Pulse area modulation and high-efficiency linear power amplifier system using the same

1. A pulse area modulation method for amplifying an input signal, whose values are f(t 1 ), f(t 2 ), . . . f(t 2 ) at times t 1 , t 2 , . . . t n , respectively, at which the input signal is sampled for a pulse modulation, the values of the input signal having a characteristic that if the input signal were modulated by the pulse width modulation (PWM), the pulse width modulated signal would have a waveform with a height of 1 and with widths of x 1 , x 2 , . . . x n , wherein x k is proportional to f(t k ) (1<=k<=n),

wherein in case the values of the input signal having a minimum value of m and a maximum value of M are partitioned by threshold values Th 1 , Th 2 , . . . Th n−1 , while an inequality: m<Th 1 <Th 2 <. . . <Th n— <M is satisfied,

if the value of the input signal at tk satisfies an inequality: f(t k )<=Th 1 , the modulated input signal by the pulse area modulation method has a waveform with a height of H 1 and with a width of x 1 *H 1 ,

if the value of the input signal at tk satisfies an inequality: Th q−1 <f(t k )<=Th q , the modulated input signal by the pulse area modulation method has a waveform with a height of 1/H q and with a width of x q *H q , and

if the value of the input signal at t k satisfies an inequality: f(t k )>Th n−1 , the modulated input signal by the pulse area modulation method has a waveform with a height of 1/H n and with a width of x n *H n ,

wherein 1<=H n <H n−1 < . . . <H 1 and 2<=q<=n−1.

2. The pulse area modulation method of claim 1 , wherein a switching period t a −t a−1 (2<=a <=n) are not constant.

3. The pulse area modulation method of claim 1 , wherein the width of the modulated pulse (the modulated input signal) satisfies an inequality:x a−1 *H a−1 <=t a −t a−1 (2<=a <=n).

4. The pulse area modulation method of claim 1 , wherein the H n is 1.

5. The pulse area modulation method of claim 1 , wherein intervals between adjacent threshold values (Th b −Th b−1 for 2<=b<=n−1) are constant.

6. The pulse area modulation method of claim 1 , wherein intervals between adjacent heights (1/H a −1/H a−1 for 2<=a <=n) are constant.

7. The pulse area modulation method of claim 1 , wherein the modulated input signal by the pulse area modulation method has a height of 0 except sections where the heights and the widths thereof are 1/H k , x k *H k respectively.

8. A pulse area modulation method for amplifying an input signal i(t) which is fed to a power amplifier system, comprising the steps of:

modulating the input signal i(t) such that an area of a modulated signal i M (t) is proportional to an amplitude of the input signal i(t);

amplifying the modulated signal i M (t),wherein the area of the modulated signal i M (t) is determined by an area between a t-axis (a time axis) and the waveform of the modulated signal i m (t); and

wherein an amplitude of the modulated signal i M (t) is determined as one of N predetermined amplitude levels by comparing the amplitude of the input signal i(t) with N−1 threshold values.

9. The pulse area modulation method of claim 8 , wherein the input signal i(t) is an envelop signal.

10. A high-efficiency linear power amplifier system using the pulse area modulation comprising:

an envelop/phase decomposer 502 for decomposing an input signal 501 into an envelop signal 508 and a phase signal 509 ;

a pulse area modulator 503 for modulating the decomposed envelop signal 508 such that an area (multiplication of a pulse height and a pulse width) of the modulated envelop signal is proportional to an amplitude of the envelop signal 508 ;

a control signal generator 504 for converting the modulated envelop signal into a control signal 510 ;

an automatic gain adjuster 512 for equalizing the pulse height of the modulated envelop signal while maintaining the pulse width to be equal that of the modulated envelop signal;

a mixer 511 for mixing the decomposed phase signal 509 with the output of the automatic gain adjustor 512 to produce a RF pulse train 513 having a pulse width which is identical to that of the modulated envelop signal;

a power amplifier 505 for amplifying the RF pulse train 513 , while an output level thereof is controlled by the control signal 510 , to generate an amplified RF pulse train; and

a band pass filter 506 for restoring the original input signal 501 from the amplified RF pulse train.

11. The high-efficiency linear power amplifier system of claim 10 , wherein a pulse width of the RF pulse train 513 is equal to that of the modulated envelop signal and a height of the RF pulse train 513 is constant regardless of the input signal 501 .

12. The high-efficiency linear power amplifier system of claim 10 , wherein the output of the power amplifier 505 is discretely controlled according to the control signal 510 .

13. The high-efficiency linear power amplifier system of claim 10 , wherein the power amplifier 505 includes a plurality of small-sized power amplifiers 601 1 ˜ 601 N which are connected in parallel, and

wherein the output level of the power amplifier 505 is controlled by switching on or switching off the respective small-sized power amplifiers 601 1 ˜ 601 N by the control signal 510 .

14. The high-efficiency linear power amplifier system of claim 10 , wherein the power amplifier 505 is a switch mode power amplifier.

15. The high-efficiency linear power amplifier system of claim 13 , wherein output capacities of the small-sized power amplifiers 601 1 ˜ 601 N are different.

16. The high-efficiency linear power amplifier system of claim 10 , wherein the power amplifier 505 includes a plurality of small-sized transistors 701 1 ˜ 701 N which are connected in parallel,

wherein respective λ/4 (λ is a wavelength of a carrier frequency) transmission lines 703 1 ˜ 703 N are connected to each output port of the small-sized transistors,

wherein a harmonic short circuit 704 and a load 705 are connected in parallel between the output ports of the λ/4 transmission lines and a ground(GND), and

wherein the output level of the power amplifier 505 is controlled by switching on or off the small-sized transistors 701 1 ˜ 701 N respectively by the control signal 510 .

17. The high-efficiency linear power amplifier system of claim 16 , wherein the harmonic short circuit 704 is a parallel LC resonance circuit.

18. The high-efficiency linear power amplifier system of claim 16 , wherein RF switches 707 1 ˜ 707 N are connected between the output ports of the small-sized transistors and the GND, and

wherein the small-sized transistors are switched on or off by applying the control signal 510 thereto.