Advances in the simulation of autonomous microwave circuits

Abstract

-Advances in the simulation of nonlinear microwave circuits of autonomous nature are presented, covering three relevant aspects: potential instability of power amplifiers under output mismatch effects, design of dual-band frequency dividers, with interest in multi-band communication systems, and oscillator phase-noise analysis. The instability under mismatch effects is predicted through the calculation of a 3-port scattering matrix, at three relevant sideband frequencies, which is obtained by linearizing the circuit about the large-signal steady-state solution. The dual-band divider is based on a parallel configuration, using two types of inductor-varactor cells, as well as a simultaneous design/optimization of two identical circuits, each operating at one of the two frequency bands. Finally, a new phase-noise analysis method able to predict the near-carrier spectral density in the presence of near-critical poles is described.

Analysis of Output Loading Effects in Autonomous Circuits

“…Analytical studies, such as those in [16], [21]- [22], are very insightful, but assume a small variation of the output load, so that the oscillator total admittance or impedance function can be linearized with respect to this load. This paper extends the work in [8] with a detailed investigation of mismatch effects in autonomous circuits. Unlike previous works, the new simulation method considers all possible variations of the passive output load, covering the entire Smith chart.…”

“…1(a)], where it is connected to the antenna [8]- [11]. The PA will behave nonlinearly with respect to the input source, this resulting in a certain spectrum at kfin, where k is an integer.…”

“…The PA will behave nonlinearly with respect to the input source, this resulting in a certain spectrum at kfin, where k is an integer. To analyze the possible instability under mismatch effects, a small perturbation at the frequency f [6], [8]- [11] must also be considered. In fact, the stability analysis is a prediction of the circuit reaction to small perturbations coming from noise or fluctuations.…”

“…Unless a specific design criterion is used, PA manufacturers cannot guarantee stable behavior for all the possible termination impedances. In view of this need, in [8]- [11], a potential instability analysis is addressed, taking into account that the PA termination impedances are unknown, unlike the case of standard stability analyses [12]- [14], in which all the circuit elements and parameters are specified. It is a largesignal stability analysis, so the PA input frequency fin, as well as an incommensurable perturbation frequency f must be considered.…”

“…However, the PA output network will exhibit filtering effects [8]- [11], so only the termination impedances at fin and two or three sideband frequencies (depending on the filtering characteristic) will have an impact on the stability properties. The potential instability analysis in [8]- [11] is based on the definition of a low-order outer-tier scattering matrix at the relevant sideband frequencies, calculated with the conversion-matrix approach. This enables the evaluation of several large-signal equivalents of the µ factor [15].…”