Radio frequency power amplifier having variable output power

• US 5,276,912 A
• Filed: 04/01/1993
• Issued: 01/04/1994
• Est. Priority Date: 02/06/1990
• Status: Expired due to Fees

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Siwiak, Kazimierz, Minasi, David H.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): FAILE, ANDREW I
• Application Number:
  US08/041,525
• Time in Patent Office: 278 Days
• Field of Search: 455/69, 455/107, 455/115-116, 455/126, 455/127, 455/129, 455/341, 455/343, 455/73, 330/51, 330/278, 330/279, 330/282, 330/284, 330/285, 330/302, 330/86, 330/124 R, 333/17.3, 333/32
• US Class Current: 455/73
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H04B 1/0458 Arrangements for matching and coupling between power amplifier and antenna or between amplifying stages matching circuits in general H03H
• CPC Class Codes: H04B 2001/0416 having gain or transmission power control

Abstract

A radio-frequency amplifier (50) has an impedance transformation network (66) with a control input (70) for controlling the transformation characteristic of the transformation network (66). The radio-frequency amplifier (50) amplifies an input signal to produce an amplified radio-frequency output signal to a load (68). The control circuit selects a power level for the output signal, in response to a control signal, by transforming the impedance of the load to a transformed impedance at the output of the radio-frequency amplifier, so that the efficiency of the radio-frequency amplifier is not substantially degraded as the power level for the output signal is changed.

Claims

1. A radio-frequency amplifier circuit for providing an amplified radio-frequency signal to a load having a load impedance, the radio-frequency amplifier circuit comprising:

amplifier means for amplifying an input signal to produce the amplified radio-frequency signal to the load, the amplifier means operating in a high efficiency switching mode and having an input for receiving the input signal, and having an output to provide the amplified radio-frequency signal, the amplified radio-frequency signal having variable output power;

transformation means for transforming the load impedance of the load to a transformed impedance at the output of the amplifier means responsive to a control signal, the transformation means having a control input for receiving the control signal to set a selected power level for the amplified radio-frequency signal, the transformation means having a predetermined transforming characteristic for transforming the load impedance to allow the amplifier means to remain saturated at the selected power level, the saturation of the amplifier means provides for operation at maximum efficiency and not just maximum power transfer available with matched impedance and;

control means for providing the control signal.

2. A radio transceiver, comprising:

a radio-frequency amplifier having an input and an output, for amplifying an input signal to produce an output signal to a load, the load having a load impedance;

transformation means for transforming the load impedance of the load to a transformed impedance at the output of the amplifier means responsive to a control signal, the transformation means having a control input for receiving the control signal to set a power level from a plurality of power levels for the amplified radio-frequency signal, so that the efficiency of the radio-frequency amplifier is not substantially degraded as the power level of the output signal is reduced and the transformation means having a predetermined transforming characteristic for transforming the load impedance to allow the amplifier means to remain saturated and operate with maximum efficiency at all the plurality of power levels; and

control means for providing the control signal.

3. The radio transceiver of claim 2 wherein the radio-frequency amplifier comprises:

a plurality of series-connected amplifier stages;

means for switching off and bypassing at least one of the amplifier stages in response to the control signal.