JPS6278902A - High output amplifier with linearized circuit - Google Patents

Abstract

PURPOSE:To obtain a necessary high output from a small-scale high power amplifier(HPA) and to realize an unmanned earth station by by receiving the output signal of the 1st detector and the output signal of the 2nd detector and generating a voltage corresponding to the amplitude difference between both signals, and applying it as a control signal to a variable attenuator. CONSTITUTION:The vector modulators(V.M.) consisting of two components, i.e. a variable attenuator 7 and a phase shifter 9 are brought under negative feedback control and then one fine part signal 104 of the output of an HPA 1 which is led out by a coupler 2 is controlled to the same amplitude and phase with the output of a delay device 3. The delay device 3 compensates signal delay caused in the V.M. and HPA 1, but the V.M. and HPA 1 normally have a wide band, so the quantity of the delay is small. Thus, an output signal 103 becomes invariably in phase with an input signal 101 and the HPA 1 is linearized. For the purpose, the amplitudes and phases of the input and output signals of the HPA are detected directly, and distortion control is performed through a negative feedback loop on the basis of the result, so that accurate distortion corrections are made.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is applied to a high power amplifier mainly used in a small earth station for satellite communication.
r: Linearizer (hereinafter referred to as HPA)
It is related to.

(Prior Art) Satellite communication allows a wide area communication network to be constructed using a single satellite, and is particularly suitable for mobile communication and small-capacity communication in remote mountainous areas, remote islands, etc. However, for such small satellites, how to overcome the large attenuation of signal power due to the long distance to the satellite is a serious problem. Small scale H
In order to secure the necessary output power for the PA, H
PA must be used in or near the saturated region,
Suppression of nonlinear distortion, that is, linearization of HPA, becomes an important technical issue. An example of a conventional linearization circuit is shown in FIG. 2, where 1 is an HPA, 11 is a π/2 phase shifter, 12 is a compensation nonlinear circuit, and 13 is an RF signal synthesizer. The operation of this circuit is π/2
Phase shifter 11. Compensation nonlinear circuit 12. RF signal synthesizer 1
This method is called a pre-distortion method, in which an inverse nonlinear characteristic is added to the signal in advance so as to compensate for the nonlinear distortion of HPAI using a compensation circuit consisting of three components.

FIG. 3 shows another example of a conventional linearization circuit, in which 2 is a directional coupler, and 3 is a delay device that compensates for the signal delay of the HPA. 21 is a hybrid that outputs an error signal obtained by vectorially subtracting the output of coupler 2 from the output of delay device 3; 22 is a high-output error amplifier that amplifies the output of hybrid 21; and 23 is a high-output error amplifier that amplifies the output of coupler 2.
This is an RF synthesizer that adds the output of the error amplifier 22 and the output of the error amplifier 22.

By accurately setting the attenuation and phase characteristics of the circuit, a distortion component is obtained in the output of the hybrid 21, which is amplified by the error amplifier 22, and the main signal output (high If the output/phase relationship between the power output side) and the 0 circuit that performs RF synthesis is accurate, distortion components are canceled in the RF synthesizer 23, and linearization can be realized.

(Problems to be Solved by the Invention) However, the bridistortion method is an open-loop control, and cannot compensate for distortion fluctuations caused by temperature fluctuations or temporal fluctuations in the HPA, and also cannot compensate for nonlinear distortion during operation. There is a problem in that it is impossible to monitor.

In addition, since the method shown in FIG. 3 is basically open-loop control, it is not only impossible to compensate for temperature and temporal fluctuations in each part, but also the error amplifier 22 is required to have good linearity. This had the disadvantage of making the circuit complicated.

There is also the problem that loss of signal power in the RF combiner 23 is also unavoidable.

An object of the present invention is to improve linearity by using closed-loop negative feedback control in view of the problems in the prior art described above, thereby eliminating the need for a large power amplifier such as the error amplification device in the linearization circuit itself, and eliminating the need for a high power amplifier such as the error amplification device described above. It is an object of the present invention to provide a high-output amplifier having a linearization circuit capable of compensating for variations in linearity caused by temperature fluctuations and changes over time.

Means for Solving Problems) The present invention has the following configuration to achieve the above object. That is, the high-output amplifier with linearization circuit of the present invention includes: an amplifier; and a variable amplifier that is provided between an external input terminal into which a signal to be amplified is input and an input terminal of the amplifier and whose attenuation amount can be changed by a control voltage. a cascade circuit consisting of an attenuator and a variable phase shifter whose phase shift can be changed by a control voltage; a directional coupler inserted on the output side of the amplifier; a delay circuit connected to the external input terminal; a phase comparator that receives an output signal from a coupling output terminal of a directional coupler and an output signal from the delay circuit, generates a voltage according to the phase difference between the two signals, and applies the voltage to the variable phase shifter as a control voltage; a first detector that receives a signal from the coupling output end of the directional coupler and performs amplitude detection; a second detector that receives an output signal from the delay circuit and performs amplitude detection; and the first detector. a voltage difference detector which receives the output signal of the detector and the output signal of the second detector, generates a voltage according to the amplitude difference between the two signals, and applies it to the variable attenuator as a control voltage; do.

(Function) The function of the high-output amplifier with linearization circuit of the present invention will be explained below based on the configuration block diagram of the embodiment.

Fig. 1(a) is a block diagram showing the configuration of an embodiment of the present invention, and Fig. 1(b) is a vector diagram explaining the operation. , 3 is a delay device, 4 and 5 are square law detectors, 6 is a voltage difference detector, 7 is a variable attenuator whose voltage can be controlled externally, 8 is a phase comparator, and 9 is a variable phase shifter whose voltage is controllable. It is.

The operation of the linearizer according to the present invention will be explained with reference to FIG. 1(b).The circuit is a vector modulator (Vector
Modulator (hereinafter referred to as V, M)) is taken out by the coupler 2 by applying negative feedback control.
Control is performed so that one minute partial signal 104 of the output of the PAI has the same amplitude and phase as the output of the delay device 3. The delay device 3 compensates for the signal delay occurring in V, M, and HPA1, but since V, M, and HPAI usually have a wide band, the amount of delay is small.
is a signal that always has the same shape as the input signal 101, and HPAl is linearized. An analytical explanation is given below. The gold input signal 101 is set to Vl, and the following formula (1) is used. Now, the gain of the variable attenuator 7 is set to Gl, the phase shift amount of the variable phase shifter 9 is set to φ, and the output signal 102 of the variable phase shifter 9 is If it is ■1', then V1'=G+A(t)cos (θ+(1)-φ)−-
--(2>). Furthermore, if the HPAI gain is GA, the phase shift is θ, and the HPAI output signal 103 is Vo, then Vo = GA-G+A(t)Cos (θ+(1)-
φ−θ)−(3) However, since GA and θ are nonlinear distortions, their values change depending on the input signal level.

The directional coupler 2 sets the combined output level of the combined output 104 to a small value so that power loss in the main signal output 105 can be almost ignored. If it is 1/L and the signal 104 at the coupled output end of the directional coupler 2 is VC, then (2). (1)=GLG, A(t) cos (θ+(1
)-φ-θ)--(4) This signal is applied to the square law detector 5 and the phase comparator 8. On the other hand, delay device 3
The output of is applied to a square law detector 4 and a phase comparator 8.

The delay time of the delay unit 3 is determined by the variable attenuator 7. If the delay times are set equal to the sum of the delay times of variable phase shifter 9 and HPAI, the operations of voltage difference detector 6 and phase comparator 8 can be calculated in the same way as when the delay times are all zero.

Since Equation (4) does not include a delay time term, the delay time of the delay device 3 is now calculated as zero. Therefore, the output of detector 5 ■. d and the output ■Id of the detector 4 are respectively v ad =GLa l A ---m-
−−−−−<4°)V+a=A −
-1----(1') Therefore, since the output voltage of the voltage difference detector 6 is the difference between equation (4') and equation (l'), on the other hand, the position of va(t) and Vl is The phase difference is equation (4) and equation (1)
Therefore, the output voltage VB of the phase comparator 8 is: VB=sin(φ+θ) −−−−−−(6)
becomes.

The gain G when the above V^ is added as the control voltage of the variable attenuator 7 is G + = G +. -KAVA---
--------(7). However, G1° and KA are constants, G1° is the gain when V=0, and KA is the loop gain of the amplitude control loop. In addition, the above VB is set to the variable phase shifter 9.
The phase amount φ when added as the control voltage of
) and formula (7) - 6A (KA) 1) --1 --- (9) and formula (6)
From equation (8), φ=-'' set −θ 1 +Ke 〜−θ (KB)1) −−−−(
10), and by substituting equations (9) and (10) into equation (3) to obtain the HPAI output signal 103, V□ =
GA-GIA(t) cos (θ+(1)-φ-
θ)+LA(t) cos θt(t) −
m-(11), and it can be seen that it operates as a linear amplifier with a constant gain.

As can be seen from the above description, the present invention directly detects the amplitude and phase of the input and output signals of the HPA, and based on the results, performs distortion control using a negative feedback loop, making it possible to perform accurate distortion correction. can.

In the present invention, since the signal to be amplified is a high-level signal for transmission, there is no need to worry about the influence of thermal noise. Therefore, the loop bandwidth of the feedback loop can be set sufficiently wide, and high-speed tracking operation can be performed. It is possible to make it happen.

Normally, the frequency bandwidth of HPA is extremely wide (for example, 500 MHz), whereas the signal speed of small-capacity stations is extremely low (64 Kb/s to 2 Mb/s), so a sufficiently high-speed control loop is required for the signal. Can be set.

(Effects of the Invention) Since the high-output amplifier with a linearization circuit of the present invention has the configuration and operation described above, it can eliminate HP caused by temperature fluctuations and changes over time without using a high-power amplifier in the linearization circuit itself.
There is an advantage that variations in the linearity of A can also be compensated for.

Furthermore, there is an advantage that nonlinear distortion can be constantly monitored by detecting a signal from an appropriate location in a closed-loop control loop.

As a result, the necessary high output can be obtained with a small-scale HPA, and the earth station can be unmanned, reducing the construction and maintenance costs of the earth station, thereby creating a satellite communication network that connects more earth stations. It has the advantage that it can be constructed.

[Brief explanation of drawings]

FIG. 1 is a block diagram and an operation explanatory vector diagram showing the configuration of an embodiment of a high-output amplifier with a linearization circuit of the present invention, and FIG. 2 is a block diagram showing the configuration of a first example of a conventional linearization circuit.
FIG. 3 is a block diagram showing the configuration of a second example of a conventional linearization circuit. 1...HPA, 2...Directional coupler), 3...Delay device, 4,5...
... Square law detector, 6 ... Voltage difference detector, 7
....variable attenuator, 8 ....phase comparator,
9...variable phase shifter, 11...π/2
Phase shifter, 12... Compensation nonlinear circuit, 13
...RF signal synthesizer, 21...Hybrid, 22...High output error amplifier, 2
3...RF synthesizer. Agent Patent Attorney Yoshihiro Yahata / Figure Conventional #$ conversion episode ((70th fall) A Wei Ei 2 Kuchitsuo/l Heki 1st conversion episode title error (2nd evening) 1) Shyness figure 3

Claims (1)

[Claims] Amplifier: A variable attenuator whose attenuation can be changed by a control voltage, and a variable shifter whose phase shift can be changed by a control voltage, which are provided between an external input terminal into which a signal to be amplified is input and an input terminal of the amplifier. a cascade circuit consisting of a phase shifter; a directional coupler inserted into the output side of the amplifier; a delay circuit connected to the external input terminal; an output signal from the coupling output terminal of the directional coupler; a phase comparator that receives the output signal from the delay circuit, generates a voltage according to the phase difference between the two signals, and applies it to the variable phase shifter as a control voltage; The first step is to detect the amplitude using
a second wave detector that receives the output signal from the delay circuit and performs amplitude detection; a second wave detector that receives the output signal of the first wave detector and the output signal of the second wave detector and detects the amplitude of both signals. A high-output amplifier with a linearization circuit, comprising: a voltage difference detector that generates a voltage according to an amplitude difference and applies it to the variable attenuator as a control voltage.