Nikolai Maslennikov

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.

Bias circuit topologies for minimization of RF amplifier memory effects

Memory effects in amplifiers can be described as the dependence of the output signal not only to the instantaneous input, but also to previous inputs. In a system where these effects exist, the linearity of the amplifier is degraded by the DC supply impedance, which is affected by changes in the instantaneous bandwidth of the input signal. The resulting nonlinearity is difficult to remove completely, even by the most sophisticated predistortion techniques. This paper describes a circuit technique that is readily applicable to RF amplifiers designed for wideband applications used with or without a lineariser. The memory effect reduction is achieved by placing transmission zeros in the bias network transfer function. Transmission zeros at the output of device are formed by utilizing the series resonance properties of decoupling capacitors. The frequency response is synthesized to lower and even out the impedance of the bias network over the resulting distortion bandwidth.