JPS60146512A - Automatic gain control method - Google Patents

Abstract

PURPOSE:To obtain an automatic gain control method with less distortion of the amplitude of an input signal even with a wide dynamic range by changing a feedback coefficient based on a control signal. CONSTITUTION:An output signal X' is applied with absolute value processing by an absolute value circuit 2 and a difference with a reference signal Ref is obtained by an adder 3. The difference and the feedback coefficient delta are multiplied by a multiplier 4, its result is added with an output of an integration device 6 at an adder 5, the timewise mean value is obtained and multiplied and added with prescribed coefficients K, L so as to obtain a control signal alpha. An input signal X is multiplied with the control signal alpha at a multiplier 1 and the output X' is obtained. The control signal alpha is fed also to a multiplier 9, where the signal is multiplied with a coefficient beta so as to obtain said feedback coefficient delta. As a result, the entire loop gain is not changed so much to the input change and almost uniformed, then the distortion of amplitude is less even with a wide dynamic range.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an automatic gain control method for making the input level of a signal transmitted via a line etc. uniform, and in particular, it relates to an automatic gain control method for making the input level of a signal transmitted via a line etc. This invention relates to an automatic gain control method that can minimize deterioration in the amplitude direction.

[Technology background]

Generally, signals transmitted through lines are distorted and the input level changes, so an automatic gain control circuit is used to equalize the input level, and is widely used in modems, etc. has been done.

[Conventional technology and problems]

In the conventional automatic gain control method, as shown in the explanatory diagram of FIG. 1, the input signal X is multiplied by the control voltage α in a multiplier 1, and the output signal
I try to get the following. This control voltage α is created by a feedback loop as follows. The output signal X' is made into an absolute value by an absolute value circuit 2, and this is subtracted as a negative signal AX' from the reference voltage Ref by an adder 3, and further multiplied by a feedback coefficient δ by a multiplier 4 to obtain a feedback amount. This feedback amount is added to the integral value (tap value) T of the integrator 6 in the adder 5, averaged, and then multiplied by a predetermined coefficient K in the multiplier 7.
are added to create the control voltage α.

That is, the control voltage α is expressed by the following formula, α=(δ(Ref-AX')+T)K+L (1) The feedbank amount is adjusted by the feedbank coefficient δ and then averaged, and the averaged voltage is obtained by multiplying and adding L to a predetermined coefficient.

According to this automatic gain control operation, the integral value (tap value) T
The relationship between and the control voltage α is as shown in Figure 2, and as the tap value increases, the control voltage α also increases, and conversely, the input voltage
Since the input voltage X' is fed as a negative feedbank, the relationship between the control voltage α and the input voltage Even if the input voltage changes, an output voltage of a uniform level can be obtained. At this time, the loop gain of automatic gain control (AGC) is given by the slope (differential value) of the curve in Figure 2, as shown in Figure 3, in relation to the tap value, so the larger the tap value T is, the more becomes smaller. Since this difference in tap value T is due to a difference in input level, the AGC loop gain differs depending on the input level. If this loop gain is large, distortion will occur in the amplitude direction of the input signal. Therefore, in the conventional automatic gain control method, when the dynamic range of AGC is wide, the difference in the loop gain with respect to the input level becomes large, resulting in distortion in the amplitude direction of the input signal. The problem is that the degradation becomes unacceptable, making it impossible to widen the dynamic range.

[Purpose of the invention]

The purpose of the present invention is to achieve a wide dynamic range,
An object of the present invention is to provide an automatic gain control method that reduces distortion in the amplitude direction of an input signal.

[Structure of the invention]

To achieve the above object, the present invention provides an automatic gain control method in which an input signal is multiplied by a control signal to obtain a uniform output signal in a predetermined dynamic range regardless of changes in the input signal. a step of obtaining a feedback amount by multiplying the difference between the reference signal and the absolute value output signal by a feedbank coefficient; and obtaining an average value obtained by averaging the feedbank amount over time to control the control. The method is characterized by comprising a step of determining a signal, and a step of changing the feedback coefficient based on the control signal.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 4 is a detailed explanatory diagram of the present invention, and shows the method of the present invention in a model manner. In the figure, the same parts as in Figure 1 are indicated by the same symbols, 9 is a multiplier, and the control voltage α
and a predetermined coefficient β to output a feedback coefficient δ.

Incidentally, the coefficient β is made small because it would be too large if the control voltage α was directly used as the feedback coefficient δ.

In the present invention, the feedback coefficient δ, which is a fixed value in conventional control methods, is made variable as a function of the control voltage α.

That is, the function of tap value T versus control voltage α in FIG.
Since the relationship between the tap value T and the loop gain G shown in the figure shows opposite characteristics, if the feedback coefficient itself that controls the feedbank amount is changed according to the characteristics shown in FIG. 2, the loop gain G becomes uniform.

Therefore, in the present invention, the feedbank amount is controlled by the control voltage α
In order to change the feedback coefficient δ according to the control voltage α, the feedback coefficient δ is changed according to the control voltage α.

As a result, the new loop gain G becomes as if the characteristics in FIG. 3 were corrected by the characteristics in FIG. 2, and as shown in FIG.
The loop gain G becomes substantially uniform with respect to the tap value T. This reduces distortion in the amplitude direction even with a wide dynamic range.

FIG. 6 is a configuration diagram of an embodiment for realizing the method of the present invention. In the figure, 11 is an analog-to-digital conversion circuit (hereinafter referred to as an AD converter), which converts an analog input signal into a digital input signal 2 is a signal processor (hereinafter referred to as SPU) that performs the above-mentioned automatic gain control by calculation from the input signal is a register which serves as a buffer for storing the output signal X' obtained by the calculation in 5PUI 1 and supplying it to other automatic equalizers, etc.

Next, the operation of the embodiment shown in FIG. 6 will be explained. .

The analog input signal is converted into a digital value at a predetermined period by an AD converter, and is input to the 5PUI 2. 5PUI
2 reads this at a predetermined cycle, reads out the control voltage α(t-1) calculated in the previous cycle from the memory 13, and obtains the output signal X' (t) from the following equation.

X' (t)=X (t) · α (t-1) (2) This output signal X' (t) is output to the register 14 and made available to other circuits. This output signal x' (t) is then converted into an absolute value by the 5PU12 and becomes AX'.

Further, the voltage is stored in the memory 13 and subtraction is performed between it and the reference voltage Ref. Furthermore, the control voltage α obtained from the previous calculation
(t-1) is multiplied by β, and the feed bank coefficient δ(1
) is obtained from the following formula.

δ(t)=β·α(t-1) (3) Multiply this δ(1) by the above-mentioned subtraction result to obtain the feed bank amount. 5
The PU 12 adds this to the previous integral value T(t-1) and stores the added value in the memory 13 as a new integral value T(t). 5PUI 2 multiplies this added value by the coefficient K, further adds the coefficient to this, obtains the control voltage α(1), stores it in the memory 13, and outputs the next input signal X(
t+1)) (second equation). By repeating this at a predetermined period, automatic gain operation is performed for each analog signal.

The same effect can be achieved by using an analog circuit in addition to the digital AGC circuit described above, and a digital AGC circuit can also be constructed by combining individual multipliers in place of the 5 PUI 2.

Although the present invention has been described above using one embodiment, the present invention can be modified in various ways according to the gist of the present invention, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, in an automatic gain control method that multiplies an input signal by a control signal to obtain a uniform output signal in a predetermined dynamic range regardless of changes in the input signal, the output signal is a step of obtaining a feedback amount by multiplying the difference between the reference signal and the absolute value output signal by a feedbank coefficient; and obtaining an average value obtained by averaging the feedbank amount over time to control the control. Since the method is characterized by comprising a step of determining the signal and a step of changing the feed bank coefficient based on the control signal, the amount of feedback is changed according to the magnitude of the control signal, and thereby the AGC This has the effect of making the loop gain uniform, thus reducing distortion in the amplitude direction over a wide dynamic range, improving signal fidelity and widening the dynamic range.

Furthermore, it is easy and simple to achieve this, and it also has a practical effect that such excellent functions can be provided at low cost.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the conventional automatic gain control method, Fig. 2 is a tap value vs. control voltage characteristic diagram according to the conventional method, Fig. 3 is a loop gain characteristic diagram according to the conventional method, and Fig. 4 is a diagram showing the characteristics of the control voltage according to the conventional method. A detailed explanatory diagram, FIG. 5 is a loop gain characteristic diagram according to the present invention, and FIG. 6 is a configuration diagram of an embodiment for realizing the present invention. In the figure, 1- multiplier, 2- absolute value circuit, 3-- adder, 4-- feed bank coefficient multiplier, 6- integrator, 9-
- Multiplier for determining feed bank coefficient. Patent Applicant Fujitsu Ltd. Representative Patent Attorney Akira Yamatani Eisai 1 6 12 eyes 3 Zusai 4 Zusai 5z Ritsu 60

Claims (1)

[Claims] In an automatic gain control method in which an input signal is multiplied by a control signal to obtain a uniform output signal in a predetermined dynamic range regardless of changes in the input signal, the output signal is converted to an absolute value, and the output signal is converted to an absolute value, and the output signal is converted to an absolute value and the reference signal is a step of multiplying the difference with the output signal by a feedbank coefficient to obtain a feedback amount; a step of determining the control signal by obtaining an average value obtained by averaging the feedbank amount over time; and a step of determining the control signal based on the control signal. and changing the feedback coefficient.