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Abstract

Linear power amplifiers tend to be inefficient. This is a particular problem for RF amplifiers in a cellular base station. In order to improve the efficiency of such amplifiers, attempts have been made to modulate the power supply to the amplifier proportional to the envelope of the signal to be amplified. An UMTS signal requires power supply modulation at frequencies of the order of 10 to 20 megahertz. When quantization noise is taken into account, oversampling becomes desirable. However, switching power supplies at frequencies of the order of 40 or 80 or even 160 megahertz becomes difficult. By modifying the coding of phases of the power supply to be switched so that the number of phases enabled is proportional to the desired power supply output voltage rather than the length of a pulse in a time domain on any particular phase being proportional to the output voltage, dramatic improvements are achieved in switching losses, balance between phases and accurate tracking of the input signal. Rotation of switching across the phases achieves good balance and by jittering or randomizing the rotation, switching noise may be moved out of band.

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First Claim