Power amplification apparatus, OFDM modulation apparatus, wireless transmission apparatus, and distortion reduction method for power amplification apparatus

1. A power amplification apparatus comprising:

an inverse fast Fourier transform section configured to perform an inverse fast Fourier transformation on data allocated to a plurality of sub-carriers;

a parallel/serial conversion section configured to output time-domain data received in parallel from the inverse fast Fourier transform section as a time-domain analog signal including a real-part time-domain analog signal and an imaginary-part time-domain analog signal;

a power amplifier configured to perform a power amplification on the time-domain analog signal, wherein a saturation output level of the power amplifier is adjustable in accordance with a switching signal;

a real-part comparator configured to compare an amplitude of a signal in each time slot of the real-part time-domain analog signal with a predetermined threshold, and

an imaginary-part comparator configured to compare an amplitude of a signal in each time slot of the imaginary-part time-domain analog signal with the predetermined threshold, wherein

the saturation output level of the power amplifier is switched based on outputs of the real-part comparator and the imaginary-part comparator.

2. The power amplification apparatus of claim 1 , further comprising:

a logical sum circuit configured to calculate a logical sum of the outputs of the real-part comparator and the imaginary-part comparator.

3. The power amplification apparatus of claim 2 , wherein the saturation output level of the power amplifier is switched based on an output of the logical sum circuit.

4. The power amplification apparatus of claim 2 , further comprising:

a detection section configured to detect an output power of the power amplifier.

5. The power amplification apparatus of claim 4 , further comprising:

a wave detection circuit configured to compare the detected output power of the power amplifier with a predetermined value.

6. The power amplification apparatus of claim 5 , further comprising:

a logical product circuit configured to calculate a logical product of an output of the logical sum circuit and the wave detection circuit.

7. The power amplification apparatus of claim 6 , wherein the saturation output level of the power amplifier is switched based on an output of the logical product circuit.

8. The power amplification apparatus of claim 5 , further comprising:

a threshold change section configured to variably set the predetermined threshold based on an output of the wave detection circuit.

9. The power amplification apparatus of claim 8 , wherein the output of the wave detection circuit is an analog signal.

10. The power amplification apparatus of claim 9 , wherein the threshold change section includes an analog/digital converter configured to convert the output of the wave detection circuit into a digital signal, which is used to set the predetermined threshold.

11. A power amplification method comprising:

performing an inverse fast Fourier transformation on data allocated to a plurality of sub-carriers;

outputting time-domain data received in parallel from the inverse fast Fourier transformation as a time-domain analog signal including a real-part time-domain analog signal and an imaginary-part time-domain analog signal;

performing a power amplification on the time-domain analog signal, wherein a saturation output level of the power amplification is adjustable in accordance with a switching signal;

comparing an amplitude of a signal in each time slot of the real-part time-domain analog signal with a predetermined threshold;

comparing an amplitude of a signal in each time slot of the imaginary-part time-domain analog signal with the predetermined threshold; and

calculating a logical sum of outputs of the real-part comparing and the imaginary-part comparing, wherein

the saturation output level of the power amplification is switched based on the calculated logical sum.

12. The power amplification method of claim 11 , further comprising:

detecting an output power of the power amplification.

13. The power amplification method of claim 12 , further comprising:

variably setting the predetermined threshold of the real-part comparing and the imaginary-part comparing based on the detected output power of the power amplification.

14. A power amplification method comprising:

performing an inverse fast Fourier transformation on data allocated to a plurality of sub-carriers;

outputting time-domain data received in parallel from the inverse fast Fourier transformation as a time-domain analog signal including a real-part time-domain analog signal and an imaginary-part time-domain analog signal;

performing a power amplification on the time-domain analog signal, wherein a saturation output level of the power amplification is adjustable in accordance with a switching signal;

comparing an amplitude of a signal in each time slot of the real-part time-domain analog signal with a predetermined threshold;

comparing an amplitude of a signal in each time slot of the imaginary-part time-domain analog signal with the predetermined threshold;

calculating a logical sum of outputs of the real-part comparing and the imaginary-part comparing,

detecting an output power of the power amplification;

comparing the detected output power of the power amplification with a predetermined value; and

calculating a logical product of the calculated logical sum and a result of comparing the detected output power of the power amplification with a predetermined value, wherein

the saturation output level of the power amplification is switched based on an output of the calculated logical product.

15. An orthogonal frequency-division multiplexing modulation apparatus comprising:

an inverse fast Fourier transform section configured to perform an inverse fast Fourier transformation on data allocated to a plurality of sub-carriers;

a parallel/serial conversion section configured to output time-domain data received in parallel from the inverse fast Fourier transform section as a time-domain analog signal including a real-part time-domain analog signal and an imaginary-part time-domain analog signal;

a power amplifier configured to perform a power amplification on the time-domain analog signal, wherein a saturation output level of the power amplifier is adjustable in accordance with a switching signal;

a real-part comparator configured to compare an amplitude of a signal in each time slot of the real-part time-domain analog signal with a predetermined threshold;

an imaginary-part comparator configured to compare an amplitude of a signal in each time slot of the imaginary-part time-domain analog signal with the predetermined threshold, wherein

the saturation output level of the power amplifier is switched based on outputs of the real-part comparator and the imaginary-part comparator.

16. A wireless transmission apparatus comprising:

an inverse fast Fourier transform section configured to perform an inverse fast Fourier transformation on data allocated to a plurality of sub-carriers;

a parallel/serial conversion section configured to output time-domain data received in parallel from the inverse fast Fourier transform section as a time-domain analog signal including a real-part time-domain analog signal and an imaginary-part time-domain analog signal;

a power amplifier configured to perform a power amplification on the time-domain analog signal, wherein a saturation output level of the power amplifier is adjustable in accordance with a switching signal;

a real-part comparator configured to compare an amplitude of a signal in each time slot of the real-part time-domain analog signal with a predetermined threshold;

an imaginary-part comparator configured to compare an amplitude of a signal in each time slot of the imaginary-part time-domain analog signal with the predetermined threshold, wherein

the saturation output level of the power amplifier is switched based on outputs of the real-part comparator and the imaginary-part comparator.