Capturing asymmetrical spectral regrowth in RF systems using a multislice behavioral model and enhanced envelop transient analysis

Abstract

Nonlinear distortion in RF and microwave systems results in spectral regrowth of digitally modulated signals. The distortion above and below the main channel can be at different levels and this is attributed to baseband effects. This article presents a new multislice behavioral-model architecture that captures this asymmetry and can be implemented in a variety of circuit simulators, including SPICE, harmonic balance (HB), envelope transient (ET), and system simulators. The work is experimentally validated using an HBT power amplifier at 2.5 GHz driven by a WCDMA signal. The model is used with envelope transient circuit simulation which is enhanced to accommodate an arbitrary baseband transfer function.

A low-order nonlinear amplifier model with distributed delay terms

“…There are models presented in the literature that use several tens of terms in the power series representation. For example, Jang used a 17th-order polynomial to get an acceptable error [22]. Nonetheless, it is observed and introduced in the following sections that the proposed model in this paper can achieve acceptable accuracy with much less order of the power series.…”

“…Although the phase error seems high with respect to the total change in the phase, this much error can be acceptable for the fundamental tone. If the polynomial order increases too much, for example, the 17th-order, as Jang [22] did, the phase error could diminish, and then the model becomes more complicated. The model phase error would increase with the decreasing order of the polynomial order.…”

“…There are models presented in the literature that use several tens of terms in the power series representation. For example, Jang used a 17th-order polynomial to get an acceptable error [22].…”

Behavioural modelling of amplifier asymmetry in the time domain

“…At the end of the simulation, the result is scaled back up to the original RF. Section presents a modified version of the basic multi‐slice model along with details of the extraction procedure for its constituent blocks. This model is employed in the time‐domain using carrier downconversion, transient simulation and finally carrier upconversion.…”