JPS5851706B2 - automatic amplitude equalizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplitude equalization device when a general telephone line is used for data transmission such as a facsimile.

FIG. 1 shows a conventional equalizer in which an equalizer having a single characteristic is installed before the AGC circuit of a facsimile receiver.

The signal sent from the transmitting side is amplitude-equalized by an equalization amount of 1.

Furthermore, the amplification degree is controlled by the AGC circuit 2 to produce a signal adjusted to a constant level, and the signal is demodulated by the demodulator 3 to reproduce the video signal.

However, in this case, since the equalization amount 1 is fixed with a single characteristic, there is a drawback that the image quality varies depending on the attenuation characteristics of the line and is unstable.

The attenuation characteristics of a line are greatly influenced by the length of the cable section.

Particularly in high frequency bands, the longer the length of the cable section, the greater the amount of attenuation.

Furthermore, there is almost no change in attenuation in the low band.

That is, the slope of the attenuation characteristic changes depending on the length l of the cable section.

Therefore, sufficient equalization cannot be achieved if the degree of equalization is constant.

The present invention has been made in view of the above-mentioned drawbacks, and has a plurality of equalization amounts in advance, and automatically determines the optimum amplitude by using the level of the feedback loop of the AGC circuit that is downstream of these equalization amounts. It is an object of the present invention to provide an automatic amplitude equalization device that can select an equalizer.

The present invention will be explained below based on the drawings.

FIG. 2 is a block diagram showing one embodiment of the present invention.

4 is a terminal for inputting a signal from the transmitting side, 5a to 5c are amplitude equalizers, and the degree of equalization increases in the order of a, b, and c.

6 is an AGC circuit, which performs gain control of the signal from the switching circuit 7.

Note that 8 is a feedback loop of the AGC circuit 6.

A hold circuit 9 holds the level of the feedback loop 8 appropriately amplified by the amplifier 10.

Reference numeral 11 denotes a discrimination circuit, which compares and discriminates the output level of the hold circuit 9 and the output level of the amplifier 10.

12 is a control circuit, switching circuit γ and 13
and controls the alarm circuit 14.

Next, the operation will be explained.

First, a low frequency first signal is input from the transmitting side through the terminal 4.

At this time, the switching circuit 7 inputs the input signal to the AGC circuit 6 without equalization.

The level appearing in the feedback loop 8 of the AGC circuit 6 is appropriately amplified by the amplifier 10 and held in the hold circuit 9 via the switching circuit 13.

Subsequently, a high frequency second signal is inputted to the terminal 4 from the transmitting side.

Like the first signal, this signal is also input to the AGC circuit 6 via the switching circuit 7 without equalization.

At this time, the switching circuit 13 is on the discriminating circuit 11 side, and the level of the feedback loop 8 of the AGC circuit 6 is input to the discriminating circuit 11 via the amplifier 10.

The level from the halt circuit 9 is also input to the discrimination circuit 11, and these two levels are compared.

When this level difference is significant, the control circuit 12 is operated to connect the switching circuit 7 to the flower vase 5a.

By this switching of the switching circuit 7, the second signal from the transmitting side is inputted to the AGC circuit 6 through the flower vase 5a.

At this time, the level of the feedback loop 8 of the AGC circuit 6 is amplified by the amplifier 10 as described above, and then compared with the level of the hold circuit 9 by the discrimination circuit 11.

If this level difference is still large, the control circuit 12 is further operated to connect the switching circuit 7 to the flower vase 5b.

The above operations are repeated in sequence, and when the two levels input to the discrimination circuit 11 become approximately the same, the switching of the switching circuit 7 is stopped.

The iso-vase selected at this time is the optimal iso-vase.

If the difference between the two levels input to the discrimination circuit 11 is larger than a predetermined difference even if the iso-vase with the highest degree of equalization (iso-vase 5c in FIG. 2) is used, the line will be abnormal. This can be determined and displayed by the alarm circuit 14 via the control circuit 12.

In this embodiment, the case where there are three amplitude equalizers has been described, but any number of amplitude equalizers may be used as long as there are a plurality of equalizers.

In the above embodiment, the expressions such as first and second signals are used, but they are signals that come in time series.

As explained above, according to the present invention, by preparing a plurality of amplitude equalizers with different characteristics and selecting the most suitable equalizer for the current line depending on the level of the feedback loop of the existing AGC circuit, It is possible to eliminate the signal distortion that conventionally occurred due to insufficient equalization, and it is possible to improve the recorded image quality in facsimile.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional equalizer, and FIG. 2 is a block diagram of an automatic amplitude equalizer according to an embodiment of the present invention. 5a-5c...amplitude equalizer, 6...A
GC circuit, 7.13...Switching circuit, 9
...Hold circuit, 11...Discrimination circuit, 12...Control circuit, 14...Alarm circuit.

Claims (1)

[Claims] 1. In a facsimile machine that records and plays back a recorded image signal from the transmitting side using a telephone line after passing it through an amplitude equalizer and an AGC circuit on the receiving side, multiple amplitude equalizers each having different equalization characteristics are used. and a hold circuit that holds the voltage of the feedback loop of the AGC circuit, and a discrimination circuit that compares the level of the hold circuit with the level of the feedback loop of the AGC circuit, and the first signal from the transmitting side. is input into the AGC circuit to hold the obtained feedback loop voltage in the hold circuit, and the second signal from the transmitting side is passed through any one of the plurality of amplitude equalizers or directly to the AGC circuit. The level input to the AGC circuit and the output level of the hold circuit at this time is compared with the output level of the hold circuit using the discrimination circuit, and the plurality of amplitudes are equalized until a predetermined level difference is satisfied. An automatic amplitude equalizer characterized by switching the amplitude equalizer.