Doherty power amplifier with integrated second harmonic injection
Examples disclosed herein relate to a Doherty Power Amplifier (“DPA”) with integrated second harmonic injection. The DPA includes an amplifier circuit having a carrier amplifier and a peaking amplifier, and a combiner network coupled to the amplifier circuit, the combiner network having a plurality of transmission lines and a LC resonant circuit to inject a second harmonic from the carrier amplifier into the peaking amplifier.
1. A Doherty Power Amplifier (“DPA”) with integrated second harmonic injection, comprising:
an amplifier circuit comprising a carrier amplifier and a peaking amplifier; and
a combiner network coupled to the amplifier circuit, the combiner network having a plurality of transmission lines and a LC resonant circuit to inject a second harmonic from the carrier amplifier into the peaking amplifier, wherein the plurality of transmission lines comprises at least one λ/8 transmission line in parallel with the LC resonant circuit.
2. The DPA of claim 1 , wherein the amplifier circuit further comprises a splitter to split an RF input signal into a first and a second signal 90° out of phase, the first signal input into the carrier amplifier and the second signal input into the peaking amplifier.
3. The DPA of claim 1 , wherein the plurality of transmission lines further comprises a first λ/4 transmission line in parallel with the LC resonant circuit.
4. The DPA of claim 1 , wherein a transmission line in the plurality of transmission lines comprises an impedance transformer with a first and a second varactor in parallel.
5. The DPA of claim 1 , wherein the LC resonant circuit comprises an open circuit at a fundamental frequency.
6. The DPA of claim 1 , wherein the LC resonant circuit comprises a short circuit at a second harmonic.
7. The DPA of claim 3 , wherein the first λ/4 transmission line couples an output of the carrier amplifier to an output of the peaking amplifier.
8. The DPA of claim 3 , wherein the first λ/4 transmission line provides a 90° phase shift.
9. The DPA of claim 1 , wherein the second harmonic signal from the carrier amplifier is injected at an output of the peaking amplifier at back-off.
10. A combiner network to increase the efficiency of a Doherty Power Amplifier (“DPA”) for use in millimeter wave applications, the combiner network comprising:
a first λ/4 transmission line coupled to a carrier amplifier and a peaking amplifier;
a second λ/8 transmission line coupled to the first λ/4 transmission line;
a third λ/8 transmission line coupled to the second λ/8 transmission line; and
an LC resonant circuit in parallel with the second and third λ/8 transmission lines, wherein one of the first λ/4 transmission line, the second λ/8 transmission line, or the third λ/8 transmission line comprises an impedance transformer with a first and a second varactor in parallel.
11. The combiner network of claim 10 , wherein the carrier amplifier and the peaking amplifier are coupled to a splitter.
12. The combiner network of claim 11 , wherein the splitter is to split an RF input signal into a first and a second signal, the first signal input into the carrier amplifier and the second signal input into the peaking amplifier.
13. The combiner network of claim 11 , further comprising a fourth λ/4 transmission line coupled between the splitter and the peaking amplifier.
14. The combiner network of claim 10 , wherein the LC resonant circuit comprises a series LC resonant circuit coupled to a parallel LC resonant circuit.
15. The combiner network of claim 10 , wherein the LC resonant circuit comprises an open circuit at a fundamental frequency and a short circuit at the second harmonic.
16. The combiner network of claim 10 , wherein the third λ/8 transmission line is coupled to a load.
17. A method to increase the efficiency of a Doherty Power Amplifier (“DPA”) for use in millimeter wave applications, the method comprising:
providing an amplifier circuit with a carrier amplifier and a peaking amplifier;
coupling a combiner network to the amplifier circuit via a transmission line comprising an impedance transformer with a first and a second varactor in parallel; and
injecting a second harmonic from the carrier amplifier into the peaking amplifier at back-off to increase a back-off efficiency of the peaking amplifier.
18. The method of claim 17 , wherein coupling the combiner network to the amplifier circuit comprises coupling a first λ/4 transmission line to the carrier amplifier and the peaking amplifier.
19. The method of claim 18 , wherein coupling the combiner network to the amplifier circuit further comprises coupling the first λ/4 transmission line to an LC resonant circuit in parallel with a second and a third λ/8 transmission lines.
20. The method of claim 17 , wherein injecting a second harmonic comprises injecting the second harmonic into the peaking amplifier during isolation from a load.