JPH10200340A - Feedforward amplifier - Google Patents

Abstract

(57) [Problem] There is no conventional feed-forward amplifier that is small and can obtain a distortion suppression amount of 40 dB or more. When operating as a feedforward amplifier, amplitude and phase deviations must be within 0.5 dB to ensure that the amount of distortion suppression is at least 30 dBc within the operating band.
Since it is necessary to be within a degree, a plurality of filters 11 are inserted in parallel behind the main amplifier 4 so that the characteristics of the frequency, phase, and amplitude of the main amplifier 4 become opposite phases. , And flatten the phase and amplitude characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed-forward amplifier which is applied to a transmission / reception apparatus installed in a base station for performing digital mobile communication and extracts and removes distortion generated in the amplifier.

[0002]

2. Description of the Related Art In mobile communication, a feed-forward amplifier is generally known for simultaneously amplifying multi-channel radio waves.

FIG. 2 shows a configuration diagram of a conventional feedforward amplifier.

An input signal 21 is divided by a directional coupler 22 into a main amplifier 24 and a delay line 26 of a detection loop.

On the main amplifier 24 side, the input signal 21 is first inserted with the pilot signal 20, passes through a vector adjuster 23 comprising a variable phase shifter and a variable attenuator, and is amplified by the main amplifier 24. At this time, distortion occurs. Then, the signal is transmitted to the signal combining unit 27 of the directional coupler 25.

An input signal of the delay line 26 on the detection loop side is transmitted to the signal synthesizing unit 27 through the delay line 26.

The synthesizing unit 27 includes a delay line 26 and a main amplifier 24.
The vector adjuster 23 is adjusted so that the phase with the side is shifted by 180 degrees and the amplitude of the signal is the same, so that the signal level is minimized. Here, the variable phase shifter and the variable attenuator of the vector adjuster 23 are adjusted so that the input pilot signal 20 is minimized.

Therefore, the output from the signal synthesizer 27 is dominated by the amount of distortion in the main amplifier 24, and is amplified by the auxiliary amplifier 29 through the vector adjuster 28 in the distortion detection loop.

On the other hand, the signal from the main amplifier 24 passes through the directional coupler 25, passes through the delay line 30 of the distortion removal loop, and is transmitted to the signal combining section 32 of the directional coupler 31.

The phase and attenuation of the vector adjuster 28 are adjusted so that the signal synthesizer 32 cancels the distortion.
It is configured to extract the least distorted signal.

FIG. 2 also shows the configuration of a control system in which the phase and attenuation of each vector adjuster can be automatically adjusted to minimize the distortion.

[0012]

By the way, as shown in the above conventional example, the delay line 26 and the delay line 30 are incorporated in the distortion detection loop and the distortion removal loop, respectively.

The length of this line is enormous in order to make it the same as the time of the signal line on the vector adjuster 23 and main amplifier 24 side of the distortion detection loop. For example, 20
The delay time is about 40 ns. Since this is a signal after the main amplifier 24 as in the case of the distortion removal loop, a delay line of a high-power cable is required.

Winding the cable many times increases the loss, reduces the efficiency, and reduces the overall size of the feedforward amplifier, which is a very difficult factor.

Further, each of the vector adjusters adjusts the phase and the amplitude, but the main amplifier and the auxiliary amplifier cannot adjust the deviation of the phase and the amplitude with respect to the own frequency. For this reason, there is a case where the amount of distortion improvement of the entire feedforward amplifier cannot be reduced, and there is a problem that the signal is transmitted as spurious.

An object of the present invention is to provide a small-sized feedforward amplifier capable of obtaining a distortion suppression amount of 40 dB or more in consideration of such a problem of the conventional feedforward amplifier.

[0017]

SUMMARY OF THE INVENTION The present invention comprises a first phase shifter, a first vector adjuster having a first attenuator, a distortion detection loop having a main amplifier, a second phase shifter and a second phase shifter. A second vector adjuster having two attenuators and a distortion removal loop having an auxiliary amplifier; a pilot signal generator;
A pilot detector for detecting the pilot signal, wherein the distortion removal loop is connected after the distortion detection loop, and the distortion generated in the main amplifier is extracted by the distortion detection loop and amplified by the auxiliary amplifier. Then, the output of the main amplifier is re-injected in the opposite phase of the amplitude, the distortion component of the main amplifier is canceled, and the distortion is compensated for. And a plurality of the filters are set in parallel with respect to the signal line.

Further, according to the present invention, a plurality of filters are provided in the above-described distortion detection loop, and the frequency characteristics of the filters in the distortion detection loop are converted into the phase and amplitude of the frequencies of the vector adjuster and the main amplifier. A feedforward amplifier characterized by flattening the phase and amplitude characteristics of the entire distortion detection loop by making the characteristics opposite to the characteristics.

Further, according to the present invention, a plurality of filters are provided in the above-described distortion removal loop, and the frequency characteristics of the filters in the distortion removal loop are changed by the phase and amplitude of the frequencies of the vector adjuster and the main amplifier. A feedforward amplifier characterized by flattening the phase and amplitude characteristics of the entire distortion removal loop by making the characteristics opposite to the characteristics.

[0020]

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

FIG. 1 shows a configuration of a feedforward amplifier according to a first embodiment of the present invention. The configuration and the operation will be described below.

The input signal 1 is divided by the directional coupler 2 into the main amplifier 4 and the filter 6 of the detection loop which replaces the conventional delay line.

On the main amplifier 4 side, the input signal 1 first has a pilot signal 10 inserted, passes through a vector adjuster 3 composed of a variable phase shifter and a variable attenuator, and is amplified by the main amplifier 4. At this time, distortion occurs. Then, the signal is transmitted to the signal combining unit 7 of the directional coupler 5.

On the other hand, the filter 6 on the other detection loop side
The input signal 1 passes through the filter 6 and is transmitted to the signal synthesizing unit 7.

In the signal synthesizing section 7, the phase of the filter 6 and the phase of the main amplifier 4 are shifted by 180 degrees, and the vector adjuster 3 is adjusted in order to make the signal amplitude the same.
Set to minimize the signal level.

For example, the variable phase shifter and the variable attenuation of the vector adjuster 8 are adjusted so that the input pilot signal 10 is minimized.

Therefore, the output from the signal synthesizer 7 is dominated by the amount of distortion in the main amplifier 4, and is amplified by the auxiliary amplifier 9 through the vector adjuster 8 in the distortion detection loop.

On the other hand, the signal from the main amplifier 4 passes through the directional coupler 5, passes through a filter 11 of a distortion removal loop instead of a conventional delay line, and is transmitted to the signal combining unit 13 of the directional coupler 12. You.

The phase and attenuation of the vector adjuster 8 are adjusted so that the signal synthesizer 13 cancels the distortion.
It is configured to extract the least distorted signal.

Incidentally, in the high power main amplifier 4 and the like used in the feedforward amplifier which is a linear amplifier, deviations of the phase and the output level occur within the frequency band used, and a wave between the frequency and the phase and amplitude characteristics. It has a type-like correlation.

FIG. 3 shows an example of the above characteristics. As the frequency characteristics of the main amplifier 4, the phase is shown in (a) and the amplitude is shown in (b).
In (a), the output of the main amplifier 4 is operated at 43 dBm, and the phase at that time is set to zero degree with 2 GHz as a reference frequency. At 1.8 GHz, the phase angle is +5 degrees;
At 2 GHz, it was -5 degrees.

Further, as shown in FIG. 3B, the output of the main amplifier 4 is operated at 43 dBm, and
Is used as a reference frequency, and the amplitude value at that time is set to zero. 1.
At 8 GHz, the amplitude value is +2 dB, and at 2.2 GHz, -2 dB.
dB.

In a conventional feedforward amplifier using the output of the main amplifier 4 at around 43 dBm, in the conventional method using the delay line 26 and the delay line 30 as shown in FIG. It has a very disadvantageous effect on the amount of distortion improvement.

In general, when operating as a feedforward amplifier, the amount of distortion suppression should be 30 dBc within the used band.
In order to ensure the above, the deviation of the amplitude and the phase is 0.5
It must be within dB and within 2 degrees.

For example, ± 200 MHz around a frequency of 2 GHz
In order to secure the wide band, it is necessary to flatten the phase and amplitude frequency characteristics shown in FIGS. 3 (a) and 3 (b) as much as possible. The main cause of this frequency characteristic is the main amplifier 4.

Therefore, for that purpose, the main amplifier 4 is set to 43 dB
At the time of high output such as m, a plurality of filters 6 are inserted in parallel so that the characteristics of the frequency and the phase and the amplitude are opposite to each other, and the phase and the amplitude characteristics are flattened with respect to the frequency.

That is, in order to improve the amount of distortion suppression, a flattening filter having phase and amplitude characteristics is set in the feedforward amplifier circuit with characteristics suitable for the distortion detection loop side and the distortion removal loop side in the circuit. I do.

FIG. 4 shows a configuration for flattening the phase and amplitude characteristics. For example, a three-stage band-pass filter as shown in FIG. The first band-pass filter No. 1 is set, and a filter having a pass band width of 2.0 GHz to 2.2 GHz is used. Next, a second band-pass filter No. 2 is set, the pass bandwidth is from 1.9 GHz to 2.1 GHz, and the amplitude loss of the pass band is No.
A filter that attenuates 0.5 dB larger than the amplitude loss in the pass band of one filter is set.

The third band pass filter No. 3
Is set so that the pass band width is from 1.8 GHz to 2.0 GHz, and the amplitude loss of the pass band is attenuated 0.5 dB larger than the amplitude loss of the pass band of the No2 filter. The amplitude characteristic at this time is shown in FIG. The frequency characteristics when the above filters are configured in parallel are shown in FIG. As described above, the characteristic and the phase in which the signal is not attenuated as high as the high frequency are opposite to the phase of the main amplifier 4. If the filter 6 having the three-stage configuration is replaced with the delay line 26 of the feedforward amplifier in FIG. 2, the phase and amplitude of the detection loop can be flattened.

Although this configuration has a three-stage configuration in the above description, the phase and amplitude can be increased or decreased as long as the characteristics of the detection loop can be canceled and flattened. Therefore, the number of stages can be configured with n stages (n ≧ 1).

Although the configuration example of the filter has been described with reference to the distortion detection loop, the same can be applied to the distortion removal loop. That is,
A plurality of filters 11 are inserted in parallel so as to cancel the frequency characteristics of the auxiliary amplifier 9 so that the characteristics of the frequency and the phase and the amplitude of the auxiliary amplifier 9 are in opposite phases. Was made flat.

Further, in this embodiment, the output power of the main amplifier is 43 dBm, but the same result can be obtained even at 46 dBm, and therefore, it is possible to cope with 40 W or more.

In the above embodiment, the filter is set at the position shown in FIG. 1. For example, the position of A and B before and after the main amplifier 4 and the position before and after the auxiliary amplifier 9 for phase and amplitude adjustment. Positions of C and D, and vector adjuster 3
And the positions of E and A before and after F, and F and
Even if it is inserted at the position C, the amount of distortion of the output signal 14 can be minimized.

In order to minimize the amount of distortion, the phase and attenuation of each vector adjuster can be automatically adjusted.

[0045]

As described above, in the feedforward amplifier of the present invention, even when the output power is 10 W or more,
In order to obtain frequency characteristics that cannot be controlled by the variable phase shifter and the variable attenuator, it is possible to secure a distortion suppression amount of 40 dBc or more with a bandwidth of 60 MHz or more even at a high frequency of 2 GHz or more using a filter. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a feedforward amplifier according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a feedforward amplifier in a conventional example.

FIG. 3 is a diagram illustrating phase and amplitude characteristics of a main amplifier.

FIG. 4 is a diagram illustrating phase and amplitude characteristics of a filter. (A) Three-stage configuration diagram of the filter (b) N-stage configuration diagram of the filter (c) Frequency pass amplitude characteristics in the three-stage configuration of the filter (d) Amplitude characteristics of the filter

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input signal 2 directional coupler 3 vector adjuster 4 main amplifier 5 directional coupler 6 filter 7 signal synthesizer 8 vector adjuster 9 auxiliary amplifier 10 pilot signal 11 filter 12 ... Directional coupler 13 ... Signal combiner 14 ... Output signal 20 ... Pilot signal 21 ... Input signal 22 ... Directional adjuster 23 ... Vector adjuster 24 ... Main amplifier 25 ... Directional coupler 26 ... Delay line 27 ... Signal Combining unit 28 ... Vector adjuster 29 ... Auxiliary amplifier 30 ... Delay line 31 ... Signal combining unit 32 ... Output signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Kosugi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A first vector adjuster having a first phase shifter, a first attenuator, a distortion detection loop having a main amplifier, and a second phase adjuster having a second phase shifter and a second attenuator. A vector adjuster and a distortion removal loop having an auxiliary amplifier;
A pilot signal generator and a pilot detector for detecting the pilot signal, wherein the distortion removal loop is connected after the distortion detection loop, and the distortion generated in the main amplifier is extracted by the distortion detection loop; After being amplified by the auxiliary amplifier, the output of the main amplifier is re-injected in the opposite phase of the amplitude, the distortion component of the main amplifier is canceled out, and a foot forward amplifier for performing distortion compensation, wherein the distortion detection loop or the A feed-forward amplifier, wherein a filter is provided in a distortion removal loop, and a plurality of the filters are set in parallel with respect to a signal line. 2. A distortion detection loop comprising a plurality of filters, wherein a frequency characteristic of the filter in the distortion detection loop is opposite to a frequency phase and amplitude characteristic of the vector adjuster and the main amplifier. 2. The feedforward amplifier according to claim 1, wherein the phase and amplitude characteristics of the entire distortion detection loop are flattened. 3. A characteristic in which a plurality of filters are provided in the distortion removal loop, and a frequency characteristic of the filter in the distortion removal loop is opposite to a frequency phase and amplitude characteristic of the vector adjuster and the main amplifier. 2. The feedforward amplifier according to claim 1, wherein the phase and amplitude characteristics of the entire distortion removal loop are flattened.