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”), comprising:
an amplifier circuit comprising a first amplifier and a second amplifier; and
a combiner network coupled to the amplifier circuit and configured to inject a second harmonic from the first amplifier into the second amplifier, the combiner network comprising an impedance transformer with a first and a second varactor in parallel,
wherein the combiner network further comprises a λ/4 transmission line or a λ/8 transmission line in parallel with a 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 first amplifier and the second signal input into the second amplifier.
3. The DPA of claim 1 , wherein the combiner network comprises both the λ/4 transmission line and the λ/8 transmission line.
4. The DPA of claim 1 , wherein the λ/4 transmission line is coupled to an output of the first amplifier to an output of the second amplifier.
5. A Doherty Power Amplifier (“DPA”), comprising:
an amplifier circuit comprising a first amplifier and a second amplifier; and
a combiner network coupled to the amplifier circuit and configured to inject a second harmonic from the first amplifier into the second amplifier, the combiner network comprising an impedance transformer with a first and a second varactor in parallel, wherein a resonant circuit comprises an open circuit at a fundamental frequency or a short circuit at the second harmonic.
6. The DPA of claim 5 , wherein the second harmonic from the first amplifier is injected at an output of the second amplifier at back-off.
7. A combiner network, comprising:
a first λ/4 transmission line coupled to a first amplifier and a second amplifier;
a second λ/4 transmission line coupled between the second amplifier and a splitter, the splitter being coupled to the first amplifier and the second amplifier;
at least one λ/8 transmission line coupled to the first λ/4 transmission line; and
a resonant circuit in parallel with the at least one λ/8 transmission line,
wherein the resonant circuit comprises a series LC resonant circuit coupled to a parallel LC resonant circuit.
8. The combiner network of claim 7 , wherein the splitter splits an RF input signal into a first and a second signal, the first signal input into the first amplifier and the second signal input into the second amplifier.
9. A combiner network, comprising:
a first λ/4 transmission line coupled to a first amplifier and a second amplifier;
a second λ/4 transmission line coupled between the second amplifier and a splitter, the splitter being coupled to the first amplifier and the second amplifier;
at least one λ/8 transmission line coupled to the first λ/4 transmission line; and
a resonant circuit in parallel with the at least one λ/8 transmission line, wherein the resonant circuit comprises an open circuit at a fundamental frequency and a short circuit at the second harmonic.
10. The combiner network of claim 7 , wherein one of the at least one λ/8 transmission line is coupled to a load.
11. The combiner network of claim 7 , wherein the first λ/4 transmission line provides a 90° phase shift.
12. A combiner network, comprising:
a first λ/4 transmission line coupled to a first amplifier and a second amplifier;
a second λ/4 transmission line coupled between the second amplifier and a splitter, the splitter being coupled to the first amplifier and the second amplifier;
at least one λ/8 transmission line coupled to the first λ/4 transmission line; and
a resonant circuit in parallel with the at least one λ/8 transmission line, wherein the first λ/4 transmission line or the at least one λ/8 transmission line comprises an impedance transformer with a first and a second varactor in parallel.
13. A method, comprising:
splitting an RF signal into a first signal and a second signal;
injecting the first signal to a first amplifier of an amplifier circuit;
injecting the second signal to a second amplifier of the amplifier circuit; and
injecting a second harmonic from the first amplifier into the second amplifier via a combiner network coupled to the amplifier circuit,
wherein the combiner network comprises a resonant circuit and at least one λ/8 transmission line in parallel with the resonant circuit.
14. The method of claim 13 , wherein the second harmonic is injected into the second amplifier during an isolation from a load.
15. The method of claim 13 , wherein the first signal and the second signal are 90° out of phase.
16. The method of claim 13 , wherein the at least one λ/8 transmission line comprises an impedance transformer with a first and a second varactor in parallel.
17. The method of claim 13 , wherein the combiner network further comprises a λ/4 transmission line coupled to the amplifier circuit and in parallel with the resonant circuit.
18. The method of claim 13 , wherein the resonant circuit comprises a series LC resonant circuit coupled to a parallel LC resonant circuit.