Mark Gurvich

Enhancement of power amplifier efficiency through dynamic bias switching

Linear digital modulation techniques in modern communication systems generate carrier signals with relatively high peak-to-average ratio. For linear amplification of such a signal, power amplifier must be operated at excessive back off, thus sacrificing the overall amplifier efficiency. Dynamic bias switching (DBS) can be used to enhance the efficiency of PA and the means to combat the degradation of spectrum regrowth and in-band noise are discussed in this paper. DBS is achieved by partitioning the required supply rail into two or several levels. The supply voltage is switched between the steps, and is adjusted in tune with the signal envelope. This is accomplished by using a pass-transistor (gate) operated as a switch with very low channel resistance. This approach avoids the energy loss associated with continuous tracking (amplification) of the signal envelope reported in the literature.

Error signal reuse in a feedforward amplifier

In this paper, the concept of frequency selective feedback is examined in the context of feedforward (FFWD) amplifier architecture. In a typical FFWD system, a time-delayed signal that represents the distortion products is injected in anti-phase at the main amplifier output, thus improving the overall intermodulation distortion (IMD) of the system. This signal may also be reused as a feedback signal for improving the uncorrected main amplifier performance. Main amplifier linearity improvement is important in terms of efficiency, size and cost, and can be achieved at a small price in terms of added complexity. This paper presents simulation and measured results that were obtained from a realized system. The practical limitations of this technique are also outlined.