JPH03214913A - Gain control method - Google Patents

Abstract

PURPOSE:To make an output level of a gain controller stable at a prescribed level almost in a definite time by decreasing stepwise an increasing and decreasing width of the gain in the case of decreasing the gain when an output of the gain controller exceeds a threshold level and in the case of increasing the gain when the output of the gain controller does not exceed the threshold level. CONSTITUTION:A signal processing section 6 gives an 8-bit digital output being a command of increasing a gain by (maximum value- minimum value of gain)/2 to a D/A converter 7, and then the D/A converter 7 controls a gain of an AGC amplifier 2. When an output voltage level exceeds a reference voltage level L4 of a comparator 5, the signal processing section 6 gives a command of decreasing the gain but the decreasing width is selected to be 1/2 of the preceding increase width. Similarly, the comparator 5 decides the gain increase or decrease, the change width is selected to 1/2 of the preceding change width and the processing proceeds in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gain control method for automatic gain control amplifiers and the like as gain controllers often used in measurement systems. [Prior Art] Conventionally, To perform automatic gain control (hereinafter referred to as AGC), when changing the gain according to the output of a comparator that determines whether the output of the AGC amplifier as a gain controller exceeds a certain threshold, the output In order to improve control accuracy, it is necessary to set the change in gain per unit time as small as possible.

[Problems to be Solved by the Invention] However, in this gain control method in which the change in gain per unit time is set small, the AGC
There was a problem in that it required a long time to follow large changes in the input of the amplifier.

In particular, immediately after the AGC operation starts, there is no past history, so
There is a problem that it may take a long time for the output level to stabilize to a certain level, and that time is also unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gain control method that can satisfy the contradictory demands of high stabilization accuracy of the output level of a gain controller and fast stabilization of the output level.

[Means to solve the problem]

To explain the means of the present invention for achieving the above object, the present invention provides a gain control method that automatically converges the output of the gain controller to a constant level by controlling the gain of the gain controller. It is characterized in that it is determined whether or not the output of the tora exceeds a certain threshold, and when the threshold is exceeded, the gain is lowered, and when it is not exceeded, the gain is increased and the increase/decrease range of the gain is gradually reduced. , [Function] When controlling the gain of the gain controller in this way, if the increase/decrease range is gradually reduced, the output level of the gain controller can be brought to a constant level in an approximately fixed time for any level of input signal. can be stabilized. In addition, the output level is highly stable and accurate.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows an example of an AGC amplifier that implements the gain control method of the present invention. In the figure, 1 is a signal input terminal, 2 is an AGC amplifier as a gain controller into which an input signal is input from signal input terminal 1, 3 is a signal output terminal for the output signal output from AGC amplifier 2, and 4 is a resistance component. A reference voltage generator that generates a reference voltage using a circuit, 5 a comparator that compares the output of the AGC amplifier 2 and the reference voltage from the reference voltage generator 4, and 6 a CPU to which the discrimination output of the hum comparator 5 is input. The signal processing unit 7 is a digital/analog converter (hereinafter referred to as a D/A converter) which receives the 8-bit digital output from the signal processing unit 6 and supplies a control voltage signal to the control voltage signal input terminal of the AGC amplifier 2. be.

FIG. 1 is a schematic diagram showing an example of the control operation of the gain control method of the present invention, in which Ll is AG
L2 is the output voltage level when the gain of C amplifier 2 is maximized, L2 is the output voltage level when the gain of AGC amplifier 2 is minimized, and L3 is the state where the gain of AGC amplifier 2 is half the maximum value and the minimum value. , and L4 indicates the reference voltage level of the comparator 5. Also, a~
e is each output voltage level when the gain of the AGC amplifier 2 is decreased stepwise by κ.

Next, an example of the gain control method of this embodiment will be explained using FIG. 1 and FIG. 2.

First, the gain of the AGC amplifier 2 at the start of the gain control operation is a certain value, and the gain of the AGC amplifier 2 at that time is a certain value.
Assume that the output voltage level of amplifier 2 is at point a.

Since this point a is at a lower level than the reference voltage level L4 of the comparator 5, the comparator 5 transmits a discrimination output that discriminates this state to the signal processing section 6. At this time, the signal processing unit 6 first calculates the gain (maximum value - minimum value)/
An 8-bit digital output, which is a command to increase the gain by a value of 2, is given to the D/A converter 7, which causes the D/A
Since the converter 7 controls the gain of the AGC amplifier 2, the output voltage level of the AGC amplifier 2 moves to point b. Since the output voltage level at point b exceeds the reference voltage level L4 of the comparator 5, the comparator 5 transmits a discrimination output that discriminates this state to the signal processing section 6. At this time, the signal processing section 6 issues a command to lower the gain, contrary to the previous time, and the amount of reduction is set to be κ of the previous increase amount. As a result, the output voltage level of AGC amplifier 2 is C
Move to a point. Thereafter, in the same way, comparator 5 determines whether the gain increases or decreases, and when the change width is set to κ of the previous change width and the operation is performed one after another, the output voltage level becomes the reference voltage level as shown at points d and e. Asymptotic to L4.

The stability accuracy of the output voltage level of the AGC amplifier 2 is within the change width of the final step. Note that the final step of gain control is based on the minimum resolution of the signal processing section 6 (for example,
1 bit).

The number of gain controls is determined by the maximum variable gain, final step gain, and change width, and the time required for the output voltage level to stabilize is always constant.

It is clear that the present invention operates in exactly the same way even if a variable attenuator is used as a gain controller.

Further, the change width for decreasing the gain stepwise can be realized without using κ.

When the range of gain change is set to κ or more, the number of times of gain control increases accordingly.

Further, once the output level of the gain controller can be maintained at a constant level as described above, it is also possible to switch to the normal AGC control mode and enter the normal AGC control operation.

[Effects of the Invention] As explained above, the gain control method according to the present invention reduces the increase/decrease range of the gain of the gain controller in stages, so that the gain control method according to the present invention gradually reduces the range of increase/decrease in the gain of the gain controller, so that it can be controlled in a substantially fixed time for input signals of any level. The output level of the gain controller can be stabilized at a constant level. Further, according to the present invention, there is an advantage that the stability accuracy of the output level is high. Therefore, according to the present invention, it is possible to satisfy the contradictory demands of high stabilization accuracy of the output level of the gain controller and high speed of stabilizing the output level. Furthermore, according to the present invention, highly accurate gain control can be completed in a shorter time than with conventional gain control methods.
It is also particularly useful in applications such as when it is desired to bring an unknown signal to a constant level in a short period of time in a start-up measurement system.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of the control operation of the gain control method of the present invention, and FIG. 2 is a schematic diagram showing an example of the control operation of the gain control method of the present invention.
It is a circuit diagram of a GC amplifier device. 2...AGC amplifier (gain controller), 4...
- Reference voltage generator, 5... Comparator, 6... Signal processing section, 7... A/D converter.

Claims (1)

[Claims] In a gain control method in which the output of the gain controller is automatically converged to a constant level by controlling the gain of the gain controller, it is determined whether the output of the gain controller exceeds a certain threshold, and if the output exceeds the threshold. A gain control method characterized in that when the gain is lowered at times, and when the gain is not exceeded, the gain is increased or decreased in steps.