JPS646576B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for performing automatic equalization with high accuracy in a PCM transmission repeater.

An example of a repeater in conventional PCM transmission will be explained using FIG. The encoded pulse after passing through the transmission line 1 is subjected to waveform distortion and attenuation due to the loss-frequency characteristics of the transmission line. Therefore, the equalizing amplifier 2 compensates for waveform distortion and attenuation caused by the transmission line 1. The pulse after equalization and amplification is determined by the identification regenerator 3 as to whether or not it is a pulse, and a predetermined pulse waveform is sent out. At this time, the timing section 4 generates a clock and provides information for controlling the pulse discrimination point and the sending pulse interval. The equalizing amplifier 2 uses a slope gain AGC ( automatic gain control). If this equalization amplification is ideally performed, an optimal identification waveform will be obtained and intersymbol interference will also disappear.

An example of the configuration of the equalizing amplifier 2 described above is shown in FIG. This section consists of a slope gain amplifier 5 for obtaining a slope gain, a peak value detection circuit 6 for making the equalized waveform peak value constant, and a rectifier circuit 7 for identification and reproduction.
and perform equalization amplification using the DC amplifier circuit 8,
Compensation is made only for transmission loss due to changes in transmission distance.

By the way, the transmission system may be affected by differences or changes in the transfer function from the output terminal of the preceding repeater to the equalization amplifier section via the transmission line due to the type of cable used, cable temperature fluctuations, pulse amplitude fluctuations sent from the preceding repeater, etc. The change in loss characteristics differs from the change in transmission loss characteristics due to the distance change described above. For this reason, it becomes difficult to perform equalization amplification with high accuracy in a form that makes it easy to identify and reproduce losses in the transmission system over the entire transmission band. In particular, in high-efficiency code transmission, differences (dispersions) and fluctuations in loss characteristics in the low frequency region of the transmission system cause large intersymbol interference degradation.

Specifically, in the block code format of a high-efficiency code (a code format that converts a binary code of a certain unit to a code of a shorter unit), for example, a 4B3T code, a 4-bit binary code is converted to a 3-bit ternary signal. Therefore, the repetition period of the bits to be sent becomes 3/4 (this makes it possible to use a transmission medium that could not be used due to the narrow transmission band). Among the equalization residuals in , the equalization residuals in the low frequency region greatly affect intersymbol interference for the following reasons. The 4B3T code has a flat power spectrum near _0/2 ( ₀ is the frequency corresponding to the pulse repetition period),
Compared to AMI code (Alternate Mark Inversion), etc., there are more frequency components around _0/2 .

Normally, equalizing amplifiers are subjected to roll off in order to reduce intersymbol interference. That is, a frequency band higher than _0/2 has high-frequency cut-off characteristics. As a result, it is necessary to pay attention only to frequency bands lower than _0/2 , and the quality of equalization greatly affects intersymbol interference.

For this reason, (a) residual equalization in the low frequency region due to conventional average equalization, or (b) differences and fluctuations in the loss characteristics of the transmission medium in the low frequency region, resulting in deterioration of intersymbol interference in the 4B3T high-efficiency code. It is the main cause of

The above explained the case of 4B3T code, but
The band that is the main cause of quality deterioration (deterioration of intersymbol interference) differs depending on the equalization format, the transmission code format, or the difference (dispersion) or variation in the loss characteristics of the transmission medium.

In order to solve these drawbacks, the present invention adds a local equalization deviation compensation function to enable high-precision equalization.The automatic equalization method in the low frequency region will be explained below. .

An embodiment of the invention is shown in FIG.

In FIG. 3, 2 is an equalization amplifier, 3 is an identification regenerator, 10 is a low frequency component detection circuit, 7 is a rectifier circuit, 11 is a comparison/amplification circuit, and 12 is a variable equalization circuit that performs narrowband equalization. It is a net.

The encoded pulse affected by the loss-frequency characteristics of the transmission path is amplified by the equalizing amplifier 2, and the identification/regenerator 3 identifies the presence or absence of a code and generates a rectangular wave sending pulse.

The equalizing amplifier 2 compensates for the loss characteristics of the cable, but it cannot achieve complete equalization, and generally,
Deterioration remains.

In order to further compensate for the equalization residual of this equalization amplifier, the rectangular output of the discrimination regenerator 3 is transferred to the variable equalization circuit network 1.
2, a correction signal is created using the control signal from the comparator/amplifier circuit 11, and after being added to the input signal from the input terminal 103, it is input to the equalizing amplifier 2.

The control signal of the variable equalization network 12 is transmitted to the equalization amplifier 2.
After branching the signal from the output terminal 104 and detecting the low frequency signal by the low frequency component detection circuit 10, the rectifier circuit 7 obtains the average value of the low frequency signal, and the average value signal is input to the comparison/amplification circuit 11. to create control signals.

The control signal operates such that when the equalization residual present at the terminal 104 is large, the variable equalization circuitry 12 outputs a large correction signal, and when the equalization residue is small, it outputs a small correction signal.

Next, in order to efficiently eliminate the equalization residual, it is necessary to extract the frequency components of the equalization residual signal. The equalization residual is usually expressed in the frequency domain, and is expressed as G()
If the waveform on the time axis is g(t), it can be expressed as G()=∫ ^∞ _-∞ g(t)e ^-j2 〓 ^t dt.

That is, since the equalization residual G( ) is expressed by the integral value of the instantaneous value of the time axis waveform, it is necessary to detect the integral value of the signal in order to accurately detect the equalization residual.

The rectifier circuit 7 can obtain an integral value by rectifying and smoothing the low frequency component signal selected by the low frequency component detection circuit 10. Therefore, an accurate equalized residual signal can be obtained.

With the configuration described above, it becomes possible to perform automatic equalization that can sufficiently compensate for differences in loss-frequency characteristics due to transmission line cable types, cable temperature fluctuations, etc., which could not be adequately compensated for in the past.

That is, in this Figure 3, especially when the PCM transmission repeater has at least a 2R (waveform equalization reshaping, identification reproduction regenerating) function,
By extracting control information from the identification regenerator 3, which is the output stage of the repeater, it is possible to control the output of the preceding repeater, the transmission medium, and the output of the target repeater to have constant characteristics. This differs from the case where a high-precision system is constructed using only the equalization amplifier 2, and a high-precision equalization system including the discrimination regenerator 3 in addition to the equalization amplifier 2 is constructed. The reason why the output from the preceding repeater to the output of the target repeater can be controlled to a constant characteristic is that the pulse output amplitude value of the identification regenerator is the same in all repeaters, regardless of waveform equalization (Reshaping).

As explained above, by carrying out the present invention, it is possible to obtain a high A precision automatic equalization system can be realized.

Regarding the present invention, we have described an automatic equalization method with an added local equalization amplification function in the low frequency region.
Similarly, it is also possible to realize a high-precision automatic equalization system that includes a local equalization amplification function in frequency regions other than low frequencies.
The present invention also enables high-precision equalization operations for equipment in other fields that include an equalization amplification function.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a repeater in a general PCM transmission system, FIG. 2 is an example of the circuit configuration of an equalizing amplifier therein, and FIG. 3 is a circuit configuration of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Transmission line, 2...Equalizing amplifier, 3...Discrimination regenerator, 4...Timing section, 5...Slope gain amplifier, 6
...Peak value detection circuit, 7.. Rectification circuit, 8.. DC amplifier circuit, 9.. Variable circuit, 10.. Low frequency component detection circuit, 11.. Comparison/amplification circuit, 12.. Variable equalization circuit network.

Claims (1)

[Claims] 1. An equalization amplifier having a √ characteristic that equalizes an input signal in which energy is concentrated in the low frequency part, an identification regenerator that regenerates a pulse signal from the output of the equalization amplifier, and an output signal of the identification regenerator. a narrowband variable equalizer circuit that inputs a signal and outputs an equalization signal to be added to the input signal of the equalization amplifier and equalizes the low frequency part of the input signal; a low-frequency component detection circuit that detects the low-frequency component; a rectifier circuit that rectifies the low-frequency signal detected by the low-frequency component detection circuit; and a rectifier that compares and amplifies the signal rectified by the rectification circuit with a reference level and outputs the result. An automatic equalization method characterized by comprising a comparison/amplification circuit that controls the variable equalization circuit with a signal.