JP2002050934A - Feed forward amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feed forward amplifier which allows an excessive spurious generation to be suppressed, until control of distortion extraction is converged, without making the output of an error amplifier high power. SOLUTION: An amplitude limiter which limits the amplitude of the distortion component inputted to a loop for eliminating the distortion is provided in the front stage of the error amplifier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power amplifier suitable for use in a wireless communication system or a wired communication system.
In particular, the present invention relates to a feedforward amplifier having two types of loops, distortion extraction and distortion removal.

[0002]

2. Description of the Related Art A feedforward amplifier includes a distortion extraction loop for extracting only a distortion component from an output signal of an amplifier by canceling a main signal component, and amplifying the extracted distortion component and then canceling the output signal of the amplifier by canceling the distortion component. It is composed of two types of signal cancellation loops of a distortion removal loop that uses only the main signal component.

[0003] Such a conventional amplifier (for example, Japanese Unexamined Patent Publication No.
FIG. 7 shows an example of the general configuration of
Shown in The signal input from the input terminal 1 to the distortion extraction loop 25 is split into two by the power divider 2, one of which is input to the main amplifier 5 via the variable attenuator 3 and the phase shifter 4, and the other is input to the delay device 7. Is done. The signal to the main amplifier 5 is amplified to a required power. However, since the main amplifier 5 generates distortion due to its non-linearity, the output signal of the main amplifier 5 includes a distortion component in addition to the main signal component. FIG. 8A shows the state of the output signal of the main amplifier 5. In the figure, the horizontal axis represents frequency, the vertical axis represents relative power, M represents a main signal component, and D represents a distortion component. The output signal is M + D.

On the other hand, since the delay device 7 has no element causing distortion, only the main signal component M is output (see FIG. 8B). In the adder 8, the output signal M + D of the main amplifier 5 and the main signal component M output from the delay unit 7 are added in opposite phases, so that the main signal component M is canceled and the distortion component D
Is extracted (see FIG. 8C).

The distortion component is divided into two by the power divider 12, one of which is supplied to the level detector 18, and the other is a distortion component sent to the distortion removal loop 26. The control unit 16 controls the variable attenuator 3 so that the output of the level detector 18 is minimized, that is, the main signal component is canceled by the adder 8.
And the phase shifter 4. There is an example in which the variable attenuator 3 and the phase shifter 4 are arranged on the delay unit 7 side, but the effect is the same.

The distortion component input to the distortion removal loop 26 is
Error amplifier 15 via variable attenuator 13 and phase shifter 14
And is amplified. The adder 10 adds the output signal M + D of the main amplifier 5 that has passed through the delay unit 9 and the output signal (distortion component D) of the error amplifier 15 in opposite phases to each other to obtain a distortion component D
Offset. As a result, the main signal component M from which the distortion component D has been removed is output from the adder 10 as shown in FIG. 8D.

[0007] The output signal of the adder 10 is
, One is sent to the distortion detector 19, and the other is sent to the output terminal 20. The control unit 17 controls the variable attenuator 13 and the phase shifter 14 so that the output of the distortion detector 19 is minimized, that is, the adder 10 achieves the cancellation of the distortion component.

By simultaneously performing the two systems of cancellation control, the feedforward amplifier becomes a feedforward type linear compensation power amplifier having optimum operating conditions.

[0009]

In the above-mentioned conventional example,
Until the convergence of the distortion extraction control from the start of the distortion extraction loop 25 to the convergence, the cancellation is insufficient, so that not only the distortion component but also the main signal component is included in the output of the distortion extraction loop 25. During this time, a large signal is input to the error amplifier 15, thereby distorting the error amplifier 15, and a new distortion signal is output from the output terminal 20.

[0010] The new distortion signal is emitted as spurious signals outside the transmitter, for example, to the antenna. However, since the generation of the new distortion signal is particularly undesirable, an error amplifier having a high maximum output power must be used to suppress the generation. And the power consumption increases. Until the distortion extraction is completed, an excessive signal is input to the error amplifier, which may cause a problem that the error amplifier may be damaged. Further, spurious components emitted outside the transmitter become disturbance waves to the outside.

An object of the present invention is to provide a feedforward amplifier which suppresses generation of excessive spurious until control of distortion extraction converges without increasing output power of the error amplifier. It is in.

[0012]

According to a first aspect of the present invention, there is provided a feed-forward amplifier including an amplitude limiter for limiting the amplitude of a distortion component input to a distortion removal loop, at a stage preceding the error amplifier. Features. Since the input amplitude of the error amplifier is limited, it is possible to suppress the spurious emitted before the control of the distortion extraction converges, and it is possible to avoid increasing the output power of the error amplifier, thereby increasing the power consumption. Can be prevented. In addition, the limitation of the input amplitude can prevent the error amplifier from being damaged. The above-described amplitude limiter can be realized by, for example, a limiter amplifier.

The above object can also be achieved by using a variable attenuator arranged before the error amplifier as a variable attenuator whose attenuation changes according to the level detection result in the distortion extraction loop.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a feedforward amplifier according to the present invention will be described in more detail with reference to embodiments of the present invention shown in the drawings. It should be noted that the same symbols in FIGS. 1, 4, and 5 indicate the same or similar objects.

FIG. 1 shows an embodiment of the invention in which a limiter amplifier is used as an amplitude limiter provided in a stage preceding the error amplifier. In FIG. 1, a distortion extraction loop 25 includes a power divider 2 that bisects a signal input to an input terminal 1, and one signal output by the power divider 2 via a variable attenuator 3 and a phase shifter 4. A main amplifier 5 for inputting and amplifying, a power divider 6 for dividing an output signal of the main amplifier 5 into two, and one output signal output from the power divider 6 and the other output from the power divider 2 via a delay unit 7 And an adder 8 for inputting the above signal.

The control system for distortion detection includes a power divider 12 for dividing the output signal (addition result) of the adder 8 into two parts, a level detector 18 for detecting the level of one output signal output from the power divider 12, and the like. And a control unit 1 for receiving the level detection result of the level detector 18 and controlling the variable attenuator 3 and the phase shifter 4
And 6.

In the above two configurations, the adder 8 removes the main signal component from the output signal of the main amplifier 5 by canceling,
Output the distortion component as the addition result. At this time, the control unit 16
Controls the variable attenuator 3 and the phase shifter 4 so that the level detection result of the level detector 18 is minimized, that is, the cancellation of the main signal component is achieved. And the power distributor 2
Is the distortion component input to the distortion removal loop 26.

Further, in FIG. 1, the distortion removal loop 26
A limiter amplifier 21 for inputting a distortion component, an error amplifier 15 for inputting and amplifying an output signal of the limiter amplifier 21 via a variable attenuator 13 and a phase shifter 14, and an error amplifier 1
5 and an adder 10 to which the other output signal output from the power divider 6 via the delay unit 9 is input.

The control system for removing distortion includes a power divider 11 for dividing the output signal (addition result) of the adder 10 into two, and a distortion detector for detecting a distortion component in one of the output signals output from the power divider 11. And a control unit 17 that receives the distortion detection result of the distortion detector 19 and controls the variable attenuator 13 and the phase shifter 14.

In the above two configurations, the adder 10 removes the distortion component from the output signal of the main amplifier 5 by canceling, and outputs a main signal component from which the distortion component has been removed as an addition result.
At this time, the control unit 17 controls the variable attenuator 13 and the phase shifter 14 so that the detection result of the distortion detector 19 is minimized, that is, the cancellation of the distortion component is achieved. Then, the other main signal component output from power divider 2 is output to output terminal 20.

Since the main signal component is not sufficiently canceled until the distortion extraction control converges after the operation of the distortion extraction loop 25 starts, the addition result of the adder 8 cancels out the distortion component. The remaining main signal component is added, and the amplitude of the addition result increases. The limiter amplifier 21 operates to limit the increased amplitude.

Here, an example of the configuration of the limiter amplifier 21 is shown in FIG. Diodes D1 and D2 having opposite polarities are respectively connected to a power supply V1 and a resistor R1 connected to the resistor R1 connected to the amplifier 30.
Connected via V2. The power sources V1 and V2 have opposite polarities, but have the same voltage value. When the amplitude of the output signal of the amplifier 30 exceeds this voltage value, the diode D
Either one of D1 and D2 becomes conductive and the amplitude of the output signal is limited so as not to exceed the voltage values of the power supplies V1 and V2.

FIG. 3 shows transmission characteristics of a signal from the input terminal 31 to the output terminal 32 of the limiter amplifier 21. The horizontal axis in FIG. 3 is the input amplitude Pin, and the vertical axis is the output amplitude Pout.
And the output amplitude is limited to the amplitude Pmax based on the above voltage value.

The amplitude limiter used in the present invention is not limited to the above-mentioned limiter amplifier. For example, a circuit using a diode as a feedback circuit of the amplifier or the amplifier 3 shown in FIG.
A circuit having an amplitude limiting function such as a circuit in which 0 is omitted can be adopted.

According to the embodiment of the present invention, the error amplifier 1
5, the spurious emitted from the output terminal 20 can be suppressed before the control of the distortion extraction converges, and the error amplifier 15 is prevented from being damaged and its power consumption is reduced. can do.

FIG. 4 shows an embodiment of the invention in which the amount of attenuation of the variable attenuator 13 is increased without using the limiter amplifier 12 until the control of distortion extraction converges. In FIG. 4, a variable attenuator 13 is a variable attenuator that receives control from the control unit 17 and also receives control from the control unit 16.

Here, the controller 1 controls the variable attenuator 13 in accordance with the level detected by the level detector 18.
The operation of No. 6 will be described. In the initial state, the attenuation of the variable attenuator 13 is set to be large. After the power of the feedforward amplifier is turned on, after the level detected by the level detector 18 becomes equal to or lower than a specified level, that is, after the control of the distortion extraction in the distortion extraction loop 25 is almost completed, the control unit 16 changes the variable state. The attenuation of the attenuator 13 is reduced, and the variable attenuator 13 is controlled by the control unit 17 only when the distortion extraction control is completed.

The variable attenuator 13 and the level detector 18
Each part of the embodiment of the present invention other than the control unit 16 and FIG.
Since they are the same as those shown in FIG. Also in the embodiment of the present invention, the input amplitude of the error amplifier 15 is effectively limited until the distortion extraction control converges.

In the above, the spurious emission in a short time until the control of the distortion extraction converges and the inconvenience of the error amplifier 15 has been a problem. In this case, the spurious emission is constantly continued, which causes a serious situation. Further, when the operation becomes defective due to the failure of the control unit 17, the distortion is not removed, and the distortion component becomes large spurious and is disadvantageously discharged to the outside.

FIG. 5 shows an embodiment of the invention in which such spurious emission is prevented from continuing. In FIG. 5, reference numeral 22 denotes a preliminary control unit having the same configuration as the control unit 16;
Is a preliminary control unit having the same configuration as the control unit 17. Control unit 1
The switches 50 and 51 controlled by the level detector 18 are connected to the input and output sides of the control unit 6 and the spare control unit 22, respectively. By operation of these switches, one of the control units is selected and the level detection is performed. Connected to the vessel 18. A switch 5 controlled by a distortion detector 19 is provided on each input / output side of the control unit 17 and the preliminary control unit 23.
2 and 53 are connected, and the operation of these switches selects one of the control units and causes the distortion detector 19 to operate.
Connected to.

Other configurations of the embodiment of the present invention are the same as those in the case where the limiter amplifier 21 is omitted in the configuration shown in FIG. 1, and a description thereof will be omitted. The operation of the embodiment of the present invention will be described. When the level detector 18 detects the signal extracted by the distortion extraction loop 25, even if a long time has elapsed compared to the time when the distortion extraction control converges,
If the level does not fall below the specified value, the level detector 18 determines that the control unit 16 has failed, and the control unit 1
The switches 50 and 51 connected to the
Switch to connection to. Similarly, when the distortion detector 19 detects the distortion component of the signal output from the distortion removal loop 26, if the level of the distortion component does not fall below the specified level, the distortion detector 19
Determines that the control unit 17 has failed, and switches the switches 52 and 53 connected to the control unit 17 to the connection to the spare control unit 23.

The preliminary control unit 2 according to the embodiment of the present invention
2 and 23 can be installed in the feedforward amplifier having the configuration of FIG. 1 having the limiter amplifier 21. In the case of the configuration of FIG. 4 as well, a spare controller corresponding to the controllers 16 and 17 is provided. It is possible to obtain the same effect in each case.

Next, FIG. 6 shows an example of an embodiment of the invention of a transmitting apparatus using the above-mentioned feed-forward amplifier as a power amplifier for supplying high-frequency power to an antenna.
The transmitting device includes a modulator 64 that modulates input data from an input terminal 61, a mixer 65 that performs frequency conversion on a modulated wave output from the modulator 64, a local oscillator 66 that supplies a carrier to the mixer 65, and a mixer 65. The bandpass filter 67 limits the frequency band of the output modulated wave, and the feedforward amplifier 28 amplifies the modulated wave of the bandpass filter 67 and supplies the antenna 29 with high-frequency power.

Hereinafter, the signal generation process of the transmitting apparatus will be described. The serial input data from the input terminal 1 is subjected to serial / parallel conversion by the modulator 64, then converted to multi-valued data, and further subjected to quadrature modulation to receive, for example, 16QAM (Qua
drature Amplitude Modulation). The modulated wave output from the modulator 64 is frequency-converted by the mixer 25 into a radio frequency band by a carrier from the local oscillator 26. Unnecessary harmonics are removed from the frequency-converted modulated wave by passing through the band-pass filter 27.
The modulated wave output from the bandpass filter 27 is amplified to a predetermined transmission power by a feedforward amplifier 28,
Transmitted by the antenna 29.

Here, the feedforward amplifier 28
Is an amplifier described above, so that excessive input to the error amplifier 15 until the control of distortion removal converges is avoided, thereby suppressing spurious emission from the antenna 29. Further, since the damage of the error amplifier 15 is prevented, a highly reliable transmission device can be realized.

[0036]

According to the present invention, since the input amplitude of the error amplifier is limited, the spurious emitted during the time until the control of the distortion extraction converges is suppressed, and the error amplifier is prevented from being damaged. In addition, it is possible to realize a feedforward amplifier capable of reducing its power consumption. Also, by employing such a feedforward amplifier, a highly reliable transmission device can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram for explaining an embodiment of a feedforward amplifier according to the present invention;

FIG. 2 is a circuit diagram for explaining an example of a limiter amplifier used for the feedforward amplifier shown in FIG.

FIG. 3 is a diagram showing input / output characteristics of a limiter amplifier.

FIG. 4 is a circuit diagram for explaining another embodiment of the feedforward amplifier of the present invention.

FIG. 5 is a circuit configuration diagram for explaining still another embodiment of the feedforward amplifier of the present invention.

FIG. 6 is a circuit configuration diagram for explaining a transmission device using the feedforward amplifier of the present invention.

FIG. 7 is a circuit configuration diagram for explaining an example of a conventional feedforward amplifier.

FIG. 8 is a diagram for explaining the operation of a distortion extraction loop and a distortion removal loop.

[Explanation of symbols]

1: input terminal, 2, 6, 11, 12 ... power distributor, 3,
13: variable attenuator, 4, 14: phase shifter, 5: main amplifier,
7, 9: delay device, 8, 10 adder, 15 error amplifier, 16, 17 control unit, 18 level detector, 19 ...
Distortion detector, 20 ... output terminal, 21 ... limiter amplifier.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Fumito Tomaru 32nd Miyukicho, Kodaira-shi, Tokyo Hitachi Electronics Co., Ltd. (72) Takuya Takahashi 32nd Miyukicho, Kodaira-shi, Tokyo Hitachi Electronics Co., Ltd. Within the Development Laboratory (72) Inventor Hiroshi Kishida 1-280, Higashi-Koigakubo, Kokubunji-shi, Tokyo F-term within the Central Research Laboratory, Hitachi, Ltd. HA19 HA25 HA38 HN03 HN11 HN15 KA00 KA15 KA16 KA20 KA23 KA26 KA32 KA44 KA53 MA14 SA14 TA01 TA02 TA03 5J091 AA01 AA41 AA51 CA21 CA27 CA36 CA56 FA01 FA18 HA19 HA25 HA38 KA00 KA15 KA16 KA16 KA16 KA16 KA16 AA51 CA21 CA27 CA36 CA56 FA01 FA18 HA19 HA25 HA38 KA00 KA15 KA16 KA20 KA23 KA26 KA32 KA44 KA53 MA 14 SA14 TA01 TA02 TA03

Claims (5)

[Claims] 1. A distortion extraction loop including a main amplifier for amplifying an input signal, a first adder for extracting a distortion component of an output signal of the main amplifier by canceling the main signal component, and a distortion component output from the distortion extraction loop. An error amplifier to amplify and a distortion removal loop including a second adder for extracting a main signal component of the output signal of the main amplifier by canceling a distortion component using an output signal of the error amplifier; A feed-forward amplifier, wherein the removal loop includes an amplitude limiter for limiting an input amplitude before the error amplifier. 2. The feedforward amplifier according to claim 1, wherein the amplitude limiter is a limiter amplifier. 3. A distortion extraction loop including a main amplifier for amplifying an input signal, a first adder for extracting a distortion component of an output signal of the main amplifier by canceling the main signal component, and a distortion component output from the distortion extraction loop. A distortion removal loop including an error amplifier that amplifies via a variable attenuator, and a second adder that extracts a main signal component of the output signal of the main amplifier by canceling a distortion component using an output signal of the error amplifier; In addition to controlling the level and phase of the input signal to the main amplifier according to the detection result of the level detector, the distortion extraction control of the distortion extraction loop converges. And a controller for increasing the attenuation of the variable attenuator. 4. A distortion extraction loop including a main amplifier for amplifying an input signal, a first adder for extracting a distortion component of an output signal of the main amplifier by canceling the main signal component, and a distortion component output from the distortion extraction loop. A distortion removal loop including an error amplifier to be amplified, a second adder for extracting a main signal component of the output signal of the main amplifier by canceling a distortion component using an output signal of the error amplifier, and an output of the first adder A level detector for detecting a signal level, a first control unit for controlling a level and a phase of an input signal to an error amplifier according to a detection result of the level detector, and an output signal of a second adder. A distortion detector that detects a distortion component included therein, a second control unit that controls the level and phase of an input signal to an error amplifier according to a detection result of the distortion detector, and when the first control unit fails. Switch to the first used A feed-forward amplifier, comprising: a spare control unit of (1), and a second spare control unit that is switched and used when the second control unit fails. 5. A transmission device comprising the feedforward amplifier according to claim 1.