Patent ID: 8198938

Claim:
A broadband Doherty power amplifier performing two-stage output matching, the amplifier comprising: a carrier amplifier; a peaking amplifier; a first quarter wave transformer connected to an output terminal of the carrier amplifier; a second quarter wave transformer connected to an output terminal of the peaking amplifier; and an output matching circuit connected to rear ends of the first quarter wave transformer and the second quarter wave transformer, wherein a front end of at least the first quarter wave transformer is directly connected only to the output terminal of the carrier amplifier and the rear end of the first quarter wave transformer is directly connected to the output matching circuit, wherein the first quarter wave transformer and the second quarter wave transformer are connected in parallel to each other and cause a Doherty operation while serving as a first stage of the two-stage output matching, wherein the output matching circuit serves as a second stage of the two-stage output matching, wherein the first quarter wave transformer performs the output matching such that the load line impedance R out of the carrier amplifier is matched to an optimum power source impedance R opt of the carrier amplifier, and the second quarter wave transformer performs the output matching such that the load line impedance R out ′ of the peaking amplifier is matched to an optimum power source impedance R opt ′ of the peaking amplifier, the first quarter wave transformer having characteristic impedance R o satisfying the condition of R opt <R o <R out or R opt >R o >R out and the second quarter wave transformer having characteristic impedance R o ′ satisfying the condition of R opt ′<R o ′<R out ′ or R opt ′>R o ′>R out ′, and wherein the output matching circuit matches a load impedance to R out //R out ′ ( where ⁢ ⁢ R out // R out ′ = R out × R out ′ R out + R out ′ ) .