Radio frequency power amplifier and method using an amplitude control system

Abstract

A radio frequency power amplifier and corresponding method is arranged and configured to drive a resonant load. The radio frequency power amplifier includes a radio frequency switching stage with an output that is coupled to a resonant circuit. The switching stage is configured to provide an output signal with amplitude modulation corresponding to amplitude modulation of an input signal when powered from a fixed voltage power supply. The amplifier further includes a feedback control system coupled to the input signal and the output signal, where the feedback control system includes a sequencer configured to provide a sequencer output that is used to drive the radio frequency switching stage. The amplifier also includes an amplitude control system coupled to the output of the radio frequency switching stage and configured to limit an amplitude of the output signal and in some embodiments a power recovery system.

Description

RELATED APPLICATIONS [0001] This application is a continuation in part of pending application titled RADIO FREQUENCY POWER AMPLIFIER AND CORRESPONDING METHOD, Ser. No. 11 / 089,834 by Snelgrove et al., filed on Mar. 25, 2005, which is hereby incorporated herein in its entirety by reference. This application is related to co-pending application titled RADIO FREQUENCY POWER AMPLIFIER AND METHOD USING A PLURALITY OF FEEDBACK SYSTEMS, Docket number 34-003P01 filed Apr. 28, 2006, which is hereby incorporated herein in its entirety by reference. This application also claims priority from Provisional Application, Ser. No. 60 / 675,614, filed on Apr. 28, 2005 and Provisional Application, Ser. No. 60 / 675,704, filed on Apr. 28, 2005, which are also hereby incorporated herein in their entirety by reference.FIELD OF THE INVENTION [0002] This invention relates in general to communication equipment, and more specifically to radio frequency power amplifiers. BACKGROUND OF THE INVENTION [0003] Radio-fr...

AI Technical Summary

Problems solved by technology

Small distortions in the form of the output signal relative to the input can cause the radio frequency power amplifier output signal to interfere with other radio services, in violation of regulatory requirements, or make it difficult or impossible to receive / demodulate the signal accurately.

These distortions may be caused, for example, by the fact that the characteristics of the components of which a radio frequency power amplifier is composed (e.g. transistors) are non-ideal, e.g., vary with the electrical currents that they carry, which necessarily include the signal being reproduced.

The power (90 Watts in the example) “wasted” in this way causes many problems.

When equipment is battery-operated (e.g. in cell phones or in fixed installations (base transmitters) that are running on backup batteries during a power failure), battery size and hence weight and cost increases directly with power requirements.

However, class E amplifiers pose problems.

For example, since their output power is effectively set by a power supply voltage, they are difficult to amplitude-modulate and attempts to do so have resulted in both poor efficiency and poor linearity.

The inability to modulate amplitude severely limits the applicability of class E amplifiers in most modern systems employing complex forms of modulation with varying amplitude or amplitude inverting signals.

In practice, Class D amplifiers are continually discharging capacitance (e.g., when turned on) and this can amount to significant power dissipation at radio frequencies.

This causes problems for class E radio frequency power amplifiers since their inputs need to be synchronized with a high frequency signal.

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