Wideband doherty amplifier circuit with peaking impedance absorption
View Patent ↗A wideband Doherty amplifier circuit includes a main amplifier configured to operate in a linear mode, a peaking amplifier configured to operate in a non-linear mode and a Doherty combiner directly connected to an output of each amplifier so that no output match devices are in the path between the amplifier outputs and the Doherty combiner. The Doherty combiner is configured to present the same load impedance to each amplifier when both amplifiers are conducting and present a modulated load impedance to the main amplifier when the peaking amplifier is non-conducting so that a variation in the VSWR seen by the main amplifier is less than 5% over a plurality of frequency bands and/or so that the peaking amplifier has an off-state impedance spreading of 20 degrees or less over the plurality of frequency bands.
1. A wideband Doherty amplifier circuit, comprising:
a main amplifier configured to operate in a linear mode;
a peaking amplifier configured to operate in a non-linear mode; and
a Doherty combiner directly connected to an output of each amplifier so that no output match devices are in the path between the amplifier outputs and the Doherty combiner, the Doherty combiner configured to present the same load impedance to each amplifier when both amplifiers are amplifying and present a modulated load impedance to the main amplifier when the peaking amplifier is not amplifying so that the variation in a voltage standing wave ratio (VSWR) seen by the main amplifier is less than 5% over a plurality of frequency bands,
wherein the main amplifier has an optimal output impedance Z 1 and size T 1 , the peaking amplifier has an optimal output impedance Z 2 and size T 2 , the Doherty combiner comprises a transmission line having an impedance Z 3 directly connected to the output of the main amplifier at one end and directly connected to the output of the peaking amplifier at an opposing end, and
Z
3
=
(
Z
1
×
Z
2
×
T
2
T
1
)
1
2
.
2. A wideband Doherty amplifier circuit according to claim 1 , wherein the Doherty combiner is configured to ensure the variation in the VSWR seen by the main amplifier is less than 3% over the plurality of frequency bands.
3. A wideband Doherty amplifier circuit according to claim 1 , wherein Z 1 =2×Z 2 and T 2 =2×T 1 .
4. A wideband Doherty amplifier circuit according to claim 1 , wherein the Doherty combiner further comprises a tapered impedance transformer having a wider end connected to the output of the peaking amplifier and a narrower end connected to a load.
5. A wideband Doherty amplifier circuit according to claim 1 , further comprising an additional peaking amplifier configured to operate in a non-linear mode so that the wideband Doherty amplifier circuit has a first power mode corresponding to the main amplifier amplifying and the peaking amplifiers not amplifying, a second power mode corresponding to the main amplifier amplifying and one of the peaking amplifiers amplifying, and a third power mode corresponding to the main amplifier amplifying and both peaking amplifiers amplifying, wherein the Doherty combiner is configured to ensure the variation in the VSWR seen by the main amplifier is less than 5% over the plurality of frequency bands.
6. A wideband Doherty amplifier circuit according to claim 5 , wherein the additional peaking amplifier has an optimal output impedance Z 4 and size T 4 , the Doherty combiner further comprises an additional transmission line having an impedance Z 5 directly connected to the output of the peaking amplifier at one end and directly connected to the output of the additional peaking amplifier at an opposing end, and
Z
5
=
(
Z
2
×
Z
4
×
T
2
T
1
×
T
4
T
1
[
1
+
T
2
T
1
]
2
)
1
/
2
.
7. A wideband Doherty amplifier circuit according to claim 6 , wherein Z 1 =2×Z 2 , T 2 =2×T 1 , Z 2 =Z 4 , and T 2 =T 4 .
8. A wideband Doherty amplifier circuit according to claim 6 , wherein the Doherty combiner further comprises a tapered impedance transformer having a wider end connected to the output of the additional peaking amplifier and a narrower end connected to a load.
9. A wideband Doherty amplifier circuit, comprising:
a main amplifier configured to operate in a linear mode;
a peaking amplifier configured to operate in a non-linear mode;
a Doherty combiner directly connected to an output of each amplifier so that no output match devices are in the path between the amplifier outputs and the Doherty combiner, the Doherty combiner configured to present the optimal load impedance to each amplifier when both amplifiers are conducting and present a modulated load impedance to the main amplifier when the peaking amplifier is not amplifying so that the peaking amplifier has an off-state impedance spreading of 20 degrees or less over a plurality of frequency bands; and
an additional peaking amplifier configured to operate in a non-linear mode so that the wideband Doherty amplifier circuit has a first power mode corresponding to the main amplifier amplifying and the peaking amplifiers not amplifying, a second power mode corresponding to the main amplifier amplifying and one of the peaking amplifiers amplifying, and a third power mode corresponding to the main amplifier amplifying and both peaking amplifiers also amplifying, wherein the Doherty combiner is configured to ensure the peaking amplifiers have an off-state impedance spreading of 20 degrees or less over the plurality of frequency bands.
10. A wideband Doherty amplifier circuit, comprising:
a main amplifier configured to operate in a linear mode and having an optimal output impedance Z 1 and size T 1 ;
a peaking amplifier configured to operate in a non-linear mode and having an optimal output impedance Z 2 and size T 2 ; and
a Doherty combiner comprising a transmission line having an impedance Z 3 directly connected to the output of the main amplifier at one end and directly connected to the output of the peaking amplifier at an opposing end so that no output match devices are in the path between the amplifier outputs and the Doherty combiner,
wherein
Z
3
=
(
Z
1
×
Z
2
×
T
2
T
1
)
1
2
.
11. A wideband Doherty amplifier circuit according to claim 10 , wherein Z 1 =2×Z 2 and T 2 =2×T 1 .
12. A wideband Doherty amplifier circuit according to claim 10 , wherein the Doherty combiner further comprises a tapered impedance transformer having a wider end connected to the output of the peaking amplifier and a narrower end connected to a load.
13. A wideband Doherty amplifier circuit according to claim 10 , further comprising an additional peaking amplifier configured to operate in a non-linear mode and having an optimal output impedance Z 4 and size T 4 , wherein the Doherty combiner further comprises an additional transmission line having an impedance Z 5 directly connected to the output of the peaking amplifier at one end and directly connected to the output of the additional peaking amplifier at an opposing end, and
Z
5
=
(
Z
2
×
Z
4
×
T
2
T
1
×
T
4
T
1
[
1
+
T
2
T
1
]
2
)
1
/
2
.
14. A wideband Doherty amplifier circuit according to claim 13 , wherein Z 1 =2×Z 2 , T 2 =2×T 1 , Z 2 =Z 4 , and T 2 =T 4 .
15. A wideband Doherty amplifier circuit according to claim 13 , wherein the Doherty combiner further comprises a tapered impedance transformer having a wider end connected to the output of the additional peaking amplifier and a narrower end connected to a load.
16. A wideband Doherty amplifier circuit according to claim 10 , wherein the Doherty combiner is configured to present the same load impedance to each amplifier when both amplifiers are conducting and present a modulated load impedance to the main amplifier when the peaking amplifier is non-conducting so that a variation in a voltage standing wave ratio (VSWR) seen by the main amplifier is less than 5% over the plurality of frequency bands.
17. A wideband Doherty amplifier circuit according to claim 10 , wherein the Doherty combiner is configured to present the same load impedance to each amplifier when both amplifiers are conducting and present a modulated load impedance to the main amplifier when the peaking amplifier is non-conducting so that the peaking amplifier has an off-state impedance spreading of 20 degrees or less over the plurality of frequency bands.
18. A wideband Doherty amplifier circuit according to claim 10 , wherein the transmission line of the Doherty combiner is directly wire bonded to the output of the main amplifier at one end and directly wire bonded to the output of the peaking amplifier at the other end.