AM-FM transmitter power amplifier

• US 5,423,074 A
• Filed: 04/11/1994
• Issued: 06/06/1995
• Est. Priority Date: 11/14/1990
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Charouel, Lisa
• Application Number:
  US08/225,709
• Time in Patent Office: 421 Days
• Field of Search: 330/129, 330/149, 330/279, 330/281, 330/298, 330/284, 330/207 P, 330/141, 330/144, 330/145, 332/149, 332/159, 455/126, 455/127, 455/113, 455/115, 455/102, 455/116, 455/107, 455/117, 455/341, 455/129, 455/74, 455/89, 455/54.1, 379/58, 379/59, 379/390, 379/403, 375/5, 375/7, 375/98, 375/60, 375/74, 375/40, 370/11
• US Class Current: 455/74
• CPC Class Codes: H03F 1/56 Modifications of input or output impedances, not otherwise provided for
• CPC Class Codes: H03H 7/38 Impedance-matching networks
• 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

Abstract

A power amplifier used in a portable, radio frequency transmitter is switched between different modes of operation when transmitting differently modulated carriers. The first mode of operation corresponds to amplitude modulation (AM), while a second mode corresponds to angle modulation techniques such as frequency modulation (FM). A switching network alters the impedance of the power amplifier to match network for matching the impedance of the transmitter antenna in order to achieve maximum efficiency in each mode of operation. Various switching methods and impedance matching circuits are disclosed.

Claims

1. A transmitter for selectively modulating a carrier signal using a variety of modulation techniques, comprising:

a power amplifier having an input for a signal to be amplified and an output for supplying an amplified signal;

a load impedance connected to said amplifier output for receiving the amplified signal; and

means for varying said load impedance based on a parameter that depends on the selected modulation technique,

wherein the power amplifier maintains a linear mode of operation when the selected modulation technique is alternatively amplitude modulation, complex modulation, and constant amplitude modulation.

2. The transmitter as defined in claim 1, wherein said modulation techniques include:

frequency modulation, the amplitude modulation, phase modulation, and the complex modulation.

3. The transmitter as defined in claim 1, wherein said parameter further depends on a power transmission level of said power amplifier.

4. The transmitter as defined in claim 1, wherein said means for varying said impedance includes a variable reactance.

5. The transmitter as defined in claim 1, wherein said load impedance includes a plurality of matching circuits and said impedance varying means switchably connects one of said matching circuits to said amplifier.

6. The transmitter as defined in claim 1, wherein said load impedance includes a plurality of harmonic filter components and said impedance varying means to switchably connects at least one of said harmonic filter components to said amplifier.