Power amplifying apparatus and radio communications apparatus using same
By extracting a portion of RF signals from an input side of a multistage RF amplifier with a detector, and converting extracted signals into envelope signals, low-frequency second-harmonic distortion components are efficiently extracted. Then, the extracted low-frequency second-harmonic distortion components are amplified with a low-frequency amplifier, and phase adjusted with a phase shifter, after which they are injected into a gate or base bias of the final stage of the multistage RF amplifier. As a result, the low-frequency second-harmonic distortion components are converted into third-harmonic distortion due to the non-linearity of transistors, and the third-harmonic distortion thus obtained cancels out the third-harmonic distortion originally present in the multistage RF amplifier.
1. A power amplifying apparatus, comprising:
RF amplifying means including a plurality of transistor stages;
envelope curve computing means for computing a digital envelope signal from two chrominance signals in a digital baseband section;
a D/A converter for converting a digital envelope signal outputted from said envelope curve computing means into an analog signal; and
means for injecting an analog envelope signal outputted by said D/A converter into one of a gate and base bias of a final stage of said RF amplifying means.
2. The power amplifying apparatus according to claim 1 , wherein said digital baseband section includes a low-frequency amplifier for amplifying a digital envelope signal outputted by said envelope curve computing means.
3. The power amplifying apparatus according to claim 1 , wherein said digital baseband section includes a phase shifter for adjusting a phase of a digital envelope signal outputted by said envelope curve computing means.
4. The power amplifying apparatus according to claim 1 , wherein said digital baseband section includes an envelope curve computing means whose output is inputted to a filter for blocking a harmonic component included in a digital envelope signal outputted by said envelope curve computing means.
5. A radio communications apparatus with a power amplifying apparatus as a power amplifier configuring a front-end of a transmission system, said power amplifying apparatus comprising:
RF amplifying means including a plurality of transistor stages;
envelope curve computing means for computing a digital envelope signal from two chrominance signals in a digital baseband section;
a D/A converter for converting a digital envelope signal outputted by said envelope curve computing means into an analog signal; and
a bias circuit for injecting an analog envelope signal outputted by said D/A converter into one of a gate and base bias of a final stage in said RF amplifying means.