JPH0463005A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To reduce the influence of a pulsative single noise and to improve an S/N by controlling the amplification factor and offset of an amplifier based on the mean value and dispersion of an input signal. CONSTITUTION:The output signal OUT of the amplifier 2 is converted to a digital signal at an A/D converter 4, and is sent to a read only memory 5 as an address signal. An adder 7 adds one on data at the correspondent address of histogram memory 6 at every access to the histogram memory 6 by the read only memory 5. Such operation is repeated for a constant period decided in advance. A mean and dispersion detector 8 finds mean and dispersion from the histogram of the histogram memory 6, and multiplies them by a coefficient set in advance and sends them to the amplifier 2 as an offset control signal S and an amplification factor control signal G, respectively. Thereby, the S/N resistant for the pulsative noise can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic gain control device for electrical circuits such as measuring instruments in general, and particularly to an automatic gain control device for video signals.

[Prior art] Conventional automatic gain control is based on the maximum value of the human input signal (Vmax
) and the minimum value (Vmin), and send a feedback signal g as shown in the following formula to the amplifier.

[Problems to be Solved by the Invention] However, according to such prior art, the problem as shown in FIG.
The measured value of the maximum value V max or minimum value V min of the input signal fluctuates due to pulse noise as shown in a), which causes malfunction of automatic gain control.

In view of the problems of the prior art, an object of the present invention is to improve noise resistance in an automatic gain control device and prevent malfunctions caused by pulse noise.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an automatic gain control device that performs gain control of an amplifier based on an output signal of the amplifier. The amplifier is equipped with a circuit that outputs a signal representing the average and variance of the signal, and is used to control the gain of the amplifier.

[Effects] In this configuration, the amplification factor and offset of the amplifier are controlled based on the two statistics of the average value and variance of the output signal of the amplifier, so it is not affected by single-shot pulse noise. Therefore, gain control is performed without malfunctions caused by such noise.

[Example code] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a block diagram including an automatic cane control device according to an embodiment of the present invention. In the figure, 1 is an automatic cane control device, 2 is an amplifier, and 3 is a signal processing device.The automatic cane control device 1 outputs feedback signals S and G to the amplifier 2 based on the output signal OUT of the amplifier 2. Gain control is performed, and the controlled output of the amplifier 2 is output to the signal processing device 3.

4 is an A/ that digitizes the output analog signal of amplifier 2;
A D converter, 5 is a read-only memory whose address is the digital signal from the A/D converter 4, 6 is a histogram memory that stores a histogram based on the output of the read-only memory 5, and 7 is a histogram calculation in the histogram memory 6. The adder 8 is an average/variance detector that calculates the average/variance from the histogram in the histogram memory 6 and sends a command signal to the amplifier 2.

In this configuration, an input signal IN as shown in FIG. 2 is amplified to an appropriate level by an amplifier 2, and a signal processing device 3
sent to. At this time, the automatic gain control device 1 optimizes the amplification level of the amplifier 2.

In the automatic gain control device 1, the output signal OUT of the amplifier 2 is converted into a digital signal by the A/D converter 4 and sent to the read-only memory 5 as an address signal. The data read from the read-only memory 5 by this is the class value of the histogram, and becomes the address to the histogram memory 6. Each time the read-only memory 5 accesses the histogram memory 6 in this way, the adder 7 adds +1 to the data at the corresponding address in the histogram memory 6. Then, by reversing the above operation within a predetermined period of time, the second
A histogram as shown in FIG. 6(b) is created in the histogram memory 6.

Then, the mean/variance detector 8 includes a histogram memory 6
The average and variance are obtained from the histogram, multiplied by a preset coefficient, and sent to the amplifier 2 as an offset control signal S and an amplification factor control signal G, respectively.

According to this embodiment, (1) the dispersion value of the signal is used as feedback to the amplifier, so it is resistant to pulse noise. Furthermore, it is possible to easily remove values with low frequency on the histogram or values that deviate greatly from the distribution as abnormal values. (2) If the signal processing device 3 is a digital signal processing device, it is possible to share many parts such as an A/D converter with the automatic cane control device. Furthermore, (1) the automatic cane control device 1 is capable of controlling not only the amplification factor but also the offset voltage at the same time.

[Other Embodiments] Although the above embodiments involve A/D conversion,
It is also possible to consider a method in which processing is performed entirely by an analog circuit without performing /D conversion. FIG. 3 shows an embodiment using an analog circuit. The variance and average of the signal waveform required here are expressed by the following formula (1
) and (2).

(Average) (Variance) (2) FIG. 3 shows a circuit that implements these equations using an operational amplifier.

Equation (1) is realized by a circuit in which a gate circuit 32, an integrator 33, a multiplier 34, and a coefficient circuit 35 are connected in series, and the output signal OUT of the amplifier 2 is passed through this circuit to the offset control signal S to the amplifier ■. Become.

Equation (2) consists of a gate circuit 32, a multiplier 36, and an integrator 37.
, an adder 38 (here used as a subtracter), and a coefficient circuit 39 are connected in series, and the output of the multiplier 34 is input to the (-) terminal of the adder 38. The output signal 01JT becomes the gain control signal G to the amplifier 2 through this circuit.

[Effects of the Invention] As explained above, according to the present invention, since the amplification factor and offset of the amplifier are controlled based on the average value and variance of the human input signal, it is possible to avoid the influence of pulsed single-shot noise. This reduces noise and improves noise resistance.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a circuit including an automatic gain control device embodying the present invention, and FIGS. 2(a) and (b) show examples of human input signals in the device of FIG. 1 as time changes and histograms. FIG. 3 is a block diagram of a circuit including an automatic gain control device according to another embodiment of the present invention. 1: automatic gain control circuit, 2: amplifier, 3: signal processing device, 4: A/D converter, 5: memory dedicated to a output, 6
: Histogram memory, 7: Adder, 8: Average/variance detector, 32: Gate circuit, 33: Integrator, 34: Multiplier, 35: Coefficient circuit, 36: Multiplier, 37; Integrator, 38
: Adder, 39: Coefficient circuit. patent applicant

Claims (1)

[Claims] (1) An automatic gain control device that controls the gain of an amplifier based on the output signal of the amplifier, and includes a circuit that outputs a signal representing the average and variance of the output signal of the amplifier, and a circuit that outputs a signal representing the average and variance of the output signal of the amplifier. An automatic gain control device characterized in that the gain control of an amplifier is performed using the following.