Doherty amplifier and power amplifier

Patent metadata

Field	Value
Publication number	US-10199994-B2
Application number	US-201515543582-A
Country	US
Kind code	B2
Filing date	Jan 16, 2015
Priority date	Jan 16, 2015
Publication date	Feb 5, 2019
Grant date	Feb 5, 2019

Abstract

A Doherty amplifier used in a Z ohm based system is provided with a carrier amplifier, a peak amplifier, and an impedance transforming line for transforming the load of the carrier amplifier when an input signal is small. The impedance transforming line has a characteristic impedance lower than Z ohms and equal to the optimum load impedance of the carrier amplifier. The load of the Doherty amplifier is lower than Z ohms. A power amplifier that obtains large output power by combining output powers from a plurality of Doherty amplifiers by a power coupling circuit is constructed.

First claim

The invention claimed is:

1. A power amplifier comprising:
a plurality of Doherty amplifiers for use in a Z-ohm system, and
a power combining circuit that includes a balun circuit and that combines output power of the plurality of Doherty amplifiers,
wherein each of the respective Doherty amplifiers comprises:
a carrier amplifier;
a peak amplifier; and
an impedance transformer line that converts a load of the carrier amplifier when an input signal is small,
wherein the impedance transformer line has a characteristic impedance smaller than Z ohms and equivalent to an optimum load impedance of the carrier amplifier,
wherein a load of the respective Doherty amplifier is smaller than Z ohms, and
wherein a load connected to a combined output terminal of the power combining circuit is Z ohms, and the balun circuit converts an impedance of the load of Z ohms so that an input impedance of an input terminal to which the respective Doherty amplifier is connected is an impedance smaller than Z ohms.

2. The power amplifier according to claim 1 ,
wherein: the Z ohms is 50 ohms, and
the optimum load impedance is five ohms or less.

3. The power amplifier according to claim 1 ,
wherein: the impedance transformer line is formed of a plurality of quarter-wavelength transformers in a cascade connection, and
the balun circuit is formed of a plurality of coupled circuits in a cascade connection.

4. The power amplifier according to claim 3 ,
wherein the plurality of coupled circuits of the balun circuit includes coupled lines with different characteristics.

5. The power amplifier according to claim 4 ,
wherein the balun circuit sets even-mode impedances in the plurality of coupled lines in a cascade connection so that levels of impedances are alternately changed in order of the cascade connection.

6. The power amplifier according to claim 5 ,
wherein a characteristic of the balun circuit is a Chebyshev response.

7. A power amplifier comprising:
a plurality of amplifiers; and
a power combining circuit that combines outputs of the plurality of amplifiers,
wherein: the plurality of amplifiers each includes
a distribution circuit that distributes an input signal inputted to an input signal terminal,
a carrier amplifier that is operated since the input signal is small,
a peak amplifier that starts operation when the input signal is high,
a phase compensation circuit that adjusts phases of an output of the carrier amplifier and an output of the peak amplifier,
a quarter-wavelength transmission line connected between the output of the carrier amplifier and the output of the peak amplifier, and
an impedance transformer connected to a node coupling the quarter-wavelength transmission line to the output of peak amplifier;

the carrier amplifier and the peak amplifier are each configured of a transistor having an optimum load impedance of five ohms or less;
the quarter-wavelength transmission line has a characteristic impedance equivalent to the optimum load impedance of the carrier amplifier smaller than five ohms, and the quarter-wavelength transmission line is directly connected to an output terminal of the carrier amplifier;
an input impedance of the power combining circuit is smaller than 50 ohms;
a load of 50 ohms is connected to an output terminal of the power combining circuit;
the quarter-wavelength transmission line and the impedance transformer are formed as a microstrip line or strip line on a first substrate, and
the power combining circuit is formed on a second substrate having a dielectric constant lower than a dielectric constant of the first substrate or having a thickness greater than a thickness of the first substrate.

8. The power amplifier according to claim 7 ,
wherein: the power amplifier is targeted to amplify a signal having an upper limit frequency almost two times a lower limit frequency or less, and
the power combining circuit includes a balun circuit that combines outputs of the plurality of amplifiers two each and that cancels a second-order harmonic produced in the plurality of amplifiers.

Assignees

• Hitachi Int Electric Inc

Inventors

• Nagasaku Toshiyuki

Classifications

• H03F1/483

  with field-effect transistors · CPC title

• H03F1/0288

  using a main and one or several auxiliary peaking amplifiers whereby the load is connected to the main amplifier using an impedance inverter, e.g. Doherty amplifiers · CPC title

• H03F1/56

  Modifications of input or output impedances, not otherwise provided for · CPC title

• H03F1/486 Primary

  with IC amplifier blocks · CPC title

• H03F3/19

  with semiconductor devices only · CPC title