RF power amplifier with frequency selective impedance matching network
An amplifier circuit includes an input port, an output port, and a reference potential port, an RF amplifier device having an input terminal electrically coupled to the input port, an output terminal electrically coupled to the output port, and a reference potential terminal electrically coupled to the reference potential port. An impedance matching network is electrically connected to the output terminal, the reference potential port, and the output port. The impedance matching network includes a reactive efficiency optimization circuit that forms a parallel resonant circuit with a characteristic output impedance of the peaking amplifier at a center frequency of the fundamental frequency range. The impedance matching network includes a reactive frequency selective circuit that negates a phase shift of the RF signal in phase at the center frequency and exhibits a linear transfer characteristic in a baseband frequency range.
1. An amplifier circuit, comprising:
an RF amplifier comprising an input terminal, an output terminal, and a reference potential terminal, the RF amplifier configured to amplify an RF signal across a fundamental frequency range; and
an impedance matching network electrically connected to the output terminal and the reference potential terminal, the impedance matching network configured to:
match a characteristic output impedance of the RF amplifier at a center frequency of the fundamental frequency range;
provide an RF signal at an intrinsic node of the RF amplifier substantially in phase with an RF signal at the output port at the center frequency; and
exhibit a linear transfer characteristic in a baseband frequency range below the fundamental frequency range.
2. The amplifier circuit of claim 1 , wherein the impedance matching network comprises:
an efficiency optimization circuit connected in parallel with the output terminal and the reference potential terminal, and configured to match the characteristic output impedance; and
a frequency selective circuit connected in series between the output terminal and an output port of the amplifier circuit, and configured to provide the RF signal at the intrinsic node substantially in phase with the RF signal at the output port and to exhibit the linear transfer characteristic in the baseband frequency range.
3. The amplifier circuit of claim 2 , wherein the frequency selective circuit comprises a capacitor and an inductor electrically connected in parallel with one another, and wherein the capacitor and the inductor are each electrically connected in series between the output terminal and the output port.
4. The amplifier circuit of claim 3 , wherein parameter values of the capacitor and the inductor are such that:
the capacitor provides a dominant transmission path for the RF signal in the fundamental frequency range; and
the inductor provides a dominant transmission path for the RF signal in the baseband frequency range.
5. The amplifier circuit of claim 3 , wherein the impedance matching network comprises a parasitic inductance connected in series between the output terminal and the output port, and wherein parameter values of the capacitor and the inductor are selected such that the parasitic inductance, the capacitor, and the inductor collectively provide substantially zero phase shift to the RF signal between the intrinsic node and the output port at the center frequency.
6. The amplifier circuit of claim 2 , wherein parameter values of the frequency selective circuit are selected to shift a non-linear transfer characteristic region of the impedance matching network into a frequency range that is between the baseband frequency range and the fundamental frequency range.
7. The amplifier circuit of claim 6 , wherein the fundamental frequency range comprises frequencies in the range of 1.8-2.7 GHz, and wherein the baseband frequency range comprises frequencies in the range of 0-900 MHz.
8. An amplifier circuit, comprising:
an RF amplifier comprising an input terminal, an output terminal, and a reference potential terminal, the RF amplifier configured to amplify an RF signal across a fundamental frequency range; and
an impedance matching network electrically connected to the output terminal and the reference potential terminal, the impedance matching network configured to:
form a parallel resonant circuit with a characteristic output impedance of the RF amplifier at a center frequency of the fundamental frequency range,
form a first transmission path with a substantially zero phase shift between an intrinsic node of the RF amplifier and the output port at the center frequency, and
form a second transmission path with a low impedance DC connection between the output terminal and the output port to pass DC signals between the output terminal and the output port.
9. The amplifier circuit of claim 8 wherein the impedance matching network comprises:
a parallel branch, connected between the output terminal and the reference potential terminal, that forms the parallel resonant circuit; and
a series branch, connected in series between the output terminal and an output port of the amplifier circuit, the series branch comprising the first transmission path and the second transmission path.
10. The amplifier circuit of claim 9 , wherein the series branch comprises capacitor connected in parallel with an inductor, wherein the first transmission path comprises the capacitor, and wherein the second transmission path comprises the inductor.
11. The amplifier circuit of claim 10 , wherein the impedance matching network comprises a parasitic inductance connected in series between the output terminal and the output port, and wherein the capacitor and the inductor are configured such that the parasitic inductance, the capacitor, and the inductor collectively provide the substantially zero phase shift to the RF signal between the intrinsic node and the output port at the center frequency.
12. The amplifier circuit of claim 8 , wherein the impedance matching network is devoid of an independent DC feeding network.
13. A Doherty Amplifier circuit, comprising:
a main amplifier configured to amplify an RF signal between a main input terminal and a main output terminal across a fundamental frequency range;
a peaking amplifier configured to amplify the RF signal between a peaking input terminal and a peaking output terminal across the fundamental frequency range;
an impedance transformer connected between the main output terminal and a combiner node; and
an impedance matching network connected between the peaking output terminal and the combiner node configured to:
form a parallel resonant circuit with a characteristic output impedance of the peaking amplifier at a center frequency of the fundamental frequency range;
provide an RF signal at an intrinsic node of the peaking amplifier substantially in phase with an RF signal at the combiner node at the center frequency; and
exhibit a substantially linear transfer characteristic in a baseband frequency range below the fundamental frequency range.
14. The Doherty Amplifier circuit of claim 13 , wherein the impedance matching network comprises:
an efficiency optimization circuit configured to form the parallel resonant circuit with the characteristic output impedance of the peaking amplifier at the center frequency of the fundamental frequency range; and
a frequency selective circuit configured to;
provide the RF signal at the intrinsic node of the peaking amplifier substantially in phase with the RF signal at the combiner node at the center frequency; and
exhibit the substantially linear transfer characteristic in the baseband frequency range.
15. The Doherty Amplifier circuit of claim 14 , wherein the frequency selective circuit comprises a capacitor and an inductor electrically connected in parallel with one another, and wherein the capacitor and the inductor are each electrically connected in series between the peaking output terminal and the combiner node.
16. The Doherty Amplifier circuit of claim 15 , wherein parameter values of the second capacitor and the inductor are selected such that:
the capacitor provides a dominant transmission path for the RF signal in the fundamental frequency range; and
the inductor provides a dominant transmission path for the RF signal in the baseband frequency range.
17. The Doherty Amplifier circuit of claim 15 , wherein the impedance matching network comprises a parasitic inductance connected in series between the peaking output terminal and the combiner node, and such that the parasitic inductance, the capacitor, and the inductor collectively provide substantially zero phase shift to the RF signal between the intrinsic node and the combiner node at the center frequency.