Power amplifier suppressing radiation of second harmonic over wide frequency band
Two trap circuits different in frequencies at which short-circuit is established are provided in an output matching circuit. Out of the two trap circuits, the trap circuit higher in frequency at which short-circuit is established is arranged closer to a power amplification element. Thus, a frequency band higher than a frequency twice as high as a central frequency of a transmission frequency band is trapped, impedance of the output matching circuit with respect to the frequency in a frequency band twice as high as the transmission frequency band on the side of an output end of the power amplification element is kept in a state close to short-circuit, and the trap circuit lower in frequency at which short-circuit is established traps the frequency band lower than the frequency twice as high as the central frequency of the transmission frequency band.
1. A power amplifier comprising:
a power amplification element; and
an output matching circuit connected to an output end of said power amplification element; wherein
said output matching circuit includes a plurality of trap circuits establishing short-circuit at frequencies higher than a desired transmission frequency band and at frequencies different from each other,
out of at least two trap circuits among said plurality of trap circuits, the trap circuit higher in frequency at which short-circuit is established is arranged closer to the output end of said power amplification element than the trap circuit lower in frequency at which short-circuit is established,
the trap circuit arranged closer to the output end of said power amplification element is set such that a frequency at which short-circuit is established is more than twice as high as a central frequency of said desired transmission frequency band and impedance of said output matching circuit on a side of the output end of said power amplification element is substantially short-circuited with respect to at least one frequency in a frequency band twice as high as said desired transmission frequency band, and
the trap circuit lowest in frequency at which short-circuit is established among said trap circuits is set such that a frequency at which short-circuit is established is at least 1.4 times as high as a frequency highest in said desired transmission frequency band and less than twice as high as the central frequency of said desired transmission frequency band.
2. The power amplifier according to claim 1 , wherein
the trap circuit arranged closer to the output end of said power amplification element is arranged closest to the output end of said power amplification element.
3. The power amplifier according to claim 1 , wherein
the frequency at which the trap circuit establishes short-circuit, the trap circuit being arranged closer to the output end of said power amplification element, is set to a frequency in a frequency band three times as high as said desired transmission frequency band.
4. The power amplifier according to claim 1 , wherein
said trap circuit is implemented by a series resonant circuit including at least an inductor and a capacitor.