Dual-band doherty amplifier and method therefor
A dual-band Doherty amplifier and method therefor are provided. The dual-band Doherty amplifier includes a first amplifier gain element, a first transmission line coupled to a first output of the first amplifier gain element, a second amplifier gain element, a second transmission line coupled to a second output of the second amplifier gain element, and a controller configured, when a signal to be amplified is in a first band, to provide a first bias signal to a first bias input of the first amplifier gain element and a second bias signal to a second bias input of the second amplifier gain element and, when the signal is in a second band, to provide the second bias signal to the first bias input of the first amplifier gain element and the first bias signal to the second bias input of the second amplifier gain element.
1. A Doherty amplifier comprising:
a first Doherty amplifier gain element;
a first transmission line coupled to a first output of the first Doherty amplifier gain element, wherein the first transmission line comprises, for a first frequency band, a first series of a first number of quarter-wave transmission line elements;
a second Doherty amplifier gain element;
a second transmission line coupled to a second output of the second amplifier gain element, wherein the second transmission line comprises, for the first frequency band, a second series of a second number of quarter-wave transmission line elements, wherein the first number is not equal to the second number, wherein the first series provides, for a second frequency band, a third number of quarter-wave transmission line elements and the second series provides, for the second frequency band, a fourth number of quarter-wave transmission line elements, a first difference between the first number and the third number and a second difference between the second number and the fourth number based on a difference of wavelengths between the first band and the second band; and
a gate bias circuit for providing a first bias signal to the first Doherty amplifier gain element and a second bias signal to the second Doherty amplifier gain element when a signal being amplified by the Doherty amplifier is in the first frequency band and for providing the first bias signal to the second Doherty amplifier gain element and the second bias signal to the first Doherty amplifier gain element when the signal is in the second frequency band.
2. The Doherty amplifier of claim 1 further comprising:
a first transmission line coupled at a first end of the first transmission line to an output of the first Doherty amplifier gain element; and
a second transmission line coupled at a first end of the second transmission line to an output of the second Doherty amplifier gain element and a second end of the first transmission line is coupled to a second end of the second transmission line, wherein
the first transmission line has a first electrical length that is substantially a first odd multiple of a first quarter wavelength of the signal when the signal is in the first frequency band, and
the second transmission line has a second electrical length that is substantially a second odd multiple of a second quarter wavelength of the signal when the signal is in the second frequency band.
3. The Doherty amplifier of claim 2 wherein the second transmission line has an electrical length that is substantially a first even multiple of the first quarter wavelength of the signal when the signal is in the first frequency band and the first transmission line has an electrical length that is substantially a second even multiple of the second quarter wavelength of the signal when the signal is in the second frequency band.
4. The Doherty amplifier of claim 2 further comprising:
an adjustable amplitude and phase splitter coupled to a first input of the first Doherty amplifier gain element and to a second input of the second Doherty amplifier gain element, wherein the adjustable amplitude and phase splitter is configured to adjust a phase relationship between a first input signal at the first input and a second input signal at the second input to compensate for an approximation selected from a group consisting of a first approximation of the first electrical length to a first length and a second approximation of the second electrical length to a second length, the first length being the first odd multiple of the first quarter wavelength of the signal when the signal is in the first frequency band and the second length being the second odd multiple of the second quarter wavelength of the signal when the signal is in the second frequency band.
5. The Doherty amplifier of claim 1 wherein the first bias signal corresponds to a Class AB amplifier mode and the second bias signal corresponds to a Class C amplifier mode.
6. The Doherty amplifier of claim 1 , wherein
the first bias signal is adjusted to operate the first Doherty amplifier gain element in the first frequency band and to operate the second Doherty amplifier gain element in the second frequency band, and
the second bias signal is adjusted to operate the second Doherty amplifier gain element in the first frequency band and to operate the first Doherty amplifier gain element in the second frequency band.
7. The Doherty amplifier of claim 1 wherein the first bias signal determines operation as a Doherty carrier amplifier and the second bias signal determines operation as a Doherty peaking amplifier.
8. A method of operation in a Doherty amplifier system comprising:
determining if a signal is in a first band or in a second band;
when the signal is in the first band, providing a first bias signal to a first bias input of a first amplifier gain element of a Doherty amplifier and a second bias signal to a second bias input of a second amplifier gain element of the Doherty amplifier, wherein
a first output of the first amplifier gain element is coupled to a first series of a first number of quarter-wave transmission line elements for the first band and a second output of the second amplifier gain element is coupled to a second series of a second number of quarter-wave transmission line elements for the first band, and
the first number is not equal to the second number;
when the signal is in the second band, providing the second bias signal to the first bias input of the first amplifier gain element of the Doherty amplifier and the first bias signal to the second bias input of the second amplifier gain element of the Doherty amplifier;
providing, by the first series, a third number of quarter-transmission line elements for the second band based on difference of wavelengths between the first band and the second band; and
providing, by the second series, a fourth number of quarter-wave transmission line elements for the second band based on difference of the wavelengths between the first band and the second band.
9. The method of claim 8 further comprising:
providing a carrier amplifier signal based on the first bias signal; and
providing a peaking amplifier signal based on the second bias signal, wherein the first number of quarter-wave transmission line elements is a first odd number, the second number of quarter-wave transmission line elements is a first even number, the third number of quarter-wave transmission line elements is a second even number, and the fourth number of quarter-wave transmission line elements is a second odd number.
10. The method of claim 8 further comprising:
establishing the first series to include an entire first path from the first output of the first amplifier gain element to an output merging point and the second series to include an entire second path from the second output of the second amplifier gain element to the output merging point.
11. The method of claim 8 further comprising:
configuring a Class AB amplifier mode based on the first bias signal; and
configuring a Class C amplifier mode based on the second bias signal.
12. The method of claim 8 further comprising:
adjusting a phase difference of a first gain element input signal applied to a first input of the first amplifier gain element and a second gain element input signal applied to a second input of the second amplifier gain element to provide compensation for a first electrical length of the first series of the first number of quarter-wave transmission line elements for the first band and for a second electrical length of the second series of the second number of quarter-wave transmission line elements for the first band.
13. The method of claim 8 further comprising:
operating the first amplifier gain element as a carrier amplifier and the second amplifier gain element as a peaking amplifier for the first band; and
operating the second amplifier gain element as a carrier amplifier and the first amplifier gain element as a peaking amplifier for the second band.
14. A Doherty amplifier system comprising:
a first amplifier gain element;
a first transmission line coupled to a first output of the first amplifier gain element;
a second amplifier gain element;
a second transmission line coupled to a second output of the second amplifier gain element;
a controller coupled to a first bias input of the first amplifier gain element and to a second bias input of the second amplifier gain element, the controller configured, when a signal to be amplified by the first amplifier gain element and the second amplifier gain element is in a first band, to provide a first bias signal to the first bias input of the first amplifier gain element and a second bias signal to the second bias input of the second amplifier gain element and, when the signal is in a second band, to provide the second bias signal to the first bias input of the first amplifier gain element and the first bias signal to the second bias input of the second amplifier gain element, wherein the first transmission line comprises, for the first band, a first series of a first number of quarter-wave transmission line elements and the second transmission line comprises for the first band a second series of a second number of quarter-wave transmission line elements, wherein the first number is not equal to the second number, wherein the first series provides, for the second band, a third number of quarter-wave transmission line elements and the second series provides, for the second band, a fourth number of quarter-wave transmission line elements, a first difference between the first number and the third number and a second difference between the second number and the fourth number based on a difference of wavelengths between the first band and the second band.
15. The Doherty amplifier system of claim 14 wherein the first bias signal corresponds to a carrier amplifier signal and the second bias signal corresponds to a peaking amplifier signal, wherein first number of quarter-wave transmission line elements is a first odd number, the second number of quarter-wave transmission line elements is a first even number, the third number of quarter-wave transmission line elements is a second even number, and the fourth number of quarter-wave transmission line elements is a second odd number.
16. The Doherty amplifier system of claim 14 wherein the first bias signal corresponds to a Class AB amplifier mode and the second bias signal corresponds to a Class C amplifier mode.
17. The Doherty amplifier system of claim 14 wherein the first amplifier gain element is configured to operate as a carrier amplifier and the second amplifier gain element is configured to operate as a peaking amplifier for the first band, and the second amplifier gain element is configured to operate as a carrier amplifier and the first amplifier gain element is configured to operate as a peaking amplifier for the second band.