JP2016178407A - Doherty amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Doherty amplifier which facilitates fault detection.SOLUTION: The Doherty amplifier comprises: carrier amplification means which amplifies a portion of a low envelope level in an input signal; peak amplification means which mainly amplifies a portion of a high envelope level in the input signal; directional coupling means which distributes the input signal, extracts a peak component of an envelope of the input signal on the basis of the distribution and supplies a constant bias voltage to the peak amplification means during a period of the extracted peak component; and detection means which monitors a voltage to be given to a device that forms the peak amplification means, or a current flowing to the device.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Doherty amplifier, and more particularly to increasing the efficiency of a Doherty amplifier.

  A Doherty amplifier used for a power amplifier is composed of two amplifiers, a carrier amplifier and a peak amplifier. When an input signal is input, in the Doherty amplifier, the carrier amplifier is operated with a class AB bias or a class A bias to amplify the low level of the envelope of the input signal and saturate the high level. The peak amplifier is operated with a class B bias or a class C bias to mainly amplify a high level portion.

  Due to soaring electricity costs and increasing environmental awareness, there is a demand for higher efficiency of high-frequency amplifiers used in wireless devices and the like. A Doherty amplifier is used as a high-efficiency method, but it is necessary to further increase the efficiency.

  Patent Document 1 relates to an amplifier that combines and outputs the outputs of a carrier amplifier circuit and a peak amplifier circuit, and it has been proposed to control the bias voltage of the peak amplifier circuit of the amplifier. In Patent Document 1, it is proposed to operate as a class C amplifier when the input is low by this bias voltage control, and to transition to class AB with a large idle current as the input increases.

JP 2007-116259 A

  It was difficult to detect a failure of the peak amplifier of the Doherty amplifier. Since the peak amplifier amplifies only the peak component, it does not always operate. For example, if an attempt is made to determine a failure based on whether or not the operation is performed only with the drain current, it cannot be determined whether there is no peak component and no drain current flows or whether there is a failure and no drain current flows. For this reason, it was difficult to detect a failure.

  An object of the present invention is to provide a Doherty amplifier that facilitates fault detection.

  In order to achieve the above object, a Doherty amplifier according to the present invention includes a carrier amplifying unit for amplifying a low level portion of an input signal envelope, and a peak amplifying unit for mainly amplifying a high level portion of the input signal envelope. Directional coupling means for distributing the input signal, extracting a peak component of the envelope of the input signal based on the input signal, and supplying a constant bias voltage to the peak amplification means during the extracted peak component period; And detecting means for monitoring a voltage applied to a device constituting the peak amplifying means and a current flowing through the device.

  According to the present invention, the failure detection can be easily performed by monitoring the voltage applied to the device constituting the peak amplification means by the detection means and the current flowing through the device.

FIG. 3 is a block diagram illustrating a Doherty amplifier according to an embodiment of the highest level concept of the present invention. It is a block diagram for demonstrating the Doherty amplifier by 1st Embodiment of this invention. It is a block diagram for demonstrating the Doherty amplifier by 2nd Embodiment of this invention. It is a figure showing each part operation waveform of the Doherty amplifier of FIG. It is a block diagram for demonstrating the Doherty amplifier used as the premise of this invention. It is a figure showing each part operation waveform of the Doherty amplifier of FIG. It is a figure showing the input / output characteristic of the peak amplifier in the Doherty amplifier of FIG. It is a figure showing the input-output characteristic of the peak amplifier in the Doherty amplifier of background art. It is a figure showing the input / output characteristic of the peak amplifier in the Doherty amplifier of FIG. It is a figure showing the input / output operation at the time of performing predistortion of the peak amplifier in the Doherty amplifier of background art.

  The present invention detects a peak component input timing of an input signal in a Doherty amplifier composed of two amplifiers, a carrier amplifier and a peak amplifier, and stops the amplification operation at the peak amplifier except when the peak component is amplified in the peak amplifier. To do. As a result, power consumption is reduced, and when the peak component is amplified, amplification with excellent linearity is performed by causing the peak amplifier to perform a class AB or class A bias operation. In addition, this feature enables reliable failure detection of the peak amplifier and protection of devices used in the amplifier.

  Before describing a preferred embodiment of the present invention, a Doherty amplifier which is a premise of the present invention will be described. FIG. 5 is a block diagram for explaining a Doherty amplifier as a premise of the present invention. FIG. 6 is a diagram showing operation waveforms of each part of the Doherty amplifier of FIG. FIG. 7 is a diagram showing the input / output characteristics of the peak amplifier in the Doherty amplifier of FIG. FIG. 8 is a diagram showing the input / output characteristics of the peak amplifier in the Doherty amplifier of the background art. FIG. 9 is a diagram showing the input / output characteristics of the peak amplifier in the Doherty amplifier of FIG. FIG. 10 is a diagram illustrating an input / output operation when performing predistortion of the peak amplifier in the Doherty amplifier of the background art.

  The Doherty amplifier shown in FIG. 5 includes a directional coupler 1, an input signal envelope detector 2, a peak component discriminator 3, a bias voltage controller 4, a delay adjuster 5, and quarter wavelength lines 6 and 9. 10, a peak amplifier 7, and a carrier amplifier 8.

  The carrier amplifier 8 amplifies the low level part of the envelope of the input signal. The peak amplifier 7 mainly amplifies the high level portion of the envelope of the input signal. In other words, the peak amplifier 7 amplifies an input signal having an amplitude (peak component) such that the output of the carrier amplifier 8 is saturated.

  The input signal envelope detector 2 detects the envelope amplitude of the input signal.

  The peak component discriminator 3 discriminates the period during which the peak component is input by comparing the level at which the amplitude is saturated from the envelope with the carrier amplifier 8 as the threshold value Vg−1. Pulse for the duration.

  The bias voltage controller 4 supplies a constant bias voltage Vg to the peak amplifier only during the peak component period.

  The delay adjuster 5 adjusts so that the timing of the peak component of the input signal input to the peak amplifier 7 and the bias voltage Vg supplied from the bias voltage controller 4 are the same.

  In the Doherty amplifier of FIG. 5, the directional coupler 1 distributes the input signal. The input signal envelope detector 2 detects the envelope amplitude of the input signal. The envelope (1) -a (see FIG. 6) of the input signal detected by the input signal envelope detector 2 is input to the peak component discriminator 3. The peak component discriminator 3 discriminates a period having a value higher than the threshold value as a peak component, and outputs a pulse (2) -a (see FIG. 6) only during the peak component period. The bias voltage controller 4 supplies a constant bias voltage (3) -a (see FIG. 6) to the peak amplifier 7 during the pulse period of the pulse output from the peak component discriminator 3.

  In the Doherty amplifier of FIG. 5, the input of the peak amplifier 7 is a waveform 31 that combines the envelope (1) -a of the input signal and the output waveform (3) -a of the bias voltage controller (see FIG. 6). The peak amplifier 7 amplifies the peak component at a level with good input / output characteristics, thereby amplifying only the peak component with a waveform having good linearity like the output signal waveform 32.

  When the input signal is input to the carrier amplifier and the peak amplifier, in the Doherty type amplifier, the carrier amplifier is operated with a class AB bias or a class A bias to amplify the low level of the envelope of the input signal, and the high level saturates the output. . The peak amplifier is operated with a class B bias or a class C bias to mainly amplify a high level portion.

  Accordingly, the peak amplifier operates with a class C bias or a class B bias as shown in FIG. The output signal waveform 42 is as shown in FIG. 8 with respect to the input signal waveform 41, and operates as a level signal that does not need to be amplified as a peak amplifier, and a gate bias voltage 44 of voltage Vg-2 to voltage Vg-3. The operating part consumes wasted power.

  Therefore, in order not to perform the output operation of the gate bias voltage 44, as shown in FIG. 9, the bias voltage is supplied only at the peak component, and the input of the peak amplifier is the combined waveform of the input signal and the output of the bias voltage controller 4. A waveform such as 51 is obtained. That is, the peak amplifier outputs an output signal waveform 52 when a combined waveform 51 of the input signal and the output of the bias voltage controller 4 is input. As a result, the operation indicated by the useless power consumption portion 44 in the peak amplifier of FIG. 8 can be stopped. This increases the efficiency of the peak amplifier.

  Although the peak amplifier can also be amplified at a level with good linearity by performing class AB bias operation, it cannot perform the amplification operation of only the peak component, and the power consumption increases due to the signal amplification operation of the useless power consumption portion 44 in FIG. . For this reason, power consumption cannot be suppressed unless it is a class B or class C bias operation, but the peak amplifier can also perform a class AB bias operation.

  In class B or class C bias operation, the gain is low, so that an output that requires a peak component may not be obtained. Therefore, by raising only the peak component of the input signal as shown by a portion 62 (shaded portion) raised by predistortion such as distortion compensation in FIG. 10, as shown by an output signal portion 64 necessary as a peak amplifier in FIG. There is a method of raising the output level to a required level with a peak amplifier.

  However, the input signal of the output signal portion 64 necessary as a peak amplifier is also input to the carrier amplifier, and a signal having an amplitude exceeding the saturation level is further input to the carrier amplifier, resulting in an excessive input and an increase in power consumption. The harmful effect of increasing distortion will occur.

  Therefore, in the Doherty amplifier of FIG. 5, when the peak amplifier is operated in class AB bias, the gain of peak component amplification becomes high, so that it is not necessary to increase the peak component input level excessively. The amount of transfer to the carrier amplifier is reduced, and the amount of distortion and power consumption due to saturation in the carrier amplifier can be reduced. Further, since the amplification linearity of the peak amplifier is improved, the waveform distortion at the peak amplifier output can be improved.

  Next, a Doherty amplifier according to a top-level conceptual embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram illustrating a Doherty amplifier according to a top-level conceptual embodiment of the present invention.

  The Doherty amplifier shown in FIG. 1 includes a peak amplifying unit 11, a carrier amplifying unit 12, a directional coupling unit 13, and a detecting unit 14.

  The carrier amplification means 12 amplifies the low level of the envelope of the input signal applied to the input terminal. The peak amplifying means 11 mainly amplifies the high level portion of the envelope of the input signal applied to the input terminal. The outputs of these amplifying means are combined and output from the output terminal.

  The directional coupling means 13 is inserted in the path between the input terminal and the peak amplifying means 11 and the carrier amplifying means 12 and distributes the input signal. The Doherty amplifier in FIG. 1 detects the envelope amplitude of the input signal based on the input signal distributed by the directional coupling means 13. Furthermore, the Doherty amplifier in FIG. 1 compares the detected envelope of the input signal with a set threshold value, and determines a period of a value higher than the threshold value as a peak component. Further, the Doherty amplifier of FIG. 1 generates a pulse only during the peak component period, and supplies a constant bias voltage to the peak amplifying means 11 only during the period of this pulse.

  Further, in the Doherty amplifier of FIG. 1, the detection means 14 monitors the voltage applied to the device constituting the peak amplification means 11 and controls it so as not to become below a preset specified value. Alternatively, in the Doherty amplifier of FIG. 1, it is determined whether or not a current is flowing through a device constituting the peak amplifying unit 11 at a timing when the detecting unit 14 performs an amplifying operation with a peak component.

  According to the Doherty amplifier of FIG. 1, the directional coupling means 13 distributes the input signal, extracts the peak component of the envelope of the input signal based on this, and applies a constant bias voltage to the peak amplifying means 11 only during the peak component period. Supply. Thereby, the power consumption of the Doherty amplifier can be reduced, and the Doherty amplifier can be highly efficient.

  Further, according to the Doherty amplifier of FIG. 1, since the detecting means 14 monitors the voltage applied to the device constituting the peak amplifying means 11 and controls the voltage so as not to become a preset specified value or less, the peak amplifying means 11 is controlled. The device to be configured can be protected. Alternatively, since the detection unit 14 determines whether or not a current is flowing through the device constituting the peak amplification unit 11 at the timing when the amplification operation is performed with the peak component, it is possible to determine the failure of the peak amplifier. Hereinafter, preferred embodiments of the present invention will be described in more detail.

[First Embodiment]
Next, the Doherty amplifier according to the first embodiment of the present invention will be described. FIG. 2 is a block diagram for explaining the Doherty amplifier according to the first embodiment of the present invention.

  As shown in FIG. 2, the Doherty amplifier of this embodiment includes a directional coupler 1, an input signal envelope detector 2, a peak component discriminator 3, a bias voltage controller 4, a delay adjuster 5, The quarter wavelength lines 6, 9, 10, the peak amplifier 7, and the carrier amplifier 8 are included. Furthermore, the Doherty amplifier of this embodiment includes a current detection circuit 91 and a discriminator 92 as an example of detection means.

  The current detection circuit 91 includes a resistance element inserted between the drain of a transistor as an example of a device constituting the peak amplifier 7 and the power supply potential Vd, and a comparator that detects a voltage across the resistance element. Including. The current detection circuit 91 monitors the drain current of the transistors constituting the peak amplifier 7.

  The discriminator 92 receives the output of the peak component discriminator 3 and the output of the current detection circuit 91 and outputs the output of the current detection circuit 91 during the peak component period of the envelope of the input signal discriminated by the peak component discriminator 3. To monitor. When the peak component is input to the peak amplifier 7 but the drain current is not flowing, the discriminator 92 determines that the peak amplifier 7 has failed.

  According to the Doherty amplifier of the present embodiment, the drain current of the transistors constituting the peak amplifier 7 is monitored during the peak component period of the envelope of the input signal determined by the peak component discriminator 3 as the Doherty amplifier increases in efficiency. be able to. Thereby, the failure of the peak amplifier 7 can be determined.

[Second Embodiment]
Next, a Doherty amplifier according to a second embodiment of the present invention will be described. FIG. 3 is a block diagram for explaining a Doherty amplifier according to a second embodiment of the present invention. FIG. 4 is a diagram showing operation waveforms of each part of the Doherty amplifier of FIG.

  As shown in FIG. 3, the Doherty amplifier of this embodiment includes a directional coupler 1, an input signal envelope detector 2, a peak component discriminator 3, a bias voltage controller 4, a delay adjuster 5, The quarter wavelength lines 6, 9, 10, the peak amplifier 7, and the carrier amplifier 8 are included. Furthermore, the Doherty amplifier of this embodiment includes a clipping circuit 71 as an example of a detection unit. The clipping circuit 71 monitors a gate-source voltage Vgs of a transistor as an example of a device constituting the peak amplifier 7 and clips it so that the gate-source voltage Vgs does not become a specified value or less.

  The clipping circuit 71 in FIG. 3 includes a diode inserted between the bias voltage signal line output from the bias voltage controller 4 and the power supply potential Vp.

  The minimum value (Vgs-min) of the gate-source voltage Vgs is specified for devices constituting the peak amplifier 7, for example, transistors, but the specified minimum value Vgs-min for class B bias and class C bias depending on the input signal. May be:

  In particular, when using a device whose gate voltage is weak to a negative potential, such as LD-MOS (Laterally Diffused Metal Oxide Semiconductor) devices, as shown in FIG. A clipping circuit 71 is provided. The clipping circuit 71 functions so that the combined signal waveform 81 of the input signal and the pulse gate bias voltage shown in FIG.

  Rather than using the clipping circuit 71, the combined signal waveform 81 of the input signal and the pulse gate bias voltage in FIG. 4 should not be less than the specified minimum value Vgs-min as indicated by the specified value 84 by other means. You can also. That is, as a method for preventing the gate-source voltage Vgs from being lower than the specified minimum value Vgs-min, the lower voltage Vg-L supplied by the bias voltage controller 4 at a timing that is not the peak component is used as the device Vgs-min. A higher voltage Vg-L. In addition, when the high voltage Vg-L is output, the output impedance of the bias voltage controller 4 is set to a low impedance when viewed from the gate side of the peak amplifier 7. As a result, the input signal can be absorbed by the voltage Vg-L so that it does not become a voltage lower than the voltage Vg-L.

  According to the Doherty amplifier of the present embodiment, the clipping circuit 71 monitors the gate-source voltage Vgs of the transistors constituting the peak amplifier 7 and clips the gate-source voltage Vgs so that it does not become a specified value or less. This improves the efficiency of the Doherty amplifier and protects the device constituting the peak amplifier 7 even when the peak amplifier 7 is configured using a device whose gate voltage is weak to a negative potential, such as an LD-MOS device. be able to.

[Other Embodiments]
In the above-described Doherty amplifiers of the first and second embodiments, the basic Doherty amplifier has one carrier amplifier and one peak amplifier. However, the present invention is not limited to this. In addition, when the number of peak amplifiers of the Doherty amplifier is N, the peak component discriminator can determine the peak as N stages. In this case, for example, N threshold values different from each other are prepared in the peak component discriminator, and the N-stage peak component is discriminated by comparing the envelope of the input signal with the N threshold values in order or simultaneously. Good.

  The effect by embodiment of this invention is described anew. First, by not performing the amplification operation except when the peak component is amplified by the peak amplifier, it is possible to amplify even unnecessary signals and reduce the power consumed wastefully.

  Second, when the peak component is amplified by the peak amplifier, the amplification factor is low in the class B or class C bias, so that the peak component of the input signal needs to be higher. Then, since a signal having a higher peak component is input to the carrier amplifier, the carrier amplifier becomes excessively input, and distortion due to output saturation increases. According to the embodiment of the present invention, this can be avoided.

  Third, since the peak amplifier is not always operating, it was difficult to determine the failure only by monitoring the drain current, but it can be determined that the current is not flowing when it should move, so that the failure can be detected accurately. become.

  Fourth, although the minimum value Vgs-min of the gate-source voltage is specified by the device, the class B bias and the class C bias may be less than the specified minimum value Vgs-min depending on the input signal. According to the embodiment of the present invention, it is possible to eliminate a failure by having a protection function that does not lower the voltage between the gate and the source below the minimum value.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to this. For example, the Doherty amplifier of the first embodiment shown in FIG. 2 may be combined with the clipping circuit 71 of the Doherty amplifier shown in FIG. 3 to protect the transistors constituting the peak amplifier. It goes without saying that various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Directional coupler 2 Input signal envelope detector 3 Peak component discriminator 4 Bias voltage controller 5 Delay regulator 6, 9, 10 1/4 wavelength line 7 Peak amplifier 8 Carrier amplifier 11 Peak amplifying means 12 Carrier amplifying means 13 Directional coupling means 14 Detection means 71 Clipping circuit 91 Current detection circuit 92 Discriminator

Claims (6)

  Carrier amplification means for amplifying a low level portion of the envelope of the input signal, peak amplification means for mainly amplifying a high level portion of the envelope of the input signal, and distributing the input signal, and based on this, the input signal A directional coupling means for extracting a peak component of the envelope of the envelope and supplying a constant bias voltage to the peak amplifying means during a period of the extracted peak component; a voltage applied to a device constituting the peak amplifying means; and the device A Doherty amplifier having detection means for monitoring a current flowing through   The detection means includes a current detection circuit that detects a current flowing through a device constituting the peak amplification means, and a discriminator that determines whether or not the current is flowing at a timing when the peak amplification means performs an amplification operation with a peak component. The Doherty amplifier according to claim 1.   3. The Doherty amplifier according to claim 2, wherein the discriminator discriminates a detection output of the current detection circuit based on a period of a peak component of an envelope of the input signal distributed and extracted by the directional coupling unit. .   The said detection means monitors the voltage given to the device which comprises the said peak amplification means, and includes the clipping circuit which controls so that it may not become below the preset specified value. The Doherty amplifier described in 1.   5. The Doherty amplifier according to claim 4, wherein the clipping circuit includes a diode inserted between a signal line of the bias voltage supplied to the peak amplifying unit and a certain power supply potential. The peak amplification means includes N (N is an integer of 2 or more) peak amplifiers,
The Doherty amplifier according to any one of claims 1 to 5, wherein a peak component of an envelope of the input signal distributed and extracted by the directional coupling unit is determined in N stages.

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