JPH06177800A - Line equalizer - Google Patents

Abstract

PURPOSE:To provide a line equalizer not generating a discrimination error in a transmission code reproduction at the side of reception of two-wire type subscriber transmission device by a 2B1Q code transmission. CONSTITUTION:An analog input signal is amplified by a route f equalizer 10 which is initialized by a gain setting section 40, and then A/D converted by an A/D converter 20, and powered by a power arithmetic operation section 30. The gain of an inclination amplifier 11 of a route f equalizer 10 and a flat amplifier 12 are adjusted by a gain setting section 40. Then, the output signal from the route f equalizer 10 is inputted to a code-to-code interference detection section 50 detecting the distortion of the reception waveform. A value calculating a digital value from the detected distortion amount is received by the gain setting section 40 to adjust the gain of the inclination amplifier 11. The output is A/D converted again by the A/D converter 20, transmitting it to the next block.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line equalizer for a two-wire subscriber line transmission device using 2B1Q code transmission.

Conventionally, the subscriber cable has been mainly used for transmission of voice band signals, but in recent years, for the purpose of economically realizing ISDN, the subscriber cable transmits by expanding the frequency band for transmission. A digital transmission system has been developed, and a 144 kbit system as an information capacity is aimed at full-scale ISDN.

Actually, this information capacity of 144 kbit,
That is, the line bit rate of about 160 kbit / s is obtained by adding the frame bit and the monitoring bit to the information rate of 144 kbit / s.

Further, as a characteristic of the subscriber cable, in order to increase the flexibility of wiring in response to the demand for telephone calls, bridge taps with open ends are provided at various points along the transmission line. However, this bridge tap does not hinder the transmission of voice band signals.
In wideband signal transmission such as the bit method, an echo due to reflection of a bridge tap is generated, which is one of the causes of signal distortion on the receiving side, and an equalization function for this echo is required.

In addition, the transmission code to be applied includes bi-phase, AMI, and
Various codes such as 4A3T and 2B1Q have been considered.
In practical use, there is a demand for a two-wire subscriber transmission system that is less affected by the transmission line and has high transmission quality.

[0006]

2. Description of the Related Art An example of a conventional line equalizer will be described with reference to FIGS. FIG. 6 is a diagram showing an example of a signal waveform as a transmission signal, and FIG. 7 is a diagram showing an example of a conventional line equalizer.

In a two-wire subscriber line transmission apparatus using 2B1Q code transmission, in order to perform various types of line equalization, normally, a line or the like for performing gain setting as shown in FIG. 7 is calculated based on the result of power calculation of an input signal. A chemical device is required.

The 2B1Q code is the ideal 2 of (1) in FIG.
As shown by the eye pattern of the B1Q code, two digital signals generate one analog value. For example, 0V
If two + signs of the digital value are consecutive based on
"1" analog value, digital value "+3" for + code and -code, "-1" for -code and + code, and "-3" for continuous "-code". ,
It is an analog signal having a total of four values, with two values on both sides of + and −. The frequency of the digital signal is 160 KHz
Then, if the generated analog signal is "+" and "+" continuously, the transmission frequency becomes 80 KHz, and "+"
If "-" continues alternately, it becomes 40 KHz. Here, in order to detect the magnitude relationship of the signals on the receiving side, the √f equalizer 1 that initializes the input analog signal is used.
After being equalized to a certain level by 0, the A / D converter 2
At 0, a method is used in which an analog value is converted into a digital value, and the converted digital value is calculated as an average value of sum of squares by power calculation shown in the following mathematical formula.

The power calculation value P is

[0010]

[Equation 1]

However, N is the number of times of sampling, and AD is the sampling value of the input signal. Then, the gain setting unit 40 again adjusts the level of the equalizer 10 according to the result of the power-calculated value P, the A / D converter 20 converts the analog value into a digital value again, and the process proceeds to the next block. Send out.

[0012]

However, in a circuit such as the conventional example, intersymbol interference due to frequency cutoff in a low frequency band of a transformer using a transmitting side device, wraparound of a bridge tap in a transmission line, or the like is caused. As a result, the waveform of the received signal is distorted.

For this reason, when the power of a signal affected by intersymbol interference as shown in FIG. 6B is calculated, the intersymbol interference component indicated by a thin vertical line in the figure is also calculated. As a result, after comparing the power calculation result and the target power calculation value, the gain of the √f equalizer is set, so that the waveform distortion example of the received signal in the conventional example of FIG.
As shown in, for example, even if a code of "+3" is received,
Due to the influence of a large number of circuits, etc. passing through the middle of the received signal, the reception level was lowered, and a "tailing" phenomenon occurred in which the waveform was trailing on the opposite side based on 0V. In this case, even if the equalization of the received waveform is insufficient, the "tailing" part is also added as a result of the power calculation, and the power calculation result including the intersymbol interference component satisfies the target value. It will be. As a result, in the reception waveform determination unit of the next block, “+3” is originally 2
There is a problem that the B1Q code may cause a determination error as “+1”.

The present invention solves such a problem.
An object of the present invention is to provide a line equalizer that does not cause a determination error in reproduction of transmission code on the receiving side of a two-wire subscriber transmission device by B1Q code transmission.

[0015]

FIG. 1 shows an embodiment of the line equalizer of the present invention. In the figure, the same reference numerals as those in FIG. 7 indicate the same things, 60 is an intersymbol interference detection unit, and 70 is an adder.

According to the present invention, an analog input signal on the receiving side of a two-wire subscriber line apparatus by 2B1Q code transmission of an analog signal is amplified by a predetermined value by a √f equalizer 10 initialized by a gain setting section 40. , A / D converter 20 converts an analog signal into a digital signal, and the power calculation unit 30 calculates the power of the digital signal.
In the gain setting unit 40, the gradient amplifier 1 of the √f equalizer 10
After adjusting the gains of 1 and the flat amplifier 12, the A / D converter 20 converts the analog signal into a digital signal again,
In the line equalizer for sending to the next block, the output of the √f equalizer 10 is branched to detect the amount of distortion that is generated on average over the entire received waveform due to intersymbol interference, and the detected distortion is detected. An intersymbol interference detection unit 50 is provided which converts the quantity into an analog value signal and a digital value signal and sends it out.

The gain setting section 40 receives the digital value signal of the distortion amount sent from the intersymbol interference detection section 50 and adjusts the gain of the gradient amplifier 11 of the √f equalizer 10. The purpose can be achieved by providing the function.

Here, as the first specific intersymbol interference detection unit 50, a band elimination filter 51, a buffer amplifier 52, and a bottom detector 53 are connected in series, and the buffer amplifier is connected. A diode D is connected between the connection point of 52 and the bottom detector 53 and the ground so that the direction from the ground to the connection point is the positive direction.

As the second specific intersymbol interference detection unit 50, the band stop type filter 51, the buffer amplifier 52, and the peak detector 54 are connected in series and to the ground. , The buffer amplifier 52 and the peak detector 5
The diode D may be connected between 4 and the connection point such that the direction from the connection point to the ground is the positive direction.

[0020]

According to the present invention, in the line equalizer, the √f equalizer 1
An intersymbol interference detection unit that detects, in the output of 0, the distortion amount that is generated on average over the entire reception waveform due to the intersymbol interference, converts the detected distortion amount into an analog value signal and a digital value signal, and sends the analog value signal and the digital value signal. By providing 50, when distortion occurs in the input analog signal, the DC bias-like distortion amount that is generated evenly over the entire reception waveform is converted into an analog value and the signal is inversely added to the input analog signal. The amount of static distortion can be offset and removed.

Further, the gain setting section 40 has a function of receiving the digital signal of the distortion amount sent from the intersymbol interference detection section 50 and adjusting the gain of the gradient amplifier 11 of the √f equalizer 10. As a result, when distortion occurs in the input analog signal, when a signal obtained by converting the DC bias-like distortion amount that has been averagely generated over the entire received waveform into a digital value is input to the gain setting unit 40, the DC bias-like distortion amount is obtained. Since the gradient amplifier 11 performs the gradient amplification by adding an amount corresponding to, it is possible to approximate the signal waveform sent from the transmitting side, and the accuracy of reproduction of the transmitting waveform on the receiving side becomes high.

Here, as a specific intersymbol interference detection unit 50, a band elimination filter 51, a buffer amplifier 52, and a bottom detector 53 are sequentially connected in series. Then, a diode D is connected between the connection point between the buffer amplifier 52 and the bottom detector 53 and the ground so that the direction from the ground to the connection point is the positive direction.

In this way, the band-stop filter 51 extracts the DC component and the highest frequency component of the input analog signal, and the buffer amplifier 52 loses the input analog signal in the band-stop filter 51. The input analog signal is prevented from interfering with the diode D inserted between the ground and the amplifier.

The output of the buffer amplifier 52 is connected to the ground by a diode D inserted between the ground and the buffer amplifier 52.
Half-wave rectification is performed on the output signal of and the signal component in the positive direction is extracted. The signal component in the positive direction is input to the bottom detector 53 to detect the amount of DC component over the entire received signal. Since the detected value becomes the distortion amount, a digital value can be calculated from the detected value and supplied to the gain setting section 40.

As another method, as the intersymbol interference detection section 50, a band elimination filter 51 and a buffer amplifier 52 are provided.
And the peak detector 54 are sequentially connected in series. And a connection point between the buffer amplifier 52 and the peak detector 54,
The diode D is connected to the ground so that the direction from the connection point to the ground is the positive direction.

By doing so, the buffer amplifier 5
The half-wave rectified signal component in the negative direction can be extracted from the output signal of 2. Then, the half-wave rectified signal component in the negative direction is input to the peak detector 54, and the amount of the negative DC component generated over the entire received signal is detected. Since the detected value becomes the distortion amount, the digital value of the detected value can be calculated and supplied to the gain setting section 40.

[0027]

EXAMPLES Examples will be described with reference to FIGS. FIG. 2 shows a first specific example of the intersymbol interference detector of the present invention, and FIG. 3 shows a second embodiment of the intersymbol interference detector of the present invention. 4 is a flow chart of an embodiment using the first concrete example of the present invention, and FIG. 5 is a flow chart of an embodiment using the second concrete example of the present invention.

In the figure, the same reference numerals as those in FIG.
Reference numeral 51 is a band elimination filter (BEF), 52 is a buffer amplifier (BUFF AMP), 53 is a bottom detector, 54 is a peak detector having the same function as the bottom detector 53, and D is a diode.

First, the case of the embodiment constituted by the first specific example of the intersymbol interference detection unit of the present invention will be described with reference to FIGS. 1, 2 and 4. Note that the ◯ symbol shown in FIGS. 4 and 5 corresponds to the ◯ symbol shown in FIG. 1 and also corresponds to the ◯ symbol in the description of the flowcharts of the first concrete example and the second concrete example described below.

In FIG. 4, the gains of the gradient amplifier 11 and the flat amplifier 12 of the √f equalizer 10 are initialized by the gain setting section 40 in advance. The power of the input signal is calculated and the result P is obtained. P is the target minimum level (PUN) and the target maximum level (PUN)
It is determined whether it is within the range of OV). In, when the result of N is obtained, the tilt gain value variable width (ΔG1) and the flat gain value variable width (ΔG2) are changed,
√f Reset the gain value of the equalizer 10.

Then, At Y, when the result of Y is obtained, is VB shown in FIG. 2 (3) below the target maximum level (Vm)?
Determine whether or not.

However, in FIG. 2C, the input signal (eye pattern including the intersymbol interference component) is filtered by the band elimination filter 51.
After passing through, the gain is returned to the original level by passing through the buffer amplifier 52 of the gain that compensates for the loss in the band rejection filter 51, and the negative side is blocked by the diode D connected to the ground. Then, bottom detection is performed to detect the intersymbol interference component (VB). If the result is N, the gain value of the gradient amplifier 11 is increased by one step (ΔG2), and the waveform of the input signal affected by the intersymbol interference is further shaped. If the result is Y, it means that the processing is completed.

Similarly, referring to FIGS. 1, 3 and 5,
An outline of the case of the embodiment constituted by the second specific example of the intersymbol interference detection unit of the present invention will be described. In FIG. 5, the gain of the slope amplifier 11 and the flat amplifier 12 of the √f equalizer 10 is initialized by the gain setting unit 40 in advance. The power of the input signal is calculated and the result P is obtained. P is the target minimum level (PUN) and the target maximum level (PUN)
It is determined whether it is within the range of OV). In, when the result of N is obtained, the tilt gain value variable width (ΔG1) and the flat gain value variable width (ΔG2) are changed,
√f Reset the gain value of the equalizer 10.

Then, In the case of the result of Y, whether VP shown in FIG. 3 (3) satisfies the target maximum level (Vc) or more,
Determine whether or not.

However, in FIG. 3C, the input signal (eye pattern including intersymbol interference component) is filtered by the band elimination filter 51.
, The gain is returned to the original level by passing through the buffer amplifier 52 having a gain of 1 to 2 which compensates for the loss in the band elimination filter 51, and the diode D connected between the ground and Cut off the positive side, and perform peak detection,
The intersymbol interference component (VP) is detected. If the result is N, the gain value of the gradient amplifier 11 is increased by one step (ΔG2), and the waveform of the input signal affected by the intersymbol interference is further shaped. If the result is Y, it means that the processing is completed.

As described above, the amount of distortion can be detected in the same manner regardless of which of the first concrete example and the second concrete example is used, and therefore the circuit may be constructed using either one.

[0037]

As described above, according to the present invention,
Since line equalization can be realized on the basis of the result of power calculation of the received signal without being affected by intersymbol interference, improvement in transmission quality can be expected.

[Brief description of drawings]

FIG. 1 is an embodiment of a line equalizer of the present invention.

FIG. 2 is a first specific example of the intersymbol interference detection unit of the present invention.

FIG. 3 is a second embodiment of the intersymbol interference detection unit of the present invention.

FIG. 4 is a flowchart of an embodiment using the first specific example of the present invention.

FIG. 5 is a flowchart of an embodiment using the second specific example of the present invention.

FIG. 6 is a diagram showing a signal waveform as a transmission signal.

FIG. 7 is an example of a conventional line equalizer.

FIG. 8 is a diagram showing an example of waveform distortion of a received signal in a conventional example.

[Explanation of symbols]

 10 √f Equalizer 11 Gradient Amplifier 12 Flat Amplifier 12 A / D Converter 30 Power Calculation Section 40 Gain Setting Section 50 Inter-Signal Interference Detection Section 51 Band Stop Filter (BEF) 52 Buffer Amplifier (BUFF AMP) 53 Bottom Detector 54 Peak detector

Claims (3)

[Claims] 1. An analog input signal on the receiving side of a two-wire subscriber line apparatus by 2B1Q code transmission of an analog signal is amplified by a predetermined value by a √f equalizer (10) initialized by a gain setting unit (40). After that, the analog signal is converted into a digital signal by the A / D converter (20), and the power of the digital signal is calculated by the power calculation unit (30), and based on the setting in the gain setting unit (40). Gradient amplifier (11) of the √f equalizer (10)
And the gain of the flat amplifier (12) are adjusted, the analog signal is converted into a digital signal again by the A / D converter (20), and the √f equalization is performed in the line equalizer for sending to the next block. The output of the device (10) is branched to detect the distortion amount that is generated on average over the entire reception waveform due to intersymbol interference, and the detected distortion amount is converted into an analog value signal and a digital value signal and sent out. Intersymbol interference detection unit (5
0) and the gain setting unit (40) includes the intersymbol interference detection unit (5
0), which has a function of receiving the digital signal of the distortion amount and adjusting the gain of the gradient amplifier (11) of the √f equalizer (10). . 2. The band-stop filter (51), the buffer amplifier (52), and the bottom detector (53) are connected in series as the intersymbol interference detector (50) according to claim 1. , And the buffer amplifier (5
A diode (D) is connected between a connection point between 2) and the bottom detector (53) and the ground so that the direction from the ground to the connection point is a positive direction. A line equalizer that does. 3. The band-stop filter (51), the buffer amplifier (52), and a peak detector (54) are connected in series as the intersymbol interference detection unit according to claim 1. And the buffer amplifier (5
The diode (D) is connected between the connection point of 2) and the peak detector (54) and the ground so that the direction from the connection point to the ground is a positive direction. A line equalizer that does.