Switched modulation of a radio-frequency amplifier

1. A method of switch-modulating a radio-frequency power amplifier, wherein an input signal into the power amplifier is represented by an I-signal and Q-signal of complex components (I+j·Q), the method comprising:

sampling and pulse width modulating the I-signal and the Q-signal separately to generate a modulated I-signal pulse sequence and a modulated Q-signal pulse sequence;

time shifting the pulses corresponding to negative sample values relative to the pulses corresponding to positive sample values; and

delaying each pulse of the I-signal pulse sequence by introducing a delaying time shift.

2. The method of claim 1 further comprising interpolating new samples values to be mapped on the time shifted pulses.

3. The method of claim 1 further comprising:

power amplifying the I-signal pulse sequence and the Q-signal pulse sequence separately;

combining the amplified I-signal pulse sequence and the amplified Q-signal pulse sequence; and

filtering the amplified and combined pulse sequences to generate a correct output signal.

4. The method of claim 1 wherein pulse width modulating the I-signal and the Q-signal separately comprises mapping a sample amplitude on the width of a pulse of one of the pulse sequences.

5. The method of claim 4 wherein the sample amplitude is corrected to obtain a linear function.

6. The method of claim 1 wherein the delaying time shift in the I-branch is 0.25 of a sampling interval T s , and corresponds to a 90-degree phase shift.

7. The method of claim 1 wherein time shifting the negative sample pulses relative to the positive sample pulses comprises placing the negative sample pulses in a second half of a sampling interval T s , and placing the positive sampling pulses in a first half of the sampling interval T s .

8. The method of claim 2 wherein interpolating new sample values comprises a linear interpolation between two adjacent samples.

9. The method of claim 2 wherein interpolating new sample values involves cubic spline interpolation.

10. A circuit for switch-modulating a radio-frequency power amplifier by separately modulating an I-signal and a Q-signal of complex components (I+j·Q) of an input signal, the circuit comprising:

one or more pulse width modulators configured to sample and modulate an I-signal and a Q-signal separately to generate a modulated I-signal pulse sequence and a modulated Q-signal pulse sequence;

a time shifter configured to displace, within a sampling interval, those generated pulses that correspond to negative sample values relative to those generated pulses that correspond to positive sample values; and

a delay unit configured to introduce a delaying time shift in the I-signal pulse sequence.

11. The circuit of claim 10 further comprising an interpolator configured to interpolate new sample amplitudes to be mapped on a width of each time shifted pulse.

12. The circuit of claim 10 further comprising:

two power amplifiers configured to amplify the I-signal pulse sequence and the Q-signal pulse sequence separately;

a combiner configured to combine the amplified I-signal pulse sequence with the amplified Q-signal pulse sequence; and

a filter configured to band-pass filter the combined pulse sequences to generate a correct amplified output signal.

13. The circuit of claim 10 wherein each said pulse width modulator is configured to map the sample amplitude onto the width of a pulse.

14. The circuit of claim 13 further comprising a correcting calculator configured to obtain a linear relationship between a width of the pulse and a sample amplitude.

15. The circuit of claim 10 wherein said delaying time shift is 0.25 of a sampling interval T s , and corresponds to a 90-degree phase shift of the modulated I-signal pulse sequence.

16. The circuit of claim 11 wherein said interpolator comprises a cubic spline interpolator.

17. The circuit of claim 10 wherein the power amplifier is one of a Class D amplifier and a Class E amplifier.

18. The circuit of claim 11 wherein said interpolator comprises a linear interpolator.