Investigation of power amplifier performance under load mismatch conditions

Abstract

The time-varying loading conditions that power amplifiers (PAs) experience in active antenna systems degrade their overall performance. Consequently, the design of linear and highly-efficient PAs under mismatch is more important than ever. In this paper, different common and promising PA architectures, i.e. class-B, balanced, Doherty (DPA) and load-modulated-poweramplifier (LMBA), are analyzed under mismatch. Their sensitivity in terms of linearity, efficiency and output power is compared under a LTE signal excitation. Average drain efficiency (DE), average output power, normalized-mean-square-error (NMSE) as well as maximum output power variations are presented for each architecture as function of the voltage-standing-waveratio (VSWR). Thereby, the most suitable PA architecture to be integrated in active antenna systems may be identified.

Theoretical Comparison of Different Envelope Elimination and Restoration Transmitter PWM Modulator Configurations to Expand the Possible Antenna Mismatch

“…This expression confirms the independence of the VSWR value at the edges of the signal band from the value of the operating frequency obtained as a result of modeling. The dependence of the VSWR on the bandwidth calculated in accordance with (11) for the frequency band of the useful signal coincides with the simulation results shown in Figure 16.…”

“…Currently, there are more than 220 entries in the IEEE Xplore digital library alone corresponding to a search for "envelope elimination and restoration". At the same time, in Powerful RF path operating features [10], including for a mismatched load [11], have been considered in sufficient detail. A number of studies on the features of EER transmitter operation with a mismatched load [12], including a narrow-band (NB) load [13,14], have revealed very stringent requirements for the allowable antenna parameters.…”

“…When the HF stage in the EEP PA operates in a switching mode, it practically represents a "short circuit" between the HF load and the output of the envelope amplifier in the low-frequency region. Also, unlike the ET PA, any envelope path mismatch is Powerful RF path operating features [10], including for a mismatched load [11], have been considered in sufficient detail. A number of studies on the features of EER transmitter operation with a mismatched load [12], including a narrow-band (NB) load [13,14], have revealed very stringent requirements for the allowable antenna parameters.…”

Mitigation of Load Mismatch Effects Using an Orthogonal Load Modulated Balanced Amplifier

“…The effect of mismatch in different class-E PA implementations was studied in detail in [3], while the works in [4]- [6] focused on the effect in Doherty PAs, and [7] on an envelope-tracked PA. In [8], [9], different PA architectures have been compared in terms of sensitivity to load mismatch, showing the advantage of using balanced PAs, which is the focus of the simplified study in [10]. In general, there is an agreement that load mismatch leads to degradation of output power, efficiency and linearity; this can be reflected in a change of behavioural model coefficients representing the PA [11] based on the load.…”

Quasi-Load Insensitive Doherty PA Using Supply Voltage and Input Excitation Adaptation

“…Although many of the described techniques are effective and have been proven for single-ended PAs, in modern telecommunication applications dealing with high peak-to-average power ratio (PAPR) signals, this should be extended to PAs based on topologies with high BO efficiency, such as the Doherty or Outphasing PAs. In fact, the performance degradation and, consequently, the expected correction also depends on the considered PA topology [12], so the following approaches are focused on reducing the performance degradation due to load variations on PA topologies with higher BO efficiency.…”