Enhanced and versatile N-way doherty power amplifier
The output of a carrier amplifier circuit in a Doherty amplifier is coupled to the summing node so that the impedance observed by the carrier amplifier's output is approximately equal to the load impedance at the combining node when the load impedance is not modulated. In an example non-inverting configuration, a power amplifier circuit is configured to provide an amplified signal to a load at a summing node, where the load has a first impedance when not load-modulated. The power amplifier circuit includes a splitter network arranged to receive the input signal and to split the input signal to provide a carrier input signal and a peaking input signal, a carrier amplifier path configured to amplify the carrier input signal in a full-power mode and in a first backoff mode, and a peaking amplifier path configured to amplify the peaking input signal in at least the full-power mode.
1. A power amplifier circuit for amplifying an input signal and providing an amplified signal to a load at a summing node, wherein the load at the summing node has a first impedance when not load-modulated, the power amplifier circuit comprising:
a splitter network arranged to receive the input signal and to split the input signal to provide a carrier input signal and a peaking input signal;
a carrier amplifier path configured to amplify the carrier input signal in a full-power mode and in a first backoff mode and comprising a carrier amplifier circuit and a first impedance transformer in series with an output of the carrier amplifier circuit and connected directly to the summing node, the first impedance transformer having a phase length approximately equal to or greater than ninety degrees, at a nominal operating frequency for the power amplifier circuit, and having a designed characteristic impedance value approximately equal to the first impedance;
a peaking amplifier path configured to amplify the peaking input signal in at least the full-power mode and comprising a selectively activatable peaking amplifier circuit configured to be activated in the full-power mode and to be de-activated in at least a first backoff mode, wherein an output of the selectively activatable peaking amplifier circuit is coupled to the summing node; and
a delay line coupling the output of the carrier amplifier circuit to the first impedance transformer, the delay line having a characteristic impedance approximately equal to the first impedance, wherein the delay line has a phase length substantially shorter than ninety degrees, at a nominal operating frequency for the power amplifier circuit.
2. The power amplifier circuit of claim 1 , wherein the delay line has a length such that a second impedance presented to the output of the carrier amplifier, when the power amplifier circuit is operating in the full-power mode, is shifted, relative to the first impedance, towards an optimal matching impedance for the output of the carrier amplifier.
3. The power amplifier circuit of claim 1 , wherein the splitter network is further arranged to provide a second peaking amplifier input signal, and wherein the power amplifier circuit further comprises:
a second peaking amplifier path configured to selectively amplify the second peaking amplifier input signal in the peaking mode and in the first backoff mode and to be deactivated in at least a second backoff mode, the second peaking amplifier path comprising a second selectively activatable peaking amplifier circuit having an output coupled to the summing node.
4. A power amplifier circuit for amplifying an input signal and providing an amplified signal to a load at a summing node, wherein the load at the summing node has a first impedance when not load-modulated the power amplifier circuit comprising:
a splitter network arranged to receive the input signal and to split the input signal to provide a carrier input signal and a peaking input signal;
a carrier amplifier path configured to amplify the carrier input signal in a full-power mode and in each of one or more backoff modes and comprising a carrier amplifier circuit having an output coupled to the summing node via a delay line having a characteristic impedance approximately equal to the first impedance, so that an impedance presented to the output is substantially equal to the first impedance when the load at the summing node is not load-modulated; and
a first peaking amplifier path configured to amplify the peaking input signal in at least the full-power mode and comprising a first selectively activatable peaking amplifier circuit configured to be activated in the full-power mode and to be de-activated in at least a first backoff mode, wherein an output of the first selectively activatable peaking amplifier circuit is coupled to the summing node via a first impedance transformer connected directly to the summing node and having a phase length approximately equal to or greater than ninety degrees, at the nominal operating frequency for the power amplifier circuit, and having a designed characteristic impedance value substantially greater than the first impedance.
5. The power amplifier circuit of claim 4 , wherein the first impedance transformer has a designed characteristic impedance value selected so as to match a load-modulated impedance at the summing node.
6. The power amplifier circuit of claim 4 , wherein the first impedance transformer has a designed characteristic impedance value substantially greater than a fully-load-modulated impedance at the summing node.
7. The power amplifier circuit of claim 4 , wherein the delay line has a phase length substantially shorter than ninety degrees, at a nominal operating frequency for the power amplifier circuit.
8. The power amplifier circuit of claim 4 , wherein the splitter network is further arranged to provide a second peaking amplifier input signal, and wherein the power amplifier circuit further comprises:
a second peaking amplifier path configured to selectively amplify the second peaking amplifier input signal in the peaking mode and in the first backoff mode and to be deactivated in at least a second backoff mode, the second peaking amplifier path comprising a second selectively activatable peaking amplifier circuit having an output coupled to the summing node.