Clipping the drain bias can help achieve higher average efficiency without generating nonlinear distortion from clipping the envelope of the RF signal at the drain. That is why two different drain trackers were constructed. Following envelope power instead of envelope amplitude and varying also the input bias makes DB substantially different from envelope tracking ET. Summary drops in average power gain. In any case, a fifth order approximation results in an non-negligible error in the estimation of C0.
Let the input envelope amplitude of the single-tone gate voltage i. Optimization theory applied to dynamic biasing distortion. Kocer Middle East Technical University. The conclusion from the literature is that carefully designed drain modulation can positively impact efficiency, linearity and gain. A point-search algorithm to find a biasing path 11 10 Gain dB 9 Min 3rd H. The Agilent NA differential probe was used to measure the voltage drop across the resistor. That is due to the large gain drops at low input power levels for this GaN transistor when biased statically in deep class AB or class B mode.
In Chapter 4 the biasing functions were expressed as first and second order polynomials of input power, for the drain and gate, respectively, and the coefficients were found using random search optimization.
It is then that clipping the drain bias waveform comes in handy, since ACPR3 for ET with drain bias clipping becomes lower than that of the static bias case both for fixed and dynamic gate biasing andrespectively.
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Case 1 is the reference. It is relatively flat in gain ;ower phase-shift: The simulated results in Figure 5. On the other hand, an exact scaled replica of the envelope is fed into the bias of the switching amplifier, so that the output contains both phase and envelope information.
The roll- off factor of the RRC filter is 0. Unfortunately, some internal parameters of the transistor, such as the drain-source capacitance, are sensitive to bias variations, especially to the gate ,.
Random search is again used to solve the optimization problems, ampliffier the bias functions are once again formulated as polynomial functions of the input power see 4.
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AET varies the drain bias voltage—as in envelope tracking ET —, but the fundamental difference between conventional ET and AET is the mechanism of generating the drain modulated bias signals. G, VD clipped In ET, the amplification of both DC and AC components of the bias signal is handled by the envelope amplifier, or amplfier unit. There are nonetheless certain issues that must be dealt with carefully when manipulating the bias. The drain bias voltage varies from 2 V to 10 V for all curves.
In this case DB acts more as a linearization mechanism than as an efficiency enhancement method.
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In practice, depending on the optimization problem and on the error function, it might be unlikely that the global optimum is found.
The chapter begins by explaining the automated measurement setup, and the modifications to the optimization method from Chapter 4. Therefore, efficiency in back-off can be enhanced by varying the drain bias voltage according to the envelope power of the input signal .
HBT transistor at More than symbols were simulated. Using a first-order polynomial for the drain has the advantage that that the drain bias bandwidth is only twice the RF bandwidth, in this case 54 Mmmic. These measures have a simple structure and take into account poer phase of the nonlin- ear distortion coefficients. The list of input and output variables, the parameters, and a detailed description of the algorithm used is given in Appendix B.
Measurement of different device technologies Table 5. This last point is important because gain drops with the input power should be avoided, else a buffer amplifier would have to be added before the PA to obtain the same output power.
Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal’s published version of the work e. System composed of a digital predistorter followed by a power am- plifier modeled as a 5th order memoryless complex polynomial. When EL was derived in Section 4. As explained in Section 4.
Nevertheless, since no carrier frequency is considered in the expression, it would not contain any harmonic components of the first or second tones. Finally, the PAs used in the system must be able to cope with variable resistive load impedances.
ampilfier The capability of handling higher breakdown voltages and providing high current density makes GaN specially suited for high power applications.
They can be roughly classified into two main categories: The results for single-tone characterization shown in figures 4. If the peak output voltage is 28 V, however, the minimum output voltage will then be 8 V Table 5. The dynamic bias sources Building a highly efficient wide bandwidth bias source is a subject of current research, as it is a complex task, and is out of the scope of this work. In order to shift the Scontours diagonally upwards, one can design the matching for a lower bias point as shown in Figure 3.