Patent ID: 8593219

Claim:
A radio frequency (RF) amplifier structure comprising: a signal splitter that is configured to receive an RF input signal and produce a plurality of RF signals based on the RF input signal; a first RF amplifier stage having a first RF amplifier device coupled to a first output impedance transforming circuit, wherein the first RF amplifier stage is configured to receive a first RF signal of the plurality of RF signals and produce a first amplified RF signal based on the first RF signal; a second RF amplifier stage having a second RF amplifier device coupled to a second output impedance transforming network, wherein the second RF amplifier stage is configured to receive a second RF signal of the plurality of RF signals and produce a second amplified RF signal based on the second RF signal; a power combiner that is configured to combine the first amplified RF signal and the second amplified RF signal to produce an output signal; an output matching impedance transform circuit coupled between an output of the first amplifier device and the power combiner, wherein the output matching impedance transform circuit comprises a low pass multiple section inductance-capacitance circuit and provides impedance matching between the output of the first amplifier device and the power combiner, wherein the output matching impedance transform circuit has approximately an odd multiple of 90 electrical degrees over the RF amplifier structure's frequency range of operation in order to enable impedance inversion between the power combiner and the output of the first amplifier device such that an impedance presented by the output impedance transform circuit to the first amplifier device will be load modulated between a highly efficient power saturating impedance when the second amplifier device is in cutoff and a non-power saturating impedance which delivers high power to the power combiner when the second amplifier device is biased on; an adjustable phase delay circuit succeeding the second RF amplifier device that receives the second amplified RF signal and routes the second amplified RF signal to the power combiner; and wherein a phase delay and a reactance of the adjustable phase delay circuit is controllably adjusted based on a frequency of the RF input signal and minimizes a flow of power from the power combiner back into the output of the second amplifier device when the second amplifier device is in cutoff while allowing power flow from the second amplifier device to the power combiner when the second amplifier device is biased on.