Efficiency and linearity of the microwave power amplifier are critical elements for mobile communication systems. This paper discusses improvements in system efficiency that are obtainable when a dc-dc converter is used to convert available battery voltage to an optimal supply voltage for the output RF amplifier. A boost dc-dc converter with an operating frequency of 10 MHz is demonstrated using GaAs heterojunction bipolar transistors. Advantages of 10-MHz switching frequency and associated loss mechanisms are described. For modulation formats with time-varying envelope, such as CDMA, the probability of power usage is described. Gains in power efficiency and battery lifetime are calculated. An envelope detector circuit with a fast feedback loop regulator is discussed. Effects of varying supply voltage with respect to distortion are examined along with methods to increase system linearity.

A novel amplifier configuration is described, in which a bandpass delta-sigma modulator is used to produce a two-level (digital) signal representing an analog radio frequency (RF) input. Subsequently, a switching-mode amplifier and bandpass filter are used to amplify the signal and remove unwanted spectral components. This configuration has the potential of achieving high efficiency (typical of switching mode amplifiers) together with high linearity. A simulated implementation with GaAs heterojunction bipolar transistors (HBT) is shown.

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This paper presents a technique for raising power efficiency in portable wireless transmitters by integrating a variable voltage output dc-dc converter together with a MESFET F W power amplifier. Significant increases in power efficiency are obtainable over a large range of output power levels. The system includes an envelope detector, a closed feedback loop, and a pulse width modulator operating at 10 MHz. A 300mW transmitter is shown for which battery life can be extended by over 1.4 times. PowerHigh wastf!d ef'ficierq

ABSTRQCT -It is shown a simple extension of the conventional behavioral characterization of amplifier nonlinearity can be used to quantify power amplifier performance including many memory effects. External variables that influence the amplifier behavior (such as power supply voltage, input bias or temperature) are identified. Measurements of gain and phase (AM-AM and AM-PMconversion) are subsequently made over a range of these external variables. The variation of the external variables is explicitly taken into account with linear equivalent circuits at baseband. The method is shown to be useful for the estimation of bias circuit effects and self-heating effects.,

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