JPS6249764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-stage AGC control method in an automatic equalizer that can expand the control range.

In wired transmission systems that use coaxial cables or pair cables as transmission media, the transmission characteristics of the cable change depending on the length of the section or fluctuations in ambient temperature, so an automatic equalizer is used to compensate for this at the repeater. Is required.

FIG. 1 shows an example in which the transmission performance of a cable is approximated by a broken line. As seen in the same figure,
If the transmission loss is small, use the linear linear approximation (6dB/
oct), but when the transmission loss exceeds a certain level, it becomes necessary to approximate it by a quadratic polygonal line approximation (12 dB/oct), and therefore, the equalization method for compensating for such cases generally becomes complicated.

Conventionally, as an equalization method in such a case, a method has been used in which variable equalizers are connected in series and their gain characteristics are combined. FIG. 2 is a block diagram showing the configuration of a multi-stage AGC system in a conventional cascaded automatic equalizer. In the figure, an input signal e _i at an input terminal 1 passes through a variable equalizer 2 , a preamplifier 3 , a variable equalizer 4 , and a post-amplifier 5 in sequence, and generates an output signal e ₀ at an output terminal 6 . The output signal e ₀ has its peak value detected by a peak detector 7, producing a DC signal proportional to the peak voltage. This DC signal is amplified by a DC amplifier 8 and then applied to variable impedance elements 9 and 10 to change their impedance values. As a result, the variable equalizers 2 and 4 change their frequency characteristics and gains, respectively. Therefore, between the input terminal 1 and the output terminal 6, a characteristic that is a combination of the gain characteristics of both variable equalizers appears.

FIG. 3 is a diagram illustrating the synthesis of broken line characteristics by cascading such equalizers. In Figure 3a, , , represents the gain characteristics that can be realized by the first variable equalizer, and ', ', ' represent the gain characteristics that can be realized by the second variable equalizer. ing. FIG. 3b also shows the first variable equalizer and the second variable equalizer.
A shows the composite characteristics obtained by cascading the variable equalizers of FIG.
It shows the characteristics obtained by synthesizing Doto' and C and Do', respectively.

When cascading variable equalizers in this way,
The sharing of the equalization characteristics of each equalizer can be changed to some extent by selecting the constant of the characteristic determining element in each variable equalizer, and by changing the variable impedance of each variable equalizer equally. Therefore, it is possible to configure the composition characteristic in the cascaded state to change as desired depending on the magnitude of the input signal. However, in the case of the configuration shown in FIG. 2, there is a limit to the equalization range of the composite characteristics only by changing the element constants, and it is not necessarily possible to realize ideal composite characteristics. Therefore, it was not possible to sufficiently increase the equalization accuracy of the equalizer.

The present invention attempts to eliminate such drawbacks of the prior art, and its purpose is to individually provide impedance values in variable impedance elements that control each variable equalizer, thereby controlling each variable equalizer. It is an object of the present invention to provide a multi-stage AGC control method for an automatic equalizer, which can freely select the characteristic change realized by the equalizer and widen the equalization range in the composite characteristic. In order to achieve this objective, the multi-stage AGC control method in the automatic equalizer of the present invention includes variable impedance elements whose impedance values change according to the signal from the peak detector that detects the peak value of the output. In an automatic equalizer consisting of multiple variable equalizers connected in cascade, the gain characteristics of which change according to changes in the impedance value of the impedance elements, the variable impedance elements of the variable equalizers at each stage are By equipping each DC amplifier to amplify the signal and giving unique input/output characteristics to each of these DC amplifiers, when the peak value of the peak detector is large, flat characteristics and linear characteristics occur as the frequency increases. It is characterized by obtaining a transmission characteristic that changes to a broken line approximation characteristic, and when the peak value is small, a transmission characteristic that changes to a flat characteristic, a first order broken line approximation characteristic, and a second order broken line approximation characteristic as the frequency increases. .

Examples will be described below.

Figure 4 shows the multi-stage automatic equalizer of the present invention.
FIG. 2 is a block diagram showing the configuration of an embodiment of an AGC control method. In the figure, symbols 1, 2, 3, 4,
The representations of 5, 6, and 7 are the same as in Figure 2. 11, 12 are DC amplifiers, 13, 14
is a variable impedance element.

In Fig. 4, the input signal e at input terminal 1
_i is added to variable equalizer 2. variable equalizer 2
has a variable impedance element 14 externally connected to it and has a gain characteristic determined by the value of the variable impedance element 14.
Variable impedance element 14 is controlled by the output of DC amplifier 12 to change its value. In this way, the variable equalizer 2 has a flat characteristic of different gains, for example, a gain characteristic as shown in FIG. It shows changing characteristics as shown in Figure 3a. In this case, 1
The second-order line characteristic has a certain frequency, for example, a band frequency.
When set to ₀ , the equalization characteristic is improved by reducing the frequency from _0/2 with a roll-off characteristic.

The output of the variable equalizer 2 passes through a preamplifier 3, undergoes constant amplification, and then is input to a variable equalizer 4.
The variable equalizer 4 has a variable impedance element 13 externally connected which is controlled by the output of the DC amplifier 11, and has a gain characteristic determined by the value of the variable impedance element 13. That is, a characteristic consisting of a combination of a flat characteristic of different gains and a characteristic that increases with a slope approximating a first-order polygon line above a certain frequency, for example, a characteristic as shown in ', ', ' in FIG. 3a is exhibited. In this case as well, the equalization characteristic is improved by reducing the first-order linear characteristic due to roll-off characteristic at frequencies _{of 0/2} or higher.

The output of the variable equalizer 4 is amplified to a certain degree by a post-amplifier 5 and then outputted from an output terminal 6. The peak value of a portion of the output from the output terminal 6 is detected by a peak detector 7 to generate a DC signal proportional to the peak voltage. This DC signal is amplified by DC amplifiers 11 and 12, respectively, and variable impedance elements 13 and 14 are respectively amplified as described above.
control.

Therefore, between the input terminal 1 and the output terminal 6, the characteristics of the variable equalizers 2 and 4 are superimposed to show a composite characteristic as shown in FIG. 3b, in which characteristics A and B are flat characteristics. Characteristic C shows a characteristic consisting of a combination of a flat characteristic, a first-order broken line approximation characteristic, and a second-order broken line characteristic. In both cases, the frequency
_0/2 or more is reduced due to roll-off characteristics, and specialization characteristics are improved.

In this case, the selected gain characteristic is determined by the peak value of the output. Therefore, when the transmission loss is small and the input signal is large and the peak value of the output signal is large, the gain is small, and when the transmission loss is large, the gain is large. Show advantage. That is, in Fig. 3a, the characteristics, and ', ', ' respectively indicate the gain characteristics when the transmission loss increases sequentially,
Therefore, the composite characteristics A, B, and C shown in FIG. 3b also show gain characteristics when the transmission loss increases sequentially. And when the transmission loss increases, the composite characteristic is flat when the frequency is low. Above the frequency, it is a linear linear characteristic and the gain increases with frequency. At low frequencies, the composite characteristic is flat, and above a certain frequency it becomes a linear characteristic. It becomes a polygonal characteristic, and at higher frequencies, it shifts to a quadratic polygonal characteristic.

In the conventional automatic equalizer configuration as shown in FIG. Since they are the same, there is a limit to the range in which the synthetic properties can be changed, and it is difficult to change them over a sufficiently wide range. However, according to the multi-stage AGC control method of the automatic equalizer of the present invention shown in FIG. 4, a DC amplifier is separately provided for each variable impedance element, and the magnitude of the control voltage can be arbitrarily selected. Therefore, the synthetic properties can be changed freely, and desired properties can be easily achieved.

FIG. 5 shows an example of _the impedance characteristics _{of the} variable impedance element. The impedance characteristic Z ₂ (e ₀ ) with respect to the output voltage e ₀ can be changed from the characteristic shown by the solid line to the characteristic shown by the chain line, and then to the characteristic shown by the dashed line, and therefore these variable impedance elements By controlling each variable equalizer and combining the characteristics, an arbitrary composite characteristic can be selected.

In the embodiment shown in FIG. 4, there are two variable equalizers.
Although the case of stages has been described, it goes without saying that three stages or even more stages may be used.

As explained above, according to the multi-stage AGC control method in the automatic equalizer of the present invention, it is possible to select equalization characteristics from a wide range of combinations of flat characteristics, first-order broken line characteristics, and second-order broken line characteristics. , excellent effects can be obtained.

[Brief explanation of the drawing]

Figure 1 shows an example of a broken line approximation of cable transmission characteristics, and Figure 2 shows the multi-stage approximation of a conventional automatic equalizer.
A block diagram showing the configuration of the AGC control system, FIG. 3 is a diagram explaining the synthesis of broken line characteristics, and FIG. 4 is a block diagram showing the configuration of an embodiment of the multi-stage AGC control system in the automatic equalizer of the present invention. FIG. 5 is a diagram showing the impedance characteristics of the variable impedance element. 1... Input terminal, 2... Variable equalizer, 3... Preamplifier, 4... Variable equalizer, 5... Post amplifier, 6... Output terminal, 7... Peak detector, 8...
...DC amplifier, 9, 10... Variable impedance element, 11, 12... DC amplifier, 13, 14...
...Variable impedance element.

Claims (1)

[Claims] 1. A plurality of variable equalizers each having a variable impedance element whose impedance value changes according to a signal from a peak detector that detects the peak value of the output, and whose gain characteristics change according to changes in the impedance value of each variable impedance element. In an automatic equalizer formed by connecting equalizers in cascade, each variable impedance element of the variable equalizer in each stage is equipped with a DC amplifier that amplifies the signal from the peak detector, and the input/output characteristics of each DC amplifier are By giving each of them uniquely, when the peak value of the peak detector is large, the flat characteristic and 1
It is characterized in that it obtains a transmission characteristic that changes into a second-order broken line approximation characteristic, and when the peak value is small, a transmission characteristic that changes into a flat characteristic, a first-order broken line approximation characteristic, and a second-order broken line approximation characteristic as the frequency increases. Multi-stage AGC control method for automatic equalizer.