JPS6126254B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an automatic line equalizer that corrects transmission waveform distortion due to transmission line characteristics. A conventional device of this type is shown in FIG. In the figure, 1 is an input terminal, 2 is an output terminal, and 3 is a pseudo-line network (BON), which is a network with characteristics equivalent to a line of a certain fixed distance.
4 is an adjustable line equalizer (AGC) that corrects line characteristics at various distances according to the control voltage. 5 limits the signal bandwidth with a roll off filter. A peak detector 6a detects the peak voltage of the output waveform. A differential amplifier 7a supplies a control voltage to the line equalizer 4 and forms a negative feedback path together with the peak detector 6a. Next, the operation of the circuit shown in FIG. 1 will be explained. Generally, the transfer characteristic G(l) of a transmission line is expressed by the following equation using the line length as a parameter. G(l)=EXP{-(α+jβ)l} α: Attenuation amount β: Phase amount l: Line length In addition, when expressed in decibels, the attenuation characteristic GA(l) of the transmission line is expressed as the square root of the frequency and the transmission distance l. It is proportional and is expressed by the following formula. ......Frequency l...Line length ₀ ...Normalized frequency lmax...Maximum equalization distance of equalizer 4 a...Line loss constant (i.e., = ₀ ,
Line loss for l=lmax) The variable line equalizer (√AGC) has the inverse characteristic of this line characteristic (so-called √ slope characteristic), and for example, the inverse function of G(l) is expressed as
An actual circuit is constructed by approximating with (l). As a result, the output waveform of No. 4 has transmission line distortion corrected. The roll-off filter 5 performs band limiting to remove unnecessary high frequency components.
An equalized waveform with good S/N and little intersymbol interference can be obtained at the output end 2. The peak detector 6a detects the peak value of the equalized waveform output, applies the detector output and a reference voltage (V ₁ ref) to two inputs of the differential amplifier 7a, and sends the amplified output to the variable line equalizer. Add as control voltage of 4. This feedback circuit controls the peak value of the equalized waveform output to be constant. Here, the variable line equalizer 4 corrects the line characteristics of each distance according to the control voltage,
Variable elements used in the circuit include variable capacitance diodes and the like. For example, when designing a frequency shifting type variable line equalizer using variable capacitance diodes, the capacitance needs to change in proportion to the square of the distance. Now, if the capacitance change ratio is C _v and the required maximum equalization distance of the variable line equalizer is lmax, then in an actual circuit, the variable range of the variable element is finite, so the line length that can be corrected is limited to the range of

This results in overequalization for [Formula]. In order to eliminate such overequalization for short distances, the conventional technology uses a pseudo line network 3 at the input end.
(BON) was installed. BON3 is a circuit network with characteristics equivalent to a line of a certain fixed distance.In this case, by setting BON3 to a line length equivalent to lmax/√Cv, the line automatic equalizer shown in FIG. However, the maximum equalization distance decreases. Conventional automatic line equalizers are configured as described above, so in a repeater system with uneven transmission spans, two types of repeaters must be used, one for short distances and one for long distances, at the time of installation. Another disadvantage is that it cannot be used in cases where the relay distance changes significantly due to bypassing of the transmission route after installation. This invention was made to eliminate the drawbacks of the conventional ones as described above, and by inserting a simple variable LPF (low-pass filter) at the input end, it is possible to reduce the transmission distance from zero with one type of repeater. The purpose of this invention is to provide an automatic line equalization device that can equalize a wide range of lines up to the maximum equalization distance of a variable line equalizer (√AGC). An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1 is an input terminal, 2 is an output terminal, and 4 is a variable line equalizer (√AGC) that corrects the line characteristics at various distances according to the control voltage. 5 limits the signal bandwidth with a roll-off filter. 6
a and 6b are peak detectors that detect the peak voltage of the output waveform. Reference numerals 7a and 7b are differential amplifiers that supply a control voltage and constitute a negative feedback path together with peak detectors 6a and 6b. 8 is a variable LPF whose characteristics change according to the control voltage from the differential amplifier 7b. Such a circuit has a configuration in which a feedback circuit is added to the conventional circuit shown in FIG. 1, which feeds back from the output side to the variable LPF 8 via the peak detector 6b and the differential amplifier 7b. Here 2
The reference voltage V ₁ ref of the two differential amplifiers 7a and 7b,
V ₂ ref have different values. Next, the operation will be explained. The variable line equalizer 4, roll-off filter 5, peak detector 6a, and differential amplifier 7a function in the same way as conventional ones,

It is controlled by a feedback circuit so that the peak value of the equalized waveform output at the output end 2 becomes constant at a distance of [Equation]. Here, the variable line equalizer 4 is set at the lower limit of the line length.

[Formula] can only be equalized, and at 0m the distance

[Formula] This results in considerable overequalization. To correct this, a variable LPF8 is installed at the input end. Variable LPF8 has line length

[Formula]

[Formula] It is necessary to approximate the corresponding line characteristics. The transfer function AL(l) of the variable LPF 8 is obtained by using the above T(l) as the variable line equalizer 4. becomes. When the variable LPF 8 is approximately realized by a simple first-order LPF with a fixed resistor R and a variable capacitance diode C, AL(l)=1/jw _CR +1 where the capacitance C is Therefore, it can be constructed with a simple variable primary LPF using a variable capacitance diode. The peak value of the equalized output waveform is detected by 6b, the detector output and the reference voltage (V ₂ ref) are applied to the two inputs of the differential amplifier 7b, and the amplified output is applied to the control voltage of variable LPF 8. In addition, the capacitance of the variable capacitance diode is changed. This feedback circuit controls the peak value of the equalized waveform output to be constant over a short distance. With this control, the variable LPF8 has a line length

It is possible to correct the over-equalization of the variable line equalizer 4 in [Equation]. Note that although a variable capacitance diode is used as the variable element in the above embodiment, other variable elements may be used.
Also, as an approximation function of the variable line equalizer,

Although [Formula] is used, other functions may be used. As described above, according to the present invention, the line automatic equalizer is configured by adding a variable LPF that corrects the short-range over-equalization characteristic of the variable line equalizer, so that it can be adjusted from zero meters with one type of device. This has the effect that line equalization over a wide range up to the maximum equalization distance of the line equalizer 4 can be automatically performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a conventional line automatic equalizer, and FIG. 2 is a block diagram showing an embodiment of the line automatic equalizer of the present invention. In the figure, 1 is an input terminal, 2 is an output terminal, and 3 is an input terminal.
is a pseudo line network (BON), 4 is an adjustable line equalizer (√AGC), 5 is a roll-off filter, 6 is a
a, 6b are peak detectors, 7a, 7b are amplifiers,
8 is a variable LPF. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 a variable low-pass filter placed at the input terminal and controlled by a control voltage obtained from the output signal;
A variable line equalizer whose input is the output of this variable low-pass filter and is controlled by a control voltage obtained from an output signal, a roll-off filter whose input is the output of this variable line equalizer, and this roll-off filter. control circuits that generate control voltages for the variable low-pass filter and the variable line equalizer, respectively, according to the output signal of the variable line equalizer, and the transmission distance is from the maximum equalization distance of the variable line equalizer to the lower limit of the line length. In the range, the variable line equalizer performs appropriate equalization according to the control voltage, and in the range where the transmission distance is zero from the lower limit of the line length of the variable line equalizer, the low-pass filter performs equalization according to the control voltage. An automatic line equalizer having an equalization function over a wide range from zero transmission distance to the maximum equalization distance of the variable line equalizer, which corrects the over-equalization amount of the variable line equalizer according to the above.