Doherty combiner

1. A Doherty combiner comprising:

a phase shift section connected between one end of a carrier amplifier and a common node so as to change a phase of an RF signal output from the carrier amplifier;

a matching section connected between the common node and an output terminal of a Doherty power amplifier so as to impedance-match an output of the Doherty power amplifier; and

a bandwidth improvement section connected between one end of a peaking amplifier and the common node so as to change at least one of a phase bandwidth and a magnitude bandwidth of the Doherty power amplifier,

wherein the common node indicates one point where one end of the phase shift section, one end of the matching section, and one end of the bandwidth improvement section meet one another.

2. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a 180° phase shift line.

3. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a 180° phase shift line connected to one end of the peaking amplifier and a parallel resonant circuit connected to the 180° phase shift line.

4. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a 180° phase shift line connected to one end of the peaking amplifier and a short stub connected to the 180° phase shift line.

5. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a serial resonant circuit in which an inductor L and a capacitor C are connected in series.

6. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a serial resonant circuit in which a first inductor and a first capacitor are connected in series and a parallel resonant circuit in which a second inductor and a second capacitor are connected in parallel.

7. The Doherty combiner of claim 5 , wherein the phase shift section includes a first transmission line for combining outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second transmission line for impedance-matching the output of the Doherty power amplifier.

8. The Doherty combiner of claim 5 , wherein the phase shift section includes first lumped elements having an equivalent relationship to a transmission line for combining the outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second lumped element having an equivalent relationship to a transmission line for impedance-matching the output of the Doherty power amplifier.

9. The Doherty combiner of claim 8 , wherein the first lumped element is configured by any one of a Low-Pass π Type LC circuit, a High-Pass π Type LC circuit, a Low-Pass T Type LC circuit, and a High-Pass T Type LC circuit, and

the second lumped element is configured by any one of a Low-Pass π Type LC circuit, a High-Pass π Type LC circuit, a Low-Pass T Type LC circuit, and a High-Pass T Type LC circuit.

10. The Doherty combiner of claim 9 , wherein the second lumped element has a different L/C value from the first lumped element.

11. The Doherty combiner of claim 5 , wherein the phase shift section includes a first lumped element and a first resonant circuit having the equivalent relationship to the transmission line for combining the outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second lumped element and a second resonant circuit having the equivalent relationship to the transmission line for impedance-matching the output of the Doherty power amplifier.

12. The Doherty combiner of claim 11 , wherein when the first or second lumped element is a π type structure, the first or second resonant circuit is the parallel resonant circuit, and

when the first or second lumped element is a T type structure, the first or second resonant circuit is the serial resonant circuit.

13. The Doherty combiner of claim 11 , wherein the second resonant circuit has the same L/C value as the first resonant circuit.

14. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a serial resonant circuit in which the inductor and the capacitor are connected in series and a short stub connected to the serial resonant circuit.

15. The Doherty combiner of claim 1 , wherein the bandwidth improvement section includes a distributed element circuit having the equivalent relationship to a lumped element circuit corresponding to the serial resonant circuit.

16. The Doherty combiner of claim 15 , wherein the distributed element circuit includes two transmission lines and capacitors equally substituted by Kuroda's Identities.

17. The Doherty combiner of claim 6 , wherein the phase shift section includes a first transmission line for combining outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second transmission line for impedance-matching the output of the Doherty power amplifier.

18. The Doherty combiner of claim 6 , wherein the phase shift section includes first lumped elements having an equivalent relationship to a transmission line for combining the outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second lumped element having an equivalent relationship to a transmission line for impedance-matching the output of the Doherty power amplifier.

19. The Doherty combiner of claim 6 , wherein the phase shift section includes a first lumped element and a first resonant circuit having the equivalent relationship to the transmission line for combining the outputs of the carrier amplifier and the peaking amplifier, and

the matching section includes a second lumped element and a second resonant circuit having the equivalent relationship to the transmission line for impedance-matching the output of the Doherty power amplifier.