CPC H03F 1/56 (2013.01) [H03F 3/26 (2013.01); H04B 1/401 (2013.01); H03F 2200/387 (2013.01); H03F 2200/451 (2013.01); H03F 2200/48 (2013.01); H03F 2200/534 (2013.01); H03F 2200/537 (2013.01); H03F 2200/541 (2013.01)] | 10 Claims |
1. A push-pull power amplifier system having an input, an output, and a variable load-line impedance comprising:
an input amplifier coupled to the input of the push-pull power amplifier system to receive an unbalanced radio frequency (RF) input signal and provide an unbalanced amplified RF signal at an output of the input amplifier;
an input transformer having a primary winding coupled to the output of the input amplifier and having a secondary winding to provide a pair of balanced RF signals based on the unbalanced amplified RF signal;
a pair of complementary amplifiers to receive a respective balanced RF signal of the pair of balanced RF signals and provide a pair of amplified balanced RF signals;
an output transformer having a primary winding to receive a respective amplified balanced RF signal of the pair of amplified balanced RF signals and a secondary winding to provide an unbalanced amplified RF output signal on a load-line coupled to the output of the push-pull power amplifier system;
a switchable shunt capacitance switchably connected between the load-line and a reference potential; and
a switch configured to selectively connect the switchable shunt capacitance to the reference potential and disconnect the switchable shunt capacitance from the reference potential to vary an impedance of the load-line to match an impedance at the primary winding of the output transformer.
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