JP2011041002A - High frequency amplifier and efficiency increasing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency amplifier which amplifies a signal having a difference of high between a peak and an average at a broad band, and to provide an efficiency increasing method. <P>SOLUTION: A discrimination amplifier 5 inputs a digital signal to monitor the signal level. When the signal level is equal to or less than a given input level of the digital signal, the discrimination amplifier supplies a switching power amplifier 2 with a power supply of a voltage v2, and outputs a pulse signal which has a different pulse duty and a fixed output amplitude, and is modulated by ΣΔ to the switching power amplifier 2, and when the signal level exceeds the given input level, the discrimination amplifier supplies a power supply of a voltage V1 higher than v2, outputs the pulse signal having the same pulse duty and amplitude as at the given input level to a ΣΔ modulator 1, and adds a signal of an amplitude corresponding to the exceeding level to an output signal of the switching power amplifier 2 to perform amplitude modulation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a high-efficiency and high-linearity high-frequency amplifier and a high-efficiency method.

  CDMA and OFDM modulation schemes used for communication, broadcasting, etc. that transmit a large amount of information have a large ratio between the peak power and the average power of the modulation signal, and the output amplifier takes a back-off from saturation power to ensure linearity. There is a need. However, if the back-off is performed, the efficiency of the amplifier generally decreases in class A and class AB operations. Therefore, there is a demand for an amplification method that prevents a decrease in the efficiency of the amplifier even at the operating point where the back-off is performed.

  As one of the methods, there is a method in which a sigma delta (hereinafter referred to as ΣΔ) modulation is applied to an input signal and a subsequent PA (power amplifier) is operated by 1 bit (for example, Non-Patent Document 1). If this method is used, a conventionally used unit such as a transmission frequency converter is not required, and the circuit configuration of the transmitter is simplified.

  There is a bandpass ΣΔ method in the digital ΣΔ modulation method, and the PA must be switched at a sampling frequency four times the RF (radio radio wave) frequency. For RF signals of several hundreds of MHz to several GHz, such as cellular phones If this is applied, there is a problem that the switching loss of the PA increases and the efficiency of the PA decreases.

FIG. 5 is a functional block diagram for explaining the operation of a conventional high frequency amplifier using the ΣΔ method.
In FIG. 5, a conventional high-frequency amplifier using the ΣΔ method includes a digital processing unit 8 that outputs a baseband digital signal of a signal to be transmitted wirelessly, and the output baseband signal is ΣΔ modulated, that is, a 1-bit pulse train. ΣΔ modulator 1 that converts the modulated signal into a modulated signal and outputs it, a power amplifier power amplifier (hereinafter referred to as SWPA) 2 that switches and amplifies the modulated signal and outputs it as a signal radio wave, and a switching amplified signal radio wave that are unnecessary. BPF3 which suppresses noise and adjusts the output of a required band for transmission from an antenna (not shown).

  When the SWPA2 is a voltage-controlled power amplifier (PA), the maximum output is obtained when the duty ratio of the output voltage is 50%. A high-frequency switching amplifier is used for SWPA2, but a loss of Cout × Vd × 1/2 occurs each time switching is performed. Here, Cout is the output capacity of SWPA2, and Vd is the drain voltage of SWPA2.

  As shown in Table III on page 2517 of Non-Patent Document 1, when a ΣΔ modulated sine wave is input to a class D amplifier in voltage control switch mode, the efficiency of the amplifier is 34%. In the case of a WCDMA signal having a peak to average power ratio (PAR) of 7.1 dB, the efficiency is 7.1%, and when the PAR is 10 dB, the efficiency is reduced to 3.4%.

  As described above, the conventional high-frequency amplifier using the ΣΔ modulation method has a problem that the efficiency is poor for a signal with a high PAR.

Thomas Johnson, Shawn P. Stapleton, RF Class-D Amplification With Bandpass Sigma-Delta Modulator Drive Signals.IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS-I: REGULAR PAPERS, VOL.53, NO.12, DECEMBER 2006 p.2507-2520

  Conventional high-frequency amplifiers using the ΣΔ modulation method have a problem of low efficiency when a signal having a high peak-to-average level ratio (PAR) is amplified.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a high-frequency amplifier that amplifies a wideband and high PAR signal with high efficiency, and a high-efficiency method.

  In order to achieve the above object, a high-frequency amplifier according to the present invention is a high-frequency amplifier that modulates a wirelessly transmitted digital signal by ΣΔ modulation, amplifies power with a switching power amplifier, and outputs the signal through a bandpass filter. A ΣΔ modulator that is input and converted to a ΣΔ-modulated pulse signal and outputs the pulse signal to the switching power amplifier, a first power source that outputs a voltage v1, and a second power source that outputs a voltage v2 lower than v1 When the signal level of the digital signal input to the ΣΔ modulator is monitored and the signal level is equal to or lower than a predetermined level, the pulse width changes corresponding to the signal level input to the ΣΔ modulator. The ΣΔ modulated pulse signal is output to the switching power amplifier, and the second power source is connected to the switching power amplifier. The control for supplying the power of the voltage v2 to output a transmission signal having a constant amplitude, and when the predetermined level is exceeded, the ΣΔ modulator has the same pulse width as that when the predetermined level is input. The band-pass filter is configured to output a pulse signal, supply the power supply voltage v1 to the switching power amplifier, and perform an amplitude modulation to add an amplitude corresponding to the excess level to the constant amplitude. And a monitoring control means for performing a control to output the output.

  In addition, the high-frequency amplifier high-efficiency method of the present invention includes a switching power amplifier, a ΣΔ modulator, a first power source that outputs a voltage v1, a second power source that outputs a voltage v2, and a monitoring control unit. In the method for improving the efficiency of a high-frequency amplifier that ΣΔ modulates a digital signal to be transmitted wirelessly, amplifies the power with a switching power amplifier, and outputs the amplified signal through a band-pass filter, the power is output to the switching power amplifier. The voltage v1 output from the first power supply is set to be higher than the voltage v2 output from the second power supply, and the monitoring control means sets the signal level of the digital signal input to the ΣΔ modulator. And when it is below a predetermined level, a ΣΔ modulated pulse whose pulse width changes in accordance with the signal level input to the ΣΔ modulator. A signal having a predetermined amplitude is supplied to the switching power amplifier from the second power source to output a transmission signal having a predetermined amplitude, and the predetermined level is set. Is exceeded, the pulse signal having the same pulse width as that when the predetermined level is input is output to the ΣΔ modulator, and the power supply voltage of v1 is supplied to the switching power amplifier. Control is performed to output to the band-pass filter as a transmission signal subjected to amplitude modulation that adds amplitude corresponding to the excess level to the amplitude.

  According to the present invention, it is possible to provide a high-frequency amplifier and a high-efficiency method for amplifying a signal having a high peak and average difference in a wide band with high efficiency.

The functional block diagram explaining operation | movement of the high frequency amplifier concerning the Example of this invention. Operation | movement explanatory drawing of the switching amplifier (CVSCD) of a nonpatent literature reference 1. FIG. SWPA input signal and output waveform diagram. The functional block diagram explaining the operation | movement of the modification of the high frequency amplifier concerning the Example of this invention. The functional block diagram explaining operation | movement of the high frequency amplifier using the conventional (SIGMA) delta system.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram for explaining the operation of the high-frequency amplifier according to the embodiment of the present invention.
1, the description of the high-frequency amplifier according to the embodiment of the present invention is omitted with respect to the same matters as in FIG. 5, but the D / A converter is further added to the configuration of the conventional high-frequency amplifier using the ΣΔ method shown in FIG. 4, a discrimination amplifier 5, a switch transistor Tr1, a choke coil 6, and a backflow prevention diode 7 are added.

  The baseband signal output from the digital processing unit 8 for wireless transmission is converted into an analog signal by the D / A converter 4 and, for example, an envelope detected level monitor signal is input to the discrimination amplifier 5. In the discrimination amplifier 5, a threshold Vth set higher than an average level having a high signal existence probability is set in advance with respect to the level monitor signal, and when this threshold Vth is exceeded, the transistor Tr1 is turned on to obtain the input voltage. Outputs a proportional voltage.

  For example, the threshold value Vth is a value corresponding to a level approximately 6 dB higher than the average output level when the PAR is 8 dB, and is set so that the probability is about several percent. In the SWPA 2, the power source V 2 having a voltage v 2 is normally supplied to the drain via the choke coil 6 and the diode 7. On the other hand, a power source V1 having a voltage v1 higher than that of the power source V2 is supplied to the collector of the transistor Tr1. If the level of the input signal to the high frequency amplifier is equal to or lower than the threshold value Vth, the power source V2 is supplied to the SWPA2, and if it exceeds the threshold value Vth, the power source V1 is supplied. The voltage v1 of the power source V1 is preferably set to a voltage that can be output even for a peak input that is about 10 dB larger than the average input level.

Now, consider the operation of the switching power amplifier that amplifies the signal from the ΣΔ modulator.
FIG. 2 is an operation explanatory diagram of a switching amplifier (CVSCD: Complementary-Voltage Switched Class-D amplifier) of a non-patent cited document.
Fig. 2 (a) is a schematic diagram of a CVSCD amplifier (Fig. 6) and Fig. 2 (b) (Fig. 7 (a)) shows a signal with a constant amplitude and 50% duty cycle with zero current. FIG. 2 (c) (non-patent citation FIG. 7 (b)) shows a state diagram in the case where the ΣΔ modulation signal is inputted and the current is not zero current switching.

  Although the WCDMA signal is a signal having a large level difference between the average output level and the peak level, the probability of outputting the peak level signal is not large, and the signal amplitude is the average output level in most time.

  Therefore, in the embodiment of the present invention, when the level of the input signal of the amplifier (SWPA2) is equal to or less than the specified value (threshold value), a fixed voltage (v2) is applied to the drain terminal of the switching amplifier as a power supply, and the output of the ΣΔ modulator A transmission signal having a constant amplitude is output by a switching operation in which the signal is input as it is.

  On the other hand, when a signal with an increased PAR is input, in other words, with a signal having a large peak level above the threshold, the pulse width (duty) that changes the output signal from the ΣΔ modulator to the amplifier in accordance with the level of the input signal is set. Switch to an operation that maintains a constant pulse width. The power supply voltage supplied to the drain terminal of the amplifier is controlled to output a transmission signal modulated in the amplitude direction to improve efficiency.

  That is, the amplitude modulation is performed by controlling the power supply voltage so that the voltage is not the duty ratio of the pulse but the voltage is v1 at the maximum with respect to SWPA2 which is the CVSCD amplifier in FIG. If the threshold Vth is set to perform normal ΣΔ modulation up to a point higher than the average level by a predetermined level as described above, the SWPA2 has a voltage (v2) lower than the voltage (v1) required at the peak below the threshold Vth. ).

  That is, a signal with a large PAR, such as WCDMA, has a low probability of being a peak output, and therefore operates at a low drain voltage v2 for most of the time, so that a reduction in efficiency can be prevented.

  As described above, if the input signal to the high-frequency amplifier is equal to or lower than the threshold Vth of the input level to the discrimination amplifier 5 corresponding thereto, the transistor Tr1 remains off and the power source V2 is supplied to SWPA2, exceeding the threshold Vth. The transistor Tr1 is turned on and the power source V1 is supplied.

  At the same time, the control signal (threshold information) controls the ΣΔ modulator 1 to perform a normal operation of changing the pulse width in proportion to the input signal amplitude up to the voltage for turning on the transistor Tr1 output from the discrimination amplifier 5. ) Or a voltage is input to the ΣΔ modulator 1 from the digital processing unit 8 or the discrimination amplifier 5.

  Further, while the control signal is applied, the output from the ΣΔ modulator 1 is maintained so that the input signal has the same pulse width and amplitude as when the input corresponding to the threshold Vth is applied. In other words, the ΣΔ modulator 1 is set so that the pulse width of the modulation signal to be output is fixed when the level of the input signal exceeds the threshold value Vth.

  When the level of the input signal exceeds the threshold value Vth, the voltage of the maximum v1 whose amplitude changes via the transistor Tr1 turned on by the discrimination amplifier 5 is supplied to the power source of the SWPA2, and as a result, A transmission signal having an amplitude increased corresponding to the amplitude of the output of the normal ΣΔ modulator when the input signal is less than or equal to the threshold value Vth corresponding to the amount of the input signal exceeding the threshold value Vth is output to the BPF 3.

FIG. 3 is a waveform diagram of the input signal and output of SWPA2.
FIG. 3 shows a state where amplitude modulation is performed in which the output amplitude increases when the input signal exceeds Vth.

  Since the transistor Tr1 is operated linearly, for example, close to class A, the efficiency including the power supply is not good at first glance. However, in the case of a signal having a large ratio between the peak power and the average power of the modulation signal such as CDMA and OFDM, the input signal is a threshold value. Since the threshold value Vth is set so that the existence probability of Vth or higher is lowered, the efficiency of the high frequency amplifier as a whole is improved.

FIG. 4 is a functional block diagram for explaining the operation of the modified example of the high-frequency amplifier according to the embodiment of the present invention.
In FIG. 4, the high frequency amplifier further includes two transistors Tr2 and Tr3 having a common emitter connected to the configuration of FIG. 1, a bias unit 9, and a capacitor C as a decoupling capacitor.

  Also, two types of bias power sources are supplied to the drain of the high-frequency amplifier SWPA2: a bias of the voltage v1 supplied at the time of high output and a bias of the voltage v2 for the low output. The output of the discrimination amplifier 5 is input to the bias unit 9, and when the level of the input signal is equal to or lower than the specified value (Vth), Tr3 is turned off and Tr2 is turned on by the bias unit 9.

  The bias unit 9 is a variable voltage power source whose output voltage is controlled by the discrimination amplifier 5. This variable voltage power source controls the base voltages of Tr3 and Tr2. That is, if the input signal level is equal to or lower than the threshold value Vth, Tr3 is turned off and Tr2 is turned on. If the input signal level is higher than the threshold value Vth, the base voltage is controlled so that Tr3 is turned on and Tr2 is turned off. As a circuit configuration, an active element circuit that outputs the above-described voltage according to an input from the discrimination amplifier 5 that compares the magnitudes of input signals, a DSP circuit, or the like may be used.

  When Tr3 is turned off and Tr2 is turned on, the power source V2 of voltage v2 is applied to SWPA2 via the choke coil 6 and the diode 7. At this time, since the capacitor C is connected to the collector side of Tr2, the impedance of the baseband signal as viewed from the power supply system side from the output terminal of SWPA2 is low.

  SWPA2 is a high-efficiency switching amplifier and operates in class D. At this time, if the impedance of the power supply system in the baseband signal is high, the power supply voltage also changes due to the fluctuation of the power supply current of SWPA2, and drain modulation is applied.

  As a result, the distortion characteristics of the high-frequency amplifier deteriorate, and in particular, an amplifier circuit using a DPD (digital predistortion circuit) in the digital processing unit 8 causes a distortion deterioration characteristic called a memory effect. In order to further correct this, there is a problem that the DPD becomes large-scale. Since the SWPA2 of the high frequency width device of this embodiment has a low impedance of the power supply system, it is possible to suppress deterioration due to the memory effect.

  When the level of the input signal is equal to or higher than the specified value Vth, the bias unit 9 turns on Tr3 and turns off Tr2. Since Tr3 operates as an emitter follower, the collector or drain (power supply) voltage of the amplifier operates following the input signal output from the discrimination amplifier 5.

  Since the voltage v1 of the power source V1 supplied to the collector of Tr3 is set so that v1> v2, unlike the conventional simple amplifier, the collector voltage of SWPA2 does not change discontinuously and the input level is detected. Since it changes corresponding to the voltage, the distortion characteristics of SWPA2 can be improved and amplitude modulation can be applied.

  The above Tr3 and Tr2 may be bipolar transistors or FETs. Alternatively, a combination of a bipolar transistor on one side and an FET on the other side may be used.

  In the case of a bipolar transistor, the collector voltage is controlled, and in the case of an FET, the drain voltage is controlled. Here, these controlled voltages are collectively referred to as a bias voltage. In the case of bipolar transistors and FETs, the collector may be read as the drain, the emitter as the source, and the base as the gate.

  In the present invention, the configuration, combination, processing procedure, and the like can be changed without departing from the spirit of the invention. For example, the D / A converter 4, the discrimination amplifier 5, and the bias unit 9 have independent configurations, but the signal level comparison of the discrimination amplifier 5 is performed digitally, and the bias unit 9 performs digital conversion of the digital signal. A bias signal generating unit that generates a bias voltage for controlling each transistor from the obtained value may be used.

1 ΣΔ modulator 2 SWPA (switching power amplifier)
3 BPF
4 D / A converter 5 Discriminating amplifier 6 Choke coil 7 Reverse voltage prevention diode 8 Digital processing unit 9 Bias unit Tr1, Tr2, Tr3 Switch transistor

Claims (7)

In a high-frequency amplifier that ΣΔ modulates a digital signal transmitted wirelessly, amplifies power with a switching power amplifier, and outputs through a bandpass filter.
A ΣΔ modulator that receives the digital signal and outputs it to the switching power amplifier as a ΣΔ-modulated pulse signal;
A first power supply that outputs a voltage v1;
A second power source that outputs a voltage of v2 lower than v1;
Monitor the signal level of the digital signal input to the ΣΔ modulator,
When the signal level is equal to or lower than a predetermined level, the switching power amplifier outputs a ΣΔ modulated pulse signal whose pulse width changes corresponding to the signal level input to the ΣΔ modulator, and the switching power Control for supplying a power of the voltage v2 from the second power source to the amplifier and outputting a transmission signal having a constant amplitude;
When the predetermined level is exceeded, the pulse signal having the same pulse width as that when the predetermined level is input is output to the ΣΔ modulator, and the power supply voltage v1 is supplied to the switching power amplifier. A high-frequency amplifier comprising: a monitoring control unit that performs control to output the band-pass filter as an amplitude-modulated transmission signal that adds an amplitude corresponding to the excess level to the constant amplitude . The monitoring control means includes
2. The high-frequency amplifier according to claim 1, wherein the predetermined level is set to a value that is equal to or higher than an average input level assumed for the input signal level and lower than a maximum peak level. The second power supply is connected to a power supply terminal of the switching power amplifier via a backflow prevention diode,
The first power supply is connected to a collector of a transistor, an emitter thereof is connected to a power supply terminal of the switching power amplifier, a base thereof is connected to the monitoring control means,
The monitoring control means includes
When the input signal level is less than or equal to the predetermined level, the transistor is turned off and the second power supply is supplied to the switching power amplifier,
When the input signal level is equal to or higher than the predetermined level, the transistor is turned on to supply the first power source to the switching power amplifier, and the output amplitude corresponding to the voltage exceeding the predetermined level is the constant level. 3. The high frequency amplifier according to claim 1, wherein a control signal added to the amplitude is output to a base of the transistor. 4. The high-frequency amplifier according to claim 1, wherein the voltage v <b> 1 is a voltage capable of the amplitude modulation that can correspond to a peak signal that is approximately 10 dB larger than the average input level. 5. The high-frequency amplifier is
The second power supply is connected to a power supply terminal of the switching power amplifier via a backflow prevention diode;
A base is connected to the output terminal of the monitoring control means, a collector is grounded via a capacitor, a base is connected to the output terminal of the monitoring control means, and a collector is connected to the first power supply A third transistor having an emitter connected to the emitter of the second transistor and connected to a power supply terminal of the switching power amplifier;
When the input signal level is equal to or lower than the predetermined signal level, the supervisory control unit sets the third transistor to OFF and the second transistor to ON to switch the second power source to the switching power. When the signal is supplied to an amplifier and the predetermined input level is exceeded, the second transistor is turned off and the third transistor is turned on, and the amplitude of the output corresponding to the level exceeding the predetermined signal level is 3. The high frequency amplifier according to claim 1, wherein a control signal added to the constant output amplitude is output to a base of each transistor. A switching power amplifier, a ΣΔ modulator, a first power source that outputs a voltage v1, a second power source that outputs a voltage v2, and a monitoring control means;
In a method for improving the efficiency of a high-frequency amplifier that ΣΔ modulates a digital signal transmitted wirelessly, amplifies power with a switching power amplifier, and further outputs through a bandpass filter
The voltage v1 output from the first power supply that outputs power to the switching power amplifier is set higher than the voltage v2 output from the second power supply,
The monitoring control means monitors the signal level of the digital signal input to the ΣΔ modulator,
If it is below a certain level,
The ΣΔ modulated pulse signal whose pulse width changes corresponding to the signal level input to the ΣΔ modulator is output to the switching power amplifier, and the switching power amplifier receives the v2 from the second power supply. To control the output of a constant amplitude transmission signal
When the predetermined level is exceeded, the pulse signal having the same pulse width as that when the predetermined level is input is output to the ΣΔ modulator, and the power supply voltage v1 is supplied to the switching power amplifier. A method for increasing the efficiency of a high-frequency amplifier, characterized in that control is performed to output the band-pass filter as a transmission signal subjected to amplitude modulation that adds an amplitude corresponding to the excess level to the constant amplitude. The monitoring control means includes
7. The method for improving the efficiency of a high-frequency amplifier according to claim 6, wherein the predetermined level is set to a value not less than an average input level of the input signal level to be assumed and less than a maximum peak level.

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