Abstract:
An apparatus and method amplifies a delta-sigma modulated signal and delivers the amplified signal to a power amplifier without distortion in a communication system. The apparatus receives a delta-sigma modulated signal, phase-delays the received delta-sigma modulated signal by a multiple of 360° for a bandwidth of the delta-sigma modulated basic signal, and amplifies the phase-delayed signal, facilitating implementation of a high-efficiency delta-sigma modulation-based amplification system.

Description:
PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. § 119(a) of an application entitled “Input Matching Apparatus and Method for Power Amplifier Using Delta-Sigma Modulated Signal” filed in the Korean Intellectual Property Office on Jul. 15, 2005 and assigned Serial No. 2005-64342, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to an amplification system for mobile communication, applied to a communication system, and in particular, to a Class-S amplifier system for efficiently amplifying a signal having a high Peak to Average Power Ratio (PAPR) in a communication system.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, power amplifiers used in a communication system are identified according to their classes, and the classes are defined in light of operation duration and a bias current of an output device. In that light, power amplifiers are classified as Class A, Class B, Class C, Class AB, Class F, and Class S. Each of the classes of the power amplifiers will be described in brief hereinbelow. A power amplifier whose operating point is put on the center of the bias is classified as Class A, and a power amplifier whose operating point is put on a 0V (zero volt)-bias is classified as Class B. A power amplifier whose operating point is put between Class A and Class B is classified as Class AB, and a power amplifier in which harmonic matching is added to an output matching stage is classified as Class F. Finally, a power amplifier that amplifies an input pulse signal in the form of a pulse is classified as Class S.  
         [0006]     Herein, a description will be made of a Class-S system among the amplification systems of the various classes, and a Class-S amplifier used in the Class-S system.  
         [0007]     The Class-S amplifier system converts a Radio Frequency (RF) signal into an RF pulse signal using a delta-sigma modulator. The delta-sigma modulated signal is amplified into an RF pulse signal using a power amplifier operating in a switching mode. Subsequently, the amplified signal is restored to its original signal after a switching harmonic component is removed therefrom through a band-pass filter. In this case, the power amplifier, as it operates in the switching mode, theoretically has an efficiency of 100%. In addition, a nonlinear component generated by the delta-sigma modulator and the RF amplifier is removed through a separate linearizer.  
         [0008]     With reference to  FIG. 1 , a detailed description will now be made of a structure of the Class-S amplification system.  
         [0009]      FIG. 1  is a block diagram schematically illustrating a structure of a Class-S system using a general band-pass delta-sigma modulator.  
         [0010]     Referring to  FIG. 1 , the general Class-S system includes a delta-sigma modulator  101 , and a Class-S amplifier  107  composed of a power amplifier  103 , and a band-pass filter  105 .  
         [0011]     The delta-sigma modulator  101  converts an input RF signal into an RF pulse signal using delta-sigma modulation, and outputs the RF pulse signal to the power amplifier  103 . The power amplifier  103  operating in the switching mode amplifies the RF pulse signal received from the delta-sigma modulator  101  to a required level set in the system, and outputs the amplified RF pulse signal to the band-pass filter  105 . The band-pass filter  105  removes a switching harmonic component included in the received amplified RF pulse signal to restore the RF pulse signal to its original signal. In this case, the power amplifier  103 , as it operates in the switching mode, theoretically has an efficiency of 100%. Although not illustrated in the drawing, the Class-S system can include a separate linearizer for removing a nonlinear component generated by the delta-sigma modulator  101  and the power amplifier  103 .  
         [0012]     In order to generate the RF pulse signal, the conventional amplification system uses an over-sampling Analog-to-Digital Converter (ADC) such as the band-pass delta-sigma modulator. However, in the common mobile communication system, an RF signal has a frequency of 800 MHz or higher. Therefore, the conventional amplification system undesirably needs a band-pass delta-sigma modulator of  4 -times over-sampling, i.e. over-sampling of about 3.2 GHz. For example, for a band of the IMT-2000 communication system, there is need for a fast band-pass delta-sigma modulator of about 8 GHz or higher.  
         [0013]     In addition, the switching-mode power amplifier  103  should undesirably operate at up to 5 times the input RF frequency, i.e. have a broadband characteristic, for accurate amplification of the RF pulse signal output from the delta-sigma modulator  101 . In other words, for a band of the IMT-2000 system, there is a need for a switching-mode power amplifier operating at about 10 GHz. However, it is difficult to actually implement the fast band-pass delta-sigma modulator and the switching-mode power amplifier, and they are expensive. In addition, it is also hard to actually implement a method of matching an input impedance of the power amplifier for the broadband input signal.  
         [0014]     Aside from the block diagram of the power amplification system using the delta-sigma modulator,  FIG. 1  shows signal flow diagrams generated at outputs of respective blocks, i.e. shows a signal flow in frequency and time domains.  
         [0015]     As illustrated in  FIG. 1 , the delta-sigma modulator  101  converts a random input signal into a Pulse Width Modulation (PWM) signal having a constant envelope, generating quantization noises at an outer band of the signal. The power amplifier  103  amplifies the intact delta-sigma modulated signal at high efficiency. The power amplifier  103  performs linear amplification on the output signal of the delta-sigma modulator  101 , having the constant envelope. To achieve high efficiency, the power amplifier  103  may be a Class-F amplifier.  
         [0016]     Ideally, the Class-F amplifier has an efficiency of 100%. Therefore, the band-pass filter  105  receives the output signal of the power amplifier  103 , and suppresses noises at the outer band of the signal to extract only the amplified original signal. One of the most important considerations in the amplification system is to deliver the delta-sigma modulated broadband signal to the power amplifier without distortion.  
         [0017]     In order to increase a Signal-to-Noise Ratio (SNR), the conventional Class-S system using the delta-sigma modulator converts, in the time domain, a pulse wave into a signal having a bandwidth much broader than that of the original signal in the frequency band using an over-sampling technique and a noise shaping technique. In this case, if a baseband delta-sigma modulator is used, the broadband signal should be delivered from a digital Intermediate Frequency (IF) stage to the power amplifier via an RF transceiver without distortion. In addition, if the band-pass delta-sigma modulator is used, the broadband signal should be delivered from an output of the delta-sigma modulator to the power amplifier without distortion.  
         [0018]     Although there is a theoretical description of a method for delivering transmission signals to the power amplifier without distortion, the conventional Class-S system does not present a detailed implementation method thereof and the possible problems occurring when actually implemented. That is, although implementation of the delta-sigma modulator and the power amplifier is possible, there is no proposed solution for combining them and reducing distortion of the signals delivered to the power amplifier.  
         [0019]     That is, the conventional amplification system using the delta-sigma modulator has no scheme capable of delivering the delta-sigma modulated constant envelope signal to the power amplifier without distortion. Therefore, the power amplifier receives a signal not having a constant envelope. As a result, the power amplifier decreases in efficiency, for linear power amplification, causing deterioration of the entire performance of the delta-sigma modulation system.  
       SUMMARY OF THE INVENTION  
       [0020]     It is, therefore, an object of the present invention to provide an apparatus and method capable of applying a delta-sigma modulator to an amplifier system for communication.  
         [0021]     It is another object of the present invention to provide an apparatus and method capable of delivering a signal having a broad bandwidth due to delta-sigma modulation to a power amplifier without distortion.  
         [0022]     It is further another object of the present invention to provide an apparatus and method for generating a signal having a constant envelope using a delta-sigma modulator in a communication system.  
         [0023]     It is yet another object of the present invention to provide an apparatus and method capable of improving performance of a power amplifier by applying a signal having a constant envelope to an amplification system for communication.  
         [0024]     It is still another object of the present invention to provide an apparatus and method capable of providing a high-efficiency power amplification system by delivering an output signal of a delta-sigma modulator to a power amplifier without distortion in a communication system.  
         [0025]     According to one aspect of the present invention, there is provided an apparatus for power amplification in a communication system. The apparatus includes a power amplifier for receiving a delta-sigma modulated signal, and amplifying the delta-sigma modulated signal after a predetermined phase delay.  
         [0026]     According to another aspect of the present invention, there is provided a method for power amplification in a communication system. The method includes receiving a delta-sigma modulated signal; phase-delaying the delta-sigma modulated signal; and power-amplifying the phase-delayed signal.  
         [0027]     According to further another aspect of the present invention, there is provided an apparatus for power amplification in a communication system. The apparatus includes a phase compensation circuit for receiving a delta-sigma modulated signal, and applying a first phase delay to the delta-sigma modulated signal; and an input matching circuit for receiving the first phase delay-applied signal, and applying a second phase delay to the first phase delay-applied signal to output a signal for power amplification.  
         [0028]     According to yet another aspect of the present invention, there is provided a method for power amplification in a communication system. The method includes receiving a delta-sigma modulated signal; applying a first phase delay to the delta-sigma modulated signal; and applying a second delay to the first phase delay-applied signal and amplifying the second phase delay-applied signal. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:  
         [0030]      FIG. 1  is a block diagram schematically illustrating a structure of a Class-S system using a general band-pass delta-sigma modulator;  
         [0031]      FIG. 2  is a diagram schematically illustrating an input matching structure of a power amplification system according to the present invention; and  
         [0032]      FIGS. 3A  to  3 C are diagrams illustrating frequency and time domain characteristics of an input signal to a power amplifier based on a phase delay in a power amplification system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0033]     Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness.  
         [0034]     The present invention provides a Class-S amplifier system including a delta-sigma modulator, a power amplifier operating in a switching mode, and a band-pass filter for recovering an original signal, to efficiently amplify a signal having a high Peak to Average Power Ratio (PAPR).  
         [0035]     In particular, the present invention provides an input matching scheme capable of delivering a signal delta-sigma modulated by a delta-sigma modulator to a power amplifier without distortion, by additionally constructing a phase compensation circuit like an aliasing line for preventing an aliasing effect, along with broadband input matching in the Class-S amplifier system.  
         [0036]     With reference to  FIG. 2 , a description will now be made of an exemplary scheme for designing a high-efficiency amplification system using a delta-sigma modulator.  FIG. 2  is a diagram schematically illustrating an input matching structure of a power amplification system according to the present invention.  
         [0037]     Referring to  FIG. 2 , the amplification system according to the present invention includes a source device  201 , a phase compensation circuit  203 , and a power amplifier  205 . The power amplifier  205  includes an input matching circuit  207  and a transistor  209 . The source device  201  may also be constructed in the delta-sigma modulator  101  shown in  FIG. 1 .  
         [0038]     The present invention, shown in  FIG. 2 , shows a structure for an input matching method in which the source device  201  receives the signal delta-sigma modulated by the delta-sigma modulator  101  of  FIG. 1 , and delivers the input signal to an input node of the transistor  209  in the power amplifier  205  without distortion.  
         [0039]     The overall signal flow shown in  FIG. 2  is equal to that of  FIG. 1 . However, the conventional technology of  FIG. 1  cannot present the combining condition of the delta-sigma modulator  101  and the power amplifier  103  for implementing the signal flow proposed in the present invention. Therefore, the present invention provides a structure capable of delivering an output of the delta-sigma modulator, i.e. an output of the source device  201 , to the power amplifier  205  without distortion as shown in  FIG. 2 .  
         [0040]     As illustrated in  FIG. 2 , the amplification system according to the present invention includes the broadband input matching circuit  207  to deliver the signal delta-sigma modulated by the delta-sigma modulator to an input node of the transistor  209  in the power amplifier  205  without distortion. In addition, the present invention includes the phase compensation circuit  203  together with the input matching circuit  207 . That is, the interference between the basic signal and the harmonic signal due to the delta-sigma modulation may cause an aliasing effect that distorts the original constant envelope signal. In order to solve this problem, the present invention additionally includes the phase compensation circuit  203  having a specific length. In other words, the phase compensation circuit  203  is additionally inserted to remove the aliasing due to a phase delay, and can be implemented with one transmission line. Commonly, the power amplifier receiving the general narrowband signal as an input signal has no need to take the phase delay into account, so the phase delay of the input matching circuit  207  is irrespective of its performance. However, when the amplification system using the delta-sigma modulator receives the broadband signal such as the delta-sigma modulated signal, as its input signal, it should take the phase delay into account in order to avoid distortion of the signal.  
         [0041]     Therefore, because the phase delay of the input matching circuit  207  is not restricted to a particular value, it is necessary to construct the phase compensation circuit  203  for achieving a particular phase delay. That is, the phase compensation circuit  203  of the present invention performs the above function.  
         [0042]     Although the present invention uses an aliasing line as the phase compensation circuit  203  by way of example, it can also use other transmission lines such as a coaxial line or a micro-strip line instead of the aliasing line. Alternatively, the phase compensation circuit  203  can be equivalently replaced by a lumped component as well as the transmission line.  
         [0043]     Alternatively, it is also possible to design the input matching circuit  207  at the initial design stage such that it has a particular phase delay, without separately constructing the phase compensation circuit  203  such as the aliasing line. In this case, the input matching circuit  207  can include the phase compensation circuit  203  therein to perform the above function.  
         [0044]     Next, it is possible to deliver the constant envelope signal to an input end of the transistor  209  without distortion, by matching the phase delay for a combination of the phase compensation circuit  203  and the input matching circuit  207  for the transistor  209  to a multiple (360°×n degree, where n is an integer) of 360° for a bandwidth of the delta-sigma modulated basic signal. Therefore, the present invention can implement a high-performance amplification system.  
         [0045]      FIGS. 3A  to  3 C are diagrams illustrating frequency and time domain characteristics of an input signal to a power amplifier based on a phase delay in a power amplification system according to the present invention.  FIGS. 3A  to  3 C show the simulation results for four available 2.14 GHz Wideband Code Division Multiple Access (WCDMA) channels, i.e. four Frequency Assignment (FA) signals, for the case where a baseband delta-sigma modulator is used.  
         [0046]     Referring to  FIG. 3A , there is shown a signal magnitude in the frequency and time domains when the phase delay is a multiple of 360° in the basic bandwidth. That is,  FIG. 3A  shows the simulation results on the signal magnitude in the frequency spectrum and the time domain for the signal input to the transistor  209  when the phase delay between the source device  201  and the transistor  209  is a multiple of 360° in the bandwidth of the delta-sigma modulated basic signal.  
         [0047]     From the time-domain graph of  FIG. 3A , it can be noted that the signal magnitude has a constant level. In  FIG. 3A , the frequency spectrum represents the delta-sigma modulated basic signal, the signal in the center represents the original input signal of WCDMA 4FA, and both outer band signals represent the quantization noise generated during delta-sigma modulation.  
         [0048]     The signal shown in  FIG. 3A  is equivalent to an output signal source of the delta-sigma modulated signal source, i.e. an output signal of the source device  201 . Therefore, it can be noted that the delta-sigma modulated signal is delivered to the transistor  209  without distortion.  
         [0049]     Referring to  FIG. 3B , there is shown a signal magnitude in the frequency and time domains when the phase delay is a multiple of 90° and 270° in the basic bandwidth. That is,  FIG. 3B  shows the simulation results on the signal magnitude in the frequency spectrum and the time domain for the signal input to the transistor  209  when the phase delay between the source device  201  and the transistor  209  is a multiple of 90° and 270° in the bandwidth of the delta-sigma modulated basic signal.  
         [0050]     Referring to  FIG. 3C , there is shown a signal magnitude in the frequency and time domains when the phase delay is a multiple of 180° in the basic bandwidth. That is,  FIG. 3C  shows the simulation results on the signal magnitude in the frequency spectrum and the time domain for the signal input to the transistor  209  when the phase delay between the source device  201  and the transistor  209  is a multiple of 180° in the bandwidth of the delta-sigma modulated basic signal.  
         [0051]     From  FIGS. 3B and 3C , it can be noted that the original signal of WCDMA 4FA remains unchanged in the frequency spectrum. It can also be noted that even though the original signal of WCDMA 4FA remains unchanged, a pattern of the quantization noises changes as shown in  FIG. 3A . As a result, the signal magnitude cannot remain constant in the time domain as shown in  FIGS. 3B and 3C . This is because an aliasing effect occurs between the basic signal and both harmonic signals of the basic signal, shown in  FIGS. 3B and 3C . In this phenomenon, signal distortion is maximized when the phase delay is 180° with respect to a bandwidth of the basic signal as shown in  FIG. 3C . The signal input to the amplifier is a square wave having only On-Off information, and the square wave has broadband characteristics. Therefore, the input signal suffers a different phase delay according to its frequency, and the delta-sigma modulated signal is distorted due to the phase delay. From  FIG. 3A  in which the phase delay is a multiple of 360°, it can be noted that the signal magnitude remains unchanged for the On time as shown in the time-domain characteristic graph. However, from  FIGS. 3B and 3C  in which the phase delay is 90° or 180°, it can be noted that the signal magnitude greatly changes for the On time as the signal is distorted. In conclusion, in order to deliver the delta-sigma modulated broadband signal to the transistor in the power amplifier without distortion, it is necessary to match the overall phase delay to a multiple of 360° for the bandwidth of the basic signal, using the broadband input matching circuit for the transistor and the phase compensation circuit such as the additional aliasing line.  
         [0052]     As can be understood from the foregoing description, the amplification system using the delta-sigma modulator includes the phase compensation circuit and the input matching circuit, making it possible to deliver the constant envelope signal delta-sigma modulated by the delta-sigma modulator to the power amplifier in the amplification system without distortion. By delivering the constant envelope signal to the power amplifier without distortion, it is possible to omit a linear amplification process of the power amplifier, contributing to an increase in efficiency of the power amplifier. The increase in the efficiency of the power amplifier contributes to achievement of the delta-sigma modulation system for high efficiency and improvement of the high-efficiency amplification system.  
         [0053]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.