power efficiency with 24 dBm output power is proposed. It is based on the use of a transistor working in the an high efficiency class F associated to an appropriate feedback network. The transistor is a 2 mm gate periphery, 0.7 /spl mu/m gate length MESFET built by the Thomson foundry. The main impact of the characteristics of the constitutive components on the overall oscillator performance is also discussed.<<ETX>>

A unified approach of PM noise calculation in large RF multitone autonomous circuits

This paper presents a simulation method to compute noise in autonomous and forced circuits using the harmonic balance (HB) formulation. Thanks to iterative linear solvers and multi-dimension conversion matrices, it can handle large multi-tone circuits to calculate phase noise spectra near and far from the carrier frequency. Its efficiency is illustrated with two real circuits.

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 distributed, measurement based, nonlinear model of FETs for high frequencies applications

For the first time, a FET nonlinear model, distributed along the gate length and extracted from pulsed I(V) and pulsed S-parameters measurements is presented. This model has led to a better prediction of power saturation mechanism and offers promising perspectives for intermodulation and nonlinear noise modeling at high microwave frequencies.

On the determination of the thermal impedance of microwave bipolar transistors

This paper has two main axis: firstly, we address the experimental characterization of the frequency-dependent thermal impedance of microwave bipolar transistors from continuous wave (CW)-only measurements (both DC and AC). From the experimental perspective, we will review some of the already available methods and propose a new method based on a recent observation. It will be shown that under proper measurement control, a reasonable precision of the computed value can be achieved. The method is applied to characterize the global (external) behavior of a multi-finger Heterojunction Bipolar Transistor (HBT), whose physical structure is known. A distributed thermal circuit, entirely derived from 3D thermal simulations, is incorporated into a complete distributed electrothermal model of the device, whose global behavior is validated by measurements. Then from a distributed electrothermal simulation perspective, we will address the power and temperature distribution between fingers as a function of the power dissipated by the device, and will show that the global behavior in measurements is close to the worst case in terms of highest temperature among individual fingers.

Efficient algorithm for steady-state stability analysis of large analog/RF circuits

This paper presents a method for the investigation of AC and large signal steady-state stability of electrical (analog/RF) circuits. In both cases stability/instability are detected through fast calculation and analysis of circuit poles. Thanks to iterative algorithms (Krylov-subspace methods) applied to modified nodal formulation of conversion matrices, a selection of poles is computed, allowing the method to be applied to large size circuits of any type of topology.

On the cyclostationary properties of the 1/f noise of microwave semiconductor devices

This paper addresses, from an experimental perspective, the long-standing question on whether the 1/f noise of microwave semiconductor devices should be considered cyclostationary in compact models. By using a simple instrumentation setup and basic mixer concepts, it will be shown that the external equivalent current noise sources of such devices simply CANNOT be stationary. To demonstrate our ideas, a through experimental analysis was carried out on purely-resistive bridge circuits made up of microwave varactors and transistors under large-signal operation whose DC current component is kept constant. When computing the voltage noise power of specific circuit arrangements, errors in excess of 20dB may be induced if the stationary concept is adopted. The difference between the stationary or cyclostationary concepts will be simulated with the aid of the simulator ADS from Agilent.