Doherty amplifier and its distortion characteristic compensation method
Pre-distortion compensation circuits ( 11, 12 ) are disposed at stages previous to carrier amplifier 13 and peak amplifier 14 , respectively. Pre-distortion compensation circuit ( 11 ) has such characteristics that compensate carrier amplifier ( 13 ) for a distortion characteristically produced on the operation thereof, particularly, an amplitude-phase (AM-PM) distortion, while pre-distortion compensation circuit ( 12 ) has such characteristics that compensate peak amplifier ( 14 ) for a distortion characteristically produced on the operation thereof, particularly, an AM-PM distortion. Thus, the Doherty amplifier is also compensated for its own AM-PM distortion characteristic to accomplish a low distortion characteristic and implement an ideal power combining operation thereof.
1. A Doherty amplifier having:
a carrier amplifier which is performing a signal amplifying operation at all times irrespective of an input signal level;
a peak amplifier which performs an amplifying operation only when the input signal level increases to a certain level or higher to generate high power;
an output combiner circuit for combining the outputs of said carrier amplifier and said peak amplifier to deliver a combined output; and
an input branching circuit for distributing an input signal to said carrier amplifier and to said peak amplifier,
said Doherty amplifier characterized by comprising:
a first pre-distortion compensation circuit disposed at a stage previous to said carrier amplifier and having such characteristics that compensate said carrier amplifier for a distortion characteristically produced on the operation of said carrier amplifier; and
a second pre-distortion compensation circuit disposed at a stage previous to said peak amplifier and having such characteristics that compensate said peak amplifier for a distortion characteristically produced on the operation of said peak amplifier.
2. The Doherty amplifier according to claim 1 , wherein the distortion compensated for by said first and second pre-distortion compensation circuits is an amplitude-phase distortion.
3. A method of compensating a Doherty amplifier for a distortion characteristic, said Doherty amplifier having a carrier amplifier which is performing a signal amplifying operation at all times irrespective of an input signal level, a peak amplifier which performs an amplifying operation only when the input signal level increases to a certain level or higher to generate high power, an output combiner circuit for combining the outputs of said carrier amplifier and said peak amplifier to deliver a combined output, and an input branching circuit for distributing an input signal to said carrier amplifier and to said peak amplifier, said method comprising the steps of:
distributing an input signal to said carrier amplifier and to said peak amplifier by said input branching circuit;
compensating a signal distributed to said carrier amplifier by said input branching circuit for a distortion characteristically produced on the operation of said carrier amplifier;
compensating a signal distributed to said peak amplifier by said input branching circuit for a distortion characteristically produced on the operation of said peak amplifier;
amplifying the signal by said carrier amplifier after the signal has been compensated for the distortion characteristically produced on the operation of said carrier amplifier;
amplifying the signal by said peak amplifier after the signal has been compensated for the distortion characteristically produced on the operation of said peak amplifier; and
combining the outputs of said carrier amplifier and said peak amplifier to deliver a combined output.
4. The method of compensating a Doherty amplifier for a distortion characteristic according to claim 3 , wherein the distortion characteristically produced on the operation of said carrier amplifier and the distortion characteristically produced on the operation of said peak amplifier are amplitude-phase distortions.