Efficiency Optimization for Burst-Mode Multilevel Radio Frequency Transmitters
- Mon, Apr 01, 2013
The utilization of a burst-mode PA together with pulse-width modulation (PWM) is a promising concept for achieving high efficiency in radio frequency (RF) transmitters. Nevertheless, such a transmitter requires bandpass filtering to suppress side-band spectral components to retrieve the wanted signal, which reduces the transmit power and the transmitter efficiency. To boost efficiency for signals with high PAPRs and signals at variable transmit power levels, burst-mode multilevel transmitters have been widely discussed as a potential solution.
This work describes an efficiency optimization procedure of burst-mode multilevel transmitters for signals with high PAPRs and signals at variable transmit power levels. The impact of the threshold value on the transmitter efficiency is studied, where the optimum threshold value and the maximum transmitter efficiency can be obtained according to input magnitude statistics. Simulations are used to validate the efficiency improvement of the optimized burst-mode multilevel transmitters compared to two-level and non-optimized multilevel transmitters.
Figure(a) shows the simulated average transmitter efficiency of four-level burst-mode transmitters for a discrete multitone (DMT) signal with 12 dB peak-to-average power ratio (PAPR). Contour levels of 25%-60% with an interval of 5%, and 63.5% are shown in the figure. The average efficiency of 63.5% is obtained with the optimum threshold values that are obtained by the presented optimization procedure. For the given signal, an improvement of 7.6% can be obtained compared to the non-optimized case, and 42% compared to the two-level case. Figure(b) shows the spectral comparison of the optimized and the non-optimized four-level transmitters with the DMT signal of 12 dB PAPR. The dynamic range (DR) of both signal is in the same range of 30 dB. It can be seen that the optimized transmitter produces fewer out-of-band spectral components, which improve the coding efficiency and therefore the overall transmitter efficiency.
More detailed information can be found in our paper “Efficiency Optimization for Burst-Mode Multilevel Radio Frequency Transmitters” in IEEE Transactions on Circuits and Systems I.