Patent Application
20110254622
The present invention relates to power amplifying devices mainly used for a radio communication transmitter, in particular, to those that can vary a power supply voltage supplied to an amplifier on the basis of an amplitude modulation component of an input signal.
Radio communication systems such as mobile telephone systems and wireless LANs (Local Area Networks) that have appeared in recent years use modulation formats such as QPSK (Quadrature Phase Shift Keying) and multi-value QAM (Quadrature Amplitude Modulation). In these modulation formats, when a signal changes between symbols, since its waveform is involved in amplitude modulation, the amplitude (envelop) of a radio frequency modulation signal superimposed on a carrier signal of a microwave bandwidth varies time by time. The ratio of the peak power and the average power of the radio frequency modulation signal is referred to as PAPR (Peak-to-Average Power Ratio). When a signal having a large PAPR is amplified with a high linearity that is maintained, a power supply device needs to supply sufficiently large power to an amplifier so as to prevent the waveform of the amplified signal from being distorted with peak power and secure high linearity of the amplified signal. In other words, the amplifier needs to be operated in a large back-off power region that is sufficiently lower than the saturated output power restricted by the power supply voltage.
Generally, since radio frequency amplifiers that amplify a radio frequency signal according to the class A system or class AB system have maximum efficiency nearly at the saturated output power level, if they are operated in the large back-off power region, their average efficiency lowers.
Although the OFDM (Orthogonal Frequency Division Multiplexing) system has been used in the next-generation mobile phone systems, wireless LANs, digital television broadcasts, and so forth, since their PAPR tends to increase, the average efficiency of radio frequency amplifiers further lowers. Thus, it is desired that radio frequency amplifiers operate with high efficiency even in the large back-off power region.
As a system that amplifies a signal in the large back-off region and with wide dynamic range and high efficiency, a power amplifying device referred to as the EER (Envelope Elimination and Restoration) system has been proposed in Non-patent Document 1.
The EER system proposed in Non-patent Document 1 divides an input modulation signal into a phase modulation component and an amplitude modulation component. Thereafter, the phase modulation component with a constant amplitude is inputted to the amplifier in such a manner that phase modulation information is maintained. At this point, the amplifier is always operated at the nearly saturated output power level having the maximum efficiency.
On the other hand, the amplitude modulation component is amplified with high efficiency by a class D amplifier or the like in such a manner that amplitude modulation information is maintained and then supplied as a power supply voltage (modulation power supply) whose output intensity has been modulated.
When the power amplifying device is operated in such a manner, the amplifier is also operated as a multiplier and combines the phase modulation component and amplitude modulation component of the modulation signal and outputs the combined result. Thus, the amplifier can obtain an output modulation signal amplified with high efficiency not in the large back-off power region. As a system similar to the EER system, the so-called ET (Envelop Tracking) system is also known. This system has been reported for example in Non-patent Document 2 and so forth.
The ET system is the same as the EER system in the structure that uses a class D amplifier or the like that amplifies the amplitude modulation component of the input modulation signal in such a manner that the amplification modulation information is maintained and supplies the resultant signal as a power supply voltage (modulation power supply) whose output intensity has been modulated to the amplifier.
The EER system is different from the ET system in structure in which the former inputs only a phase modulation signal with a constant amplitude to the amplifier so as to operate it at a nearly saturation output power level; while the latter inputs an input modulation signal containing both amplitude modulation component and phase modulation component to the amplifier so as to linearly operate it.
Although the ET system is inferior to the EER system in efficiency because the amplifier of the former linearly operates, since only a bare minimum power based on the amplitude modulation component of the input modulation signal is supplied to the amplifier, the former can have higher efficiency than the structure that supplies a constant power voltage to the amplifier.
In addition, the ET system can be more easily realized than the EER system because the former allows a timing margin, at which the amplitude modulation component and the phase modulation component are combined, to be loose.
The EER system and the ET system ordinarily use a modulation power supply that converts the amplitude modulation component into a pulse modulation signal and performs switching amplification for the pulse modulation signal using a class D amplifier or the like. As a pulse modulation system for the EER and the ET system, the PWM (Pulse Width Modulation) system has been traditionally used; however, Patent Document 1 and Patent Document 2 propose structures that use the delta modulation system (or PDM (Pulse Density Modulation)) that has higher linearity than the foregoing systems. Moreover, in recent years, the sigma delta modulation system and so forth that have a high SNR (Signal to Noise Ratio) have been used as pulse modulation systems.
Relevant standards for radio communication systems such as mobile telephone systems and wireless LANs using digital modulation systems that have appeared in recent years require that ACPR (Adjacent Channel Leakage Power Ratio) and EVM (Error Vector Magnitude) should be suppressed to a predetermined constant value or below.
To satisfy these standards for power amplifying devices according to the EER system and ET system, it is said that the bandwidth in which a pulse modulator and a class D amplifier with which a modulation power supply is provided needs to be at least twice that of a modulation signal. For example, the modulation bandwidth of WCDMA (Wideband Code Division Multiple Access) used in mobile phone systems is around 5 MHz, whereas the modulation bandwidth of IEEE 802.11 a/g used in wireless LANs is around 20 MHz. Generally, it is difficult to switch a large power at high speed and realize a modulation power supply that operates in such a wide bandwidth.
In such a situation, a structure of a modulation power supply that operates with high efficiency and in a wide bandwidth has been proposed in Non-Patent Document 3. The structure of the power amplifying device proposed in Non-Patent Document 3 (hereinafter referred to as the first related art reference) is shown in
The power amplifying device according to the first related art reference interlocks linear amplifying section 3 that operates in a wide bandwidth, but with low efficiency and switching regulator section 2 that operates in a narrow bandwidth, but with high efficiency so as to supply modulation power (power supply voltage) 11 with high efficiency in a wide bandwidth to amplifier 1.
A specific operation of the power amplifying device is as follows.
Amplitude signal 9 that is an amplitude modulation component of an input modulation signal is inputted to linear amplifying section 3 composed of voltage follower 31 or the like.
An output current of linear amplifying section 3 is converted into a voltage signal by current detection resistor 42 and inputted to hysteresis comparator 41 In this example, if polarities are selected such that when the current flows from linear amplifying section 3, the output voltage of comparator 41 becomes High and when the current flows to linear amplifying section 3, the output voltage of hysteresis comparator 41 becomes Low, a pulse width modulation signal based on the intensity of the input signal is outputted from hysteresis comparator 41.
Gate driver 5 turns on or off switching device 21 composed of, for example, an MOS FET (Metal Oxide Semiconductor Field Effect Transistor) based on the output signal of hysteresis comparator 41. Switching device 21 is comprised of switching regulator section 2 in combination with diode 22; switching regulator section 2 which amplifies the amplitude of the pulse width modulation signal to Vcc1.
The pulse width modulation signal that has been amplified is integrated by inductor 6 and thereby the switching frequency component is removed therefrom.
An error component contained in an output current of inductor 6 is compensated by voltage follower 3 and supplied as a power supply voltage to amplifier 1. At this point, since a current that flows in linear amplifier 31 with low efficiency contains only the error component, the power consumed in linear amplifier 31 is small and most of the signal components of amplitude signal 9 are amplified by switching regulator with high efficiency. Thus, the efficiency of the entire power supply modulator can be improved.
The structure of the power amplifying device proposed in Patent Document 3 (hereinafter referred to as the second related art reference) is shown in
In the power amplifying device according to the second related art reference as well as that according to the first related art reference, an output current of linear amplifying section 102 is detected by resistor 108, the result is amplified by differential amplifier 110, and then inputted to feedback circuit 106.
Feedback circuit 106 compares an output signal of differential amplifier 110 and reference signal Vref and supplies the compared result typically to pulse modulator 136 that performs pulse width modulation (PWM). Output signal 134 of pulse modulator 136 is inputted to switching amplifying section 104 including at least one switching device 126 and a filter composed of inductor 124 and capacitor 128 so as to control switching device 126.
Output current Isw of switching amplifying section 104 is connected to the output of linear amplifying section 102 through current detection resistor 108. Output voltage Vout of switching amplifying section 104 is compensated by linear amplifying section 102 so as to decrease ripple (switching noise) contained in output current Isw.
Since only a switching noise current ideally flows in linear amplifying section 102, it does not consume large power. Thus, a modulation power supply with high accuracy and high efficiency can be accomplished.
To ideally operate the modulation power supply that supplies power (power supply voltage) to radio frequency amplifier 1 that has been described above, output impedance Zo needs to be sufficiently smaller than the input impedance of the power supply of radio frequency amplifier 1.
Since the power amplifying device according to the first related art reference shown in
If the gain of linear amplifier 31 is sufficiently high, the output impedance of linear amplifying section 31 gets close to 0.
However, in the structure shown in
Since current detection resistor 42 not only causes a deterioration in the efficiency of radio frequency amplifier 1, due to voltage drop, but also causes output voltage Vout of the modulation power supply to slightly deviate from amplitude signal 9 due to voltage drop, noise tends to be superimposed on output voltage Vout, resulting in causing ACPR (Adjacent Channel Leakage Power Ratio) of output signal 12 of radio frequency amplifier 1 not to satisfy the communication standards as a problem of the power amplifying device according to the second related art reference.
In the power amplifying device according to the second related art reference shown in
[Patent Document 1] Japanese Patent Laid-Open No. 3207153, (Page 8,
[Patent Document 2] U.S. Pat. No. 5973556, (Page 3,
[Patent Document 3] U.S. Pat. No. 5905407, (Page 2,
[Non-patent Document 1] Lenard R. Kahn, “Single-sideband Transmission by Envelope Elimination and Restoration”, PROCEEDINGS OF THE I. R. E., Vol. 40, pp. 803-806, 1952.
[Non-patent Document 2] J. Staudinger, B. Gilsdorf, D. Newman, G. Norris, G. Sandwniczak, R. Sherman and T. Quach, “HIGH EFFICIENCY CDMA RF POWER AMPLIFIER USING DYNAMIC ENVELOPE TRACKING TECHNIQUE”, 2000 IEEE MTT-S Digest, vol. 2, pp. 873-876.
[Non-patent Document 3] F. Wang, A. Ojo, D. Kimball, P Asbeck and L. Larson, “Envelope Tracking Power Amplifier with Pre-Distortion Linearization for WLAN 802.11g”, 2004 IEEE MTT-S Digest, vol. 3, pp. 1543-1546.
An object of the present invention is to provide power amplifying devices that can vary a power supply voltage supplied to an amplifier according to an amplification of a modulation signal, in particular, to those that have high efficiency and high linearity.
To accomplish the foregoing object, an exemplary aspect of the power amplifying device of the present invention is a power amplifying device that amplifies a modulation signal containing an amplitude modulation component and a phase modulation component, comprising:
a radio frequency amplifier that amplifies said modulation signal and outputs the resultant signal;
a linear amplifying section that adds an output voltage to a power supply voltage supplied to said radio frequency amplifier and negatively feeds back the power supply voltage supplied to said radio frequency amplifier such that the power supply voltage matches the amplitude modulation component of said modulation signal with a predetermined ratio;
a control signal generation section that detects a direction in which an output current of said linear amplifying section flows and generates a pulse modulation signal according to the direction of the current;
a switching amplifying section that controls connection and disconnection of a DC current based on said pulse modulation signal as a control signal so as to perform switching amplification for an output signal of said linear amplifying section and to supply the resultant signal as said power supply voltage to said radio frequency amplifier; and
a DC power supply that supplies said DC current to said switching amplifying section.
Alternatively, another exemplary aspect of the power amplifying device of the present invention is a power amplifying device that amplifies a modulation signal containing an amplitude modulation component and a phase modulation component, comprising:
a radio frequency amplifier that amplifies the phase modulation component of said modulation signal and outputs the resultant signal;
a linear amplifying section that adds an output voltage to a power supply voltage supplied to said radio frequency amplifier and negatively feeds back the power supply voltage supplied to said radio frequency amplifier such that the power supply voltage matches the amplitude modulation component of said modulation signal with a predetermined ratio;
a control signal generation section that detects a direction in which an output current of said linear amplifying section flows and generates a pulse modulation signal according to the direction of the current;
a switching amplifying section that controls connection and disconnection of a DC current based on said pulse modulation signal as a control signal so as to perform switching amplification for an output signal of said linear amplifying section and to supply the resultant signal as said power supply voltage to said radio frequency amplifier; and
a DC power supply that supplies said DC current to said switching amplifying section.
[FIG. 1]
[FIG. 2]
[FIG. 3]
[FIG. 4]
[FIG. 5]
[FIG. 6]
Next, with reference to drawings, the present invention will be described.
As shown in
Linear amplifying section 3 adds the output voltage to a power supply voltage supplied to radio frequency amplifier 1 and negatively feeds back the power supply voltage supplied to radio frequency amplifier 1 such that the power supply voltage matches an amplitude modulation component of modulation signal 8 at a predetermined ratio.
Control signal generation section 4 generates a pulse modulation signal that becomes High or Low depending on the direction of the output current of linear amplifying section 3 and outputs the pulse modulation signal to switching amplifying section 2.
Switching amplifying section 2 performs switching amplification for amplitude signal 9 based on the pulse modulation signal as a control signal that is outputted from control signal generation section 4, adds a predetermined DC voltage to the amplified signal, and outputs the resultant signal. The output voltage of switching amplifying section 2 is added to the output voltage of control signal generation section 4 and thereby modulation voltage 11 is generated as a power supply voltage supplied to radio frequency amplifier 1.
In the power amplifying device according to this exemplary embodiment, modulation voltage 11 that is the power supply voltage supplied to radio frequency amplifier 1 is negatively fed back to linear amplifying section 3.
Radio frequency amplifier 1 linearly amplifies modulation signal 8 according to the class A system or class AB system based on modulation voltage 11 as a power supply and outputs radio frequency modulation signal 12 which has been modulated with respect to amplitude and phase.
As shown in
On the other hand, linear amplifying section 3 is provided with linear amplifier 31. Control signal generation section 4 is provided with hysteresis comparator 41, current detection resistor 42, and gate driver 5.
In the power amplifying device according to this exemplary embodiment, linear amplifying section 3 is composed of a linear amplifier (for example, a voltage follower) including a negative feedback loop. Thus, the waveform of the output voltage accords to the waveform of amplitude signal 9 with high accuracy. The output of linear amplifying section 3 is inputted to control signal generation section 4.
Control signal generation section 4 is provided with current detection resistor 42 that detects a current that is outputted from linear amplifying section 3 and a comparator (hysteresis comparator 41) and generates a control signal for example that becomes High when the current flows from linear amplifying section 3 and becomes Low when the current flows thereto. The generated control signal is inputted to switching amplifying section 2.
Switching amplifying section 2 controls connection/disconnection of switching device 21 based on the control signal generated by control signal generation section 4 so as to perform switching amplification for the output signal of linear amplifying section 3.
A current that is outputted from switching amplifying section 2 is smoothened by inductor 6 and added to the output signal of linear amplifying section 3 so as to compensate the voltage.
Modulation voltage 11 that has been compensated is supplied as a power supply voltage to radio frequency amplifier 1 that linearly amplifies modulation signal 8, resulting in always supplying only a bare minimum power (power supply voltage) to radio frequency amplifier 1. Thus, the power amplifying device according to this exemplary embodiment can operate radio frequency amplifier 1 with higher efficiency than the case in which a constant voltage is supplied as a power supply voltage.
Since the output impedance of the modulation power supply is not affected by current detection resistor 42, the power amplifying device according to this exemplary embodiment operates as a more ideal modulation power supply than do the power amplifying devices according to the related art references. Next, this effect will be described by comparing a specific structure (
In the power amplifying device according to the first related art reference shown in
where r0 is the output resistance of linear amplifier 31, Ao is the gain of linear amplifier 31, β is the feedback ratio, β=1 in the structure shown in
Generally, since output resistance ro of linear amplifier (operational amplifier) is sufficiently small and gain Ao is sufficiently large, the first term of the right side of the foregoing formula (1) becomes so small that it can be ignored, namely Zo Rsense.
On the other hand, output impedance Z0 of the modulation power supply viewed from the power supply terminal of radio frequency amplifier 1 shown in
In this case, due to the same reason as the foregoing formula (1), the right side of the formula (2) becomes so small that it can be ignored. In other words, the right side becomes Zo≈0 that denotes that radio frequency amplifier I can operate as an ideal modulation power supply.
Thus, since the power amplifying device according to this exemplary embodiment has higher following accuracy for amplitude signal 9 than does the power amplifying devices according to the related art references, the former can realize a modulation power supply having a low switching nose. As a result, radio frequency modulation signal 12 with high linearity can be obtained.
Next, with reference to
As shown in
Linear amplifying section 3 is composed of linear (differential) amplifier 31, typically an operational amplifier, and operates such that the input signal (amplitude signal 9) matches feedback 13 (
An output current (
Gate driver 5 turns on or off switching device 21 composed of, for example, an MOS FET based on the output signal of hysteresis comparator 41.
Power supply voltage Vcc1 is supplied to one terminal of switching device 21 and a cathode of diode 22 of anode ground type and inductor 6 are connected to the other terminal of switching device 21.
When the control signal that is outputted from hysteresis comparator 41 is High, switching device 21 is connected and thereby a current flows from power supply voltage Vcc1 to inductor 6. At this point, if the ON resistance of switching device 21 is so small such that it can be ignored, the potential of a connection node of switching device 21 and diode 22 rises to Vcc1. Thus, since a reverse voltage is applied to diode 22, no current flows.
In contrast, when the control signal that is outputted from hysteresis comparator 41 becomes low, switching device 21 is disconnected and a current that is flowing from voltage source Vcc1 to inductor 6 is blocked.
Since inductor 6 maintains a current that is flowing, a counter electromotive force occurs, resulting in causing the potential of the connection node between switching device 21 and diode 22 to drop. When the potential of the connection node between switching device 21 and diode 22 becomes a negative potential and becomes equal to or lower than a forward voltage of diode 22, a current flows from the ground potential to inductor 6 through diode 22.
In this series of operations, while a current is flowing, since a voltage is not applied between both terminals of switching device 21 and diode 22, switching amplification is performed for the output signal of linear amplifier 31 ideally with an efficiency of 100%.
The switching amplified current is integrated by inductor 6 and thereby a switching frequency component is removed therefrom (
In addition, a switching noise component contained in the output voltage of switching amplifying section 2 is compensated (smoothened) by linear amplifier 31 (
Radio frequency amplifier 1 linearly amplifies modulation signal 8 that has been inputted based on the power supply voltage that is the output voltage of switching amplifying section 2. At this point, since only a minimum power (power supply voltage) is supplied to radio frequency amplifier 1 based on the amplitude of amplitude signal 9, radio frequency amplifier 1 can always operate nearly with saturation power having high efficiency.
In the power amplifying device according to this exemplary embodiment, as shown in
Moreover, in the power amplifying device according to this exemplary embodiment, since the output voltage of switching amplifying section 2 is negatively fed back to linear amplifier 31, the influence of the potential drop by current detection resistor 42 can be removed from the power supply voltage supplied to radio frequency amplifier 1.
As shown in
If such slight switching noise enters radio frequency modulation signal 12 that is output ed from radio frequency amplifier 1, normal communication may be affected.
On the other hand, as shown in
Thus, since the switching noise does not enter radio frequency modulation signal 12 that is outputted from radio frequency amplifier 1, normal communication can be performed.
When these effects are rephrased, in the first related art reference shown in
Although the power amplifying device shown in
In addition, the structure of switching amplifying section 2 is not limited to the structure shown in
Although the power amplifying device shown in
Now, with reference to the exemplary embodiments, the present invention has been described. However, it should be understood by those skilled in the art that the structure and details of the present invention may be changed in various manners without departing from the scope of the present invention.
The present application claims a priority based on Japanese Patent Application No. 2008-330710 filed on Dec. 25, 2008, the entire contents of which are incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-330710 | Dec 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/070950 | 12/16/2009 | WO | 00 | 6/6/2011 |
