High linearity satellite payload using solid state power amplifiers
A solid state power amplifier uses a Doherty power amplifier that can be implemented as a monolithic microwave integrated circuit. By adjusting the DC bias of the amplifying stages in each branch of the Doherty amplifier, the output power, linearity, and DC power can be adjusted to provide a specified output, where the specification for the output can include the maintaining of desired DC power and linearity. The Doherty power amplifier can be used in a satellite payload or other application utilizing solid state power amplifiers, while providing the proper amount of RF output power and DC power. A single amplifier can have its bias levels adjusted for different output levels, helping to minimize the number of designs that are required for a given satellite payload, reducing the variety of parts in a satellite payload.
1. A satellite, comprising:
a plurality of receive antennae;
a plurality of transmit antennae;
a plurality of solid state power amplifiers coupled between the plurality of receive antennae and the plurality of transmit antennae, each of the solid state power amplifiers comprising:
a Doherty amplifier having a main arm, an auxiliary arm, and biasing circuitry configured to independently bias the main arm and the auxiliary arm according to a set of control signals; and
a control circuit configured to receive a specified power output for each of the Doherty amplifiers and provide a corresponding set of control signals to independently bias the main arm and the auxiliary arms according to the specified power output, each of the solid state power amplifiers comprising:
an input port connectable to one or more of the receive antennae;
an output port connectable to one or more of the transmit antennae, wherein the main arm is connected between the input port and the output port and includes a first main amplifier stage configured to generate a first output signal from an input signal received from the input port, and wherein the auxiliary arm is connected in parallel with the main arm between the input port and the output port and includes a first auxiliary amplifier stage configured to generate a second output signal by amplifying portions of the input signal received the input port having an amplitude above a threshold level;
an input splitter configured to receive the input signal and provide it to the main arm and the auxiliary arm;
a combining circuit configured to receive the first output signal and the second output signal, generate therefrom a combined output signal and provide the combined output signal to the output port; and
wherein the biasing circuitry includes:
a first bias control circuit connected to the first main amplifier stage and configured to bias the first main amplifier stage according to a corresponding first set of control signals; and
a second bias control circuit connected to the first auxiliary amplifier stage and configured to bias the first auxiliary amplifier stage according to a corresponding second set of control signals, and
wherein the control circuit is configured to generate the corresponding first set of control signals and the corresponding second sets of control signals, the first set of controls signals configured to generate the first output signal to have the power output over a first output range when the input signal has an amplitude below the threshold level, and the corresponding second set of control signals configured relative to the corresponding first set of control signals to generate the combined output signal to have the specified power output over a second output range when the input signal has an amplitude above the threshold level.
2. The satellite of claim 1 , further comprising:
an input hybrid matrix coupled to multiple ones of the receive antennae; and
an output hybrid matrix coupled to multiple ones of the transmit antennae, wherein the plurality of solid state power amplifiers are coupled between the input hybrid matrix and the output hybrid matrix to amplify signals from the input hybrid matrix as a multiport amplifier.
3. The satellite of claim 1 , further comprising:
a beamforming circuit connected between the plurality of receive antennae and the plurality of solid state power amplifiers, wherein the beamforming circuit is configured generate a plurality of input signals for a corresponding plurality of the solid state power amplifiers to generate an output forming a beam when transmitted from a corresponding plurality of the transmits antennae.
4. The satellite of claim 1 , wherein the control circuit is further configured to receive an updated specified power output for each of the Doherty amplifiers and provide a corresponding updated set of control signals to independently bias the main arm and the auxiliary arms according to the updated specified power output.
5. The satellite of claim 1 , wherein, for each of the solid state power amplifiers:
the main arm comprises a plurality of N serially connected main amplifier stages, including the first main amplifier stage, connected to the input port and configured to generate the first output signal from the input signal;
the auxiliary arm comprises a plurality of N serially connected auxiliary amplifier stages, including the first auxiliary amplifier stage, connected to the input port and configured to generate the second output signal from the input signal;
the first bias control circuit is connected to the N main amplifier stages and configured to individually bias the N main amplifier stages according to the corresponding first set of control signals; and
the second bias control circuit connected to the N auxiliary amplifier stages and configured to individually bias the N auxiliary amplifier stages according to the corresponding second set of control signals.
6. The satellite of claim 1 , wherein the control circuit is configured to change the corresponding first set of control signals and the corresponding second set of control signals in response to the specified power output being changed.
7. The satellite of claim 6 , wherein the changed corresponding first set of control signals and the corresponding second set of control signals change the threshold level.
8. The satellite of claim 1 , wherein further composing:
a memory, where the control circuit determines the corresponding first set of control signals and the corresponding second set of control signals corresponding to the specified response from values stored in the memory.
9. The satellite of claim 1 , wherein the control circuit determines the corresponding first set of control signals and the corresponding second set of control signals corresponding to the specified response by monitoring the combined output signal.
10. The satellite of claim 1 , wherein the first main amplifier stage and the first auxiliary amplifier stage are amplifiers of differing classes.
11. The satellite of claim 1 , wherein the main arm, the auxiliary arm, the input splitter, the combining circuit, first bias control circuit, second bias control circuit and control circuit are formed on a common integrated circuit.
12. The satellite of claim 1 , wherein the input splitter comprises:
a quadrature generator connected to the input port and configured receive the input signal, generate form the input signal a first quadrature signal and a second quadrature signal, and to provide the input signal to the main arm and the auxiliary arm respectively as the first quadrature signal and second quadrature signal.
13. The satellite of claim 1 , wherein the satellite is a communications satellite.