JPS62604B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compensation circuit for a linear amplifier having gain fluctuation and amplitude nonlinearity.

In general, a linear amplifier refers to an amplifier with a linear input-output relationship, and it amplifies the voltage, current, or power applied to the input terminal by a factor of 2. However, in actual linear amplifiers, the active elements used are non-linear. Due to the influence of the characteristics and the elements constituting the circuit, there is a difference in gain depending on the magnitude of the input signal, that is, there is nonlinearity, and this causes intermodulation distortion. Class AB linear power amplifiers designed to obtain large output power have large nonlinearities, and when amplifying signals that have undergone amplitude modulation, distortion occurs in the output envelope and generates unnecessary waves near the signal frequency. Furthermore, since the gain of the linear amplifier changes due to changes in temperature, power supply voltage, etc., undesirable output fluctuations occur.

By focusing on the fact that when the gain of a linear amplifier is constant, the output envelope and the input envelope show a similar shape with a constant ratio (gain), by detecting and comparing these input and output envelopes, Detects the change in gain of a linear amplifier with gain fluctuation, and controls the gain of a voltage-controlled variable gain amplifier installed on the input side of the linear amplifier to compensate for the fluctuation gain of the linear amplifier.
The envelope feedback circuit attempts to improve the defects of the linear amplifier by keeping the gain of the amplifier circuit constructed by the cascade connection of the variable gain amplifier and the linear amplifier constant and approaching the ideal amplifier.

Figure 1 is a block diagram of a conventional envelope feedback circuit, where 1 is a linear amplifier with gain variation and the gain is A, 2 is an input detector and the efficiency is d ₁ , 3 is an output coupler and the degree of coupling is b, 4 is the output side detector and the efficiency is d ₁ , 5
is a differential amplifier with a gain of a ₂ , and 6 is a voltage-controlled variable gain amplifier with a sensitivity of a ₁ .

However, since the differential amplifier 5 and variable gain amplifier 6 operate with small signals, linearity is good and d ₁ , d ₂ ,
It is assumed that b, a ₁ , and a ₂ are constants and do not vary, and only A varies.

Now, the input voltage V _i of the variable gain amplifier 6, the input voltage V _i ' of the linear amplifier, and the output voltage V of the linear amplifier
_p , the error voltage V _e of the differential amplifier output, and the gain setting voltage of the variable gain amplifier Co. When the output side detector 4 detects the error voltage Ve and inputs it to the differential amplifier 5, and the differential amplifier 5 detects the error voltage Ve and controls the variable gain amplifier 6 together with the gain setting voltage Co, the following equation is obtained. To establish.

Vi′=a ₁ (Ve+Co)Vi……(1) formula Vo=Vi′A……(2) formula Ve=a ₂ d ₁ (Vi′−Vob)……(3) formula (1) ~ According to formula (3), Vo=a ₁ ACo/1-a ₁ a ₂ d ₁ V ₁ (1-bA)・
Vi...Equation (4) Let Gv be the voltage gain of the amplification system due to the cascade connection of the variable gain amplifier 6 and the linear amplifier _1.Gv = V _p /V _i =a ₁ AC _p /1 - a ₁ a ₂ d _{1 Vi}
(1-bA)......Equation (5) If we want to make G _v independent of the variable gain A of the linear amplifier, a ₁ a ₂ d ₁ V _i = 1 ......Equation (6). G _v =a ₁ C _p /b (7), and since a ₁ , b, and C _p are constants, G _v is a constant, that is, constant. However, since Equation 6 includes V _i , which is the input voltage of the system and is a variable, Equation (6) is satisfied only when the input voltage V _i is a certain value, and (7)
The formula does not hold.

In other words, in the circuit shown in Figure 1, an amplification system in which a specific output is always obtained at a specific value of the input voltage V _i can have the effect of keeping the gain of the system constant and preventing output fluctuations, but it is susceptible to amplitude modulation. In an amplification system that linearly amplifies a signal, the input voltage changes, so
There is a drawback that the gain _Gv of the system cannot be made constant, and the nonlinearity of the linear amplifier 1 cannot be improved.

The present invention eliminates these drawbacks of conventional circuits and corrects the gain of a linear amplifier so that it is always a constant value. By correcting this gain to a constant value, the non-linearity of a linear amplifier is The purpose of this is to significantly improve performance, intermodulation distortion, output fluctuations caused by gain fluctuations due to temperature and power fluctuations, characteristic changes due to deviations in amplifier components, efficiency, etc.

FIG. 2 shows an embodiment of the present invention. 1 is a linear amplifier with gain variation and the gain is A, 2 is the input side detector of linear amplifier 1 and the efficiency is a ₁ , 3 is the output signal coupler and the degree of coupling is b, and 4 is the output side detection of linear amplifier 1. The efficiency is d ₁ in the amplifier, the gain is a ₂ in the differential amplifier, 6
is a voltage controlled variable gain amplifier with sensitivity a ₁ . The above is the same configuration as in Figure 1, and then 7 is a divider with a gain of a ₃ , 8 is a differential amplifier with a gain of a ₄ , and 9 is an input detector of the variable gain amplifier 6 with an efficiency of d ₂ . However, since the differential amplifier 5, variable gain amplifier 6, divider 7, and differential amplifier 8 operate with small signals, linearity is good and d ₁ , d ₂ , b, a ₁ , a ₂ , a ₃ , a ₄ are constants and do not vary, and only A varies.
Now, the input and output envelopes of the linear amplifier 1 are detected via the input side detector 2, output signal combiner 3, and output side detector 4, and the error is calculated by comparing and subtracting them with the first differential amplifier 5. Obtain the voltage V _e .

Here, d ₁ , b, and a ₂ are constants, so if A fluctuates, a fluctuation appears in V _e . Since V _e is a function of the input voltage Vi as shown in equation (3),
In order to make it independent of V ₁ , the envelope of the input voltage Vi is detected by the variable gain amplifier input detector 9,
Obtain the gain setting DC voltage V _c and then divide V _e by V _c using the divider 7 to obtain the compensation signal voltage V _n
get. Further, a gain setting DC voltage V _c is applied by the second differential amplifier 8 to obtain a variable gain amplifier input signal voltage V _n '. Next, change the variable gain amplifier 6 to V
By controlling _n ′, the linear amplifier input voltage V
_i ′ is obtained.

These can be expressed numerically as follows.

The output V _p of the linear amplifier 1 is V _p =V _i ′A (8) The output Ve of the differential amplifier 5 is calculated from the difference between the input and output of the linear amplifier 1 as Ve=a ₂ , d ₁ (Vi′ -Veb) ......Equation (9) The output Vc of the variable gain amplifier input detector 9 is Vc = d ₂ Vi ......Equation (10) The output Vm of the divider 7 is Vm = a ₃ Ve/Vc ... (11) The output Vm' of the differential amplifier 8 is Vm' = a ₄ (Co - Vm) (12) Therefore, the output Vi' of the variable gain amplifier 6 when receiving feedback is Vi' =a ₁ Vm'Vi......Equation (13) Here, from Equations (11) and (12), Vm'=a ₄ (Co-a ₃ Ve/Vc......Equation (14) (13), (14) ) Vi′=a ₁ a ₄ (Co−a ₃ Ve/Vc)Vi……(15) From equations (8) and (15), Vo=a ₁ a ₄ A(Co−a ₃ Ve/Vc )Vi...(16) From equations (16), (9), and (10) Solving equation (17) for Vo, we get Here, if the voltage gain is Gv when the entire amplification system consisting of the variable gain amplifier 6 and the linear amplifier 1 connected in series in Fig. 2 is considered as an amplifier, then Gv=Vo/Vi......Equation (19) Therefore, from equations (19) and (18) holds, and equation (20) is not a function of the input voltage Vi, which is a variable.

Here, in order to make Gv independent of the varying gain A of the linear amplifier, each constant is determined as shown in the following equation.

−a ₁ a ₂ a ₃ a ₄ d ₁ / d ₂ = 1 (21) Since a ₁ , a ₂ , a ₃ , a ₄ , d ₁ , and d ₂ are constants, (21 ) In order to satisfy the equation, it is easy to adjust one part.

Substituting equation (20) into equation (21) results in Gv=a ₁ a ₄ Co/b......(22), and Gv becomes only the constants of a ₁ , a ₂ , b, and C _p , It becomes a constant value that is completely unrelated to variables A and Vi. In other words, when the entire system is considered as an amplifier, it becomes an ideal amplifier with constant gain even if it has a non-linear amplifier with gain variation inside. Also, since Co is a DC voltage value, by varying this,
It becomes a voltage-controlled variable gain amplifier that can freely vary the gain of the entire system.

As explained above, when envelope feedback is applied to a linear amplifier with gain variation using the circuit system of the present invention, the amplifier becomes an ideal amplifier, and the nonlinearity of the amplifier
Intermodulation distortion, output fluctuations caused by gain fluctuations due to temperature and power supply fluctuations, characteristic changes due to deviations in amplifier components, etc. are greatly improved, and efficiency is also improved by increasing voltage utilization without distortion. This results in
It has the advantage of improving the performance of electron tube type and semiconductor type power amplifiers that amplify signals that have undergone various amplitude modulations such as DSB, SSB, and ISB.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional envelope feedback circuit.
FIG. 2 is a block diagram of an envelope feedback circuit according to the present invention. 1... Linear amplifier, 2... Input side detector, 3...
...Output coupler, 4...Output side detector, 5, 8...
Differential amplifier, 7... Divider, 6... Voltage controlled variable gain amplifier, 9... Reference input detector.

Claims (1)

[Claims] 1. A voltage-controlled variable gain amplifier that varies the amplitude of an input signal, a linear amplifier that amplifies the signal from the voltage-controlled variable gain amplifier, an input-side detector that detects the input envelope of the linear amplifier, and the linear amplifier. an output side detector for detecting the output envelope of the output side detector, and a differential amplifier that receives the outputs of both input and output side detectors, detects an error thereof, and feeds it back to the voltage controlled variable gain amplifier. The envelope feedback circuit includes a divider that divides the error obtained from the input and output envelopes of the linear amplifier by the input envelope of the voltage controlled variable gain amplifier, and a gain setting DC voltage is applied to the output from the divider. In addition, a differential amplifier is provided which feeds back this to the voltage controlled variable gain amplifier, and the input amplitude of the linear amplifier is corrected by the output of the differential amplifier, and the voltage controlled variable gain is adjusted regardless of the gain of the linear amplifier. An envelope feedback circuit characterized in that the gain between an amplifier and a linear amplifier output is kept constant.