JPH0329521A - Equalizer - Google Patents

Abstract

PURPOSE:To optimize a step filter corresponding to a wire material of a subscriber line and a wire diameter by validating plural filters being components of a step filter selectively so as to minimize an inter-code interference of a reception signal. CONSTITUTION:A level control section LC selectively forms a prescribed level control signal lc based on a peak value e0 of a reception signal extracted by a BT equalizer BTEQ when a transmission system including a digital subscriber line transmission equalizer LSI is made into a prescribed training mode and supplied to an automatic gain controlled amplifier AGCAMP. Thus, the entire gain of the system including the automatic gain controlled amplifier AGCAMP and a root f equalizer RTFEQ is automatically controlled to be a prescribed value. Thus, in case of not only the length of the line of the section, but the wire material or the wire diameter differ, the optimum filter is selected and designated, then the inter-code interference of the reception signal is suppressed and the error rate of a communication data is reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to equalization rhyme, for example, integrated service digital W4 (ISDN: Integra
-tad Services Digital Ne
equalization HLSI (La
rge Scale Integration:
Frequency axis equalization circuit (root f
This relates to technology that is particularly effective when used in applications such as equalizers. (Prior technology) There is an integrated service digital network that uses analog telephone transmission lines as subscriber lines. The integrated service digital network is equipped with subscriber line termination equipment provided corresponding to each subscriber line. These subscriber line termination devices include an equalizer LSI for digital subscriber line transmission. The equalizing HLSI for digital subscriber line transmission, for example,
As shown in Figure 1, a root f equalizer RTFEQ serves as a frequency axis equalizer for correcting the frequency characteristics of the subscriber line, and a plurality of branches (
BT (Bridged Tap) includes a BT equalizer BTEQ that serves as a time axis equalization device for eliminating intersymbol interference caused by echoes, etc. in Bridged Tap). Regarding the equalization opening t,si for digital subscriber line transmission,
For example, in November 1981, IEEE
Conference (National Teleco++n
Unicatlons Conference)
J: @E Page 1.5.1 to @E1.5.6. [Problems to be Solved by the Invention] In the integrated service digital network mentioned above, subscriber lines consisting of analog transmission lines exhibit different transmission characteristics depending on the line length. That is, the loss L of the subscriber line Lc, which has a relatively short line length, is small overall and exhibits a relatively flat frequency characteristic as shown in FIG. 8. Therefore, the subscriber line termination device The reception level of ecQ, that is, the peak value ecQ in time slot TO of reception fδf1, is
As shown in the figure, it becomes relatively large. On the other hand, the loss L of the subscriber line La, which has a relatively long line length, is large overall and exhibits a relatively steep frequency characteristic. Therefore, the reception level eao at the subscriber line terminal device is relatively small. In other words, when the subscriber lines have the same wire type, wire material, wire diameter, etc., the subscriber line termination equipment estimates the frequency characteristics of the subscriber line by determining the received fδ signal level and selects the optimal filter. Can be selected and specified. However, the equalizer L for digital subscriber line transmission in FIG.
In SI, based on the peak value 60 obtained by the BT equalizer BTEQ, the stamp filter control signal s f
c' and thereby the root f equalizer RTF
Controls the switching of the EQ stamp filter SF. However, when the wire materials or wire diameters of the subscriber line are different, the frequency characteristics of the subscriber line and the reception fδ in the subscriber line termination device are different.
The correlation with level eO collapses. For this reason,
As shown in Figure 1O, automatic gain controlled amplification! AG
Even after normalizing the reception level using CAMP and the equalizer RTFEQ and correcting the frequency characteristics of the subscriber line, intersymbol interference at each time front of the received signal is not sufficiently removed. As a result, equalization i! for digital subscriber line transmissions is obtained. The eye aperture of transmission systems including LSIs has been reduced, the S/N ratio has decreased, and the error rate of communication data has increased. An object of this invention is to provide a frequency-axis equalization system that can optimize a step filter depending on the wire material and diameter of the subscriber line.
Another object of the present invention is to increase the S/N ratio of a transmission system including frequency equalization and to reduce the error rate of communication data. The above and other objects and novel features of this invention include:
This will become clear from the description in this specification and the attached drawings. [Means for Solving the Problems] A brief overview of typical inventions disclosed in this application is as follows. That is, by performing a product-sum calculation of the amount of intersymbol interference in each time slot of the received fa signal and the corresponding weighting coefficient, the amount of intersymbol interference of the entire received signal is obtained, and in order to minimize this amount of intersymbol interference, This is used to control switching of step filters such as frequency axis equalizers. [Operation] According to the above-mentioned means, not only the line length of the subscriber line but also
Even if the wire material or wire diameter is affected, the optimal filter can be selected and specified in frequency axis equalization, etc., so the amount of intersymbol interference of the received signal can be suppressed. As a result, the S/N ratio of the transmission system including the frequency axis equalization path is improved, and the error rate of communication data is reduced. [Embodiment] FIG. 1 shows a block diagram of an embodiment of an equalizer dLs1 for digital subscriber line transmission to which the present invention is applied. In addition, FIG. 2 shows the equalization for digital subscriber line transmission shown in FIG. A conceptual diagram of an embodiment of the template filter control unit SFC included in iLsI is shown. moreover,
5 and 6, the root f equalizer R of FIG.
A characteristic diagram of one embodiment of three filters Fa to Fc provided in the step filter SF of TFEQ is shown. Based on these figures, the equalization Ji! for digital subscriber line transmission of this embodiment is calculated. This section provides an overview of the LSI structure and operation, as well as its characteristics. Note that the circuit elements making up each block in FIG. 1 are formed on a single semiconductor substrate such as single-crystal silicon using known semiconductor integrated circuit manufacturing techniques, although this is not particularly limited. The digital subscriber line transmission equalization LSI of this embodiment is included in a subscriber line termination device of an integrated service digital network whose subscriber line is an analog transmission line for telephones, although it is not particularly limited thereto. In this embodiment, the equalizer LSI for digital subscriber line transmission has a basic structure of a stored program type digital signal processing section, although this is not particularly limited. Therefore, the step filter control section S in FIG.
Equalization iLs for digital subscriber line transmission including FC
Most of the digital functions of each part of I are equivalently realized by the software of the digital signal processing part. In FIG. 1, a received signal IN transmitted through a hybrid circuit (not shown) of a subscriber line termination device is first converted into an equalization H for digital subscriber line transmission, although it is not particularly limited.
It is input to the prefilter PF of the LSI. The prefilter PF is designed to have a predetermined cutoff frequency that does not affect the amount of intersymbol interference, and removes high frequency noise of the received signal IN, as well as various types of wraparound noise, etc. It is transmitted to the gain control type amplification circuit AGCAMP. The automatic gain control type amplification system AGCAMP is basically based on a variable aftertenuator having a substantially flat frequency characteristic, although it is not particularly limited. The gain of this variable aftertenuator is controlled in minute steps according to the level control signal jc output from the level control section LC when the transmission system including the equalization sub-LSI for digital subscriber line transmission is in a predetermined training mode. This interpolates the gain stem of the root f equalizer RTFEQ. The automatic gain control amplifier AGCAMP also has an offset correction function, although this is not particularly limited. The level control unit LC is an equalizer P for digital subscriber line transmission.
When a transmission system including an iLSI is placed in a predetermined training mode, a predetermined level control a and jc are selectively applied based on a peak value eO of a received signal extracted by a BT equalizer BTEQ, which will be described later. , automatic gain control type increase! i device AGCAMP. This allows automatic gain control amplifier AGCAMP and root f equalizer RT
The overall gain of the system including FEQ is automatically controlled to a predetermined value. The output signal of the automatic gain control type amplification HAGCAMP is transmitted to the input terminal of a root f equalizer RTFEQ which is a frequency axis equalizer. The root f equalizer RTFEQ has
A step filter control signal s(c) having a predetermined number of bits is supplied from the step filter control unit SFC.The equalizer RTFEQ is not particularly limited, but includes three filters Fa to FC that are selectively enabled.
The basic configuration is a template filter SF that includes. As shown in FIG. 5, each of the filters Fa to Fc has a gain G that is increased in proportion to the frequency of the signal to be transmitted.
The slope of the gain is the steepest for the filter Fa, and the flattest for the filter Fc. These filters are
In the two planes, there is a zero point indicated by O mark in Fig. 6 and a pole point indicated by x mark, and the amount of the intersymbol interference is set by this. Root f equalizer RTFE (.a is the step filter control unit s when the transmission system including the digital subscriber line transmission equalizer Ht, sx is set to a predetermined tracing mode.
Step filter control tM s(c
Accordingly, the predetermined circuit constants are switched and the corresponding filters J"a to Fc are selectively enabled. Then,
When the transmission system is in normal communication mode, the received signal transmitted through the automatic gain control amplifier AGCAMP is subjected to predetermined frequency axis equalization processing according to the frequency characteristics of the effective filter. As a result, the frequency characteristics of the subscriber line are corrected, and the amount of intersymbol interference of the received fδ(a) is suppressed. At the same time, the step filter control section SFC and PLL circuit P
Supplied to LL. The step filter control unit SFC is
Although not particularly limited, as shown in FIG. 2, it is equivalently configured by a digital δ processing device to select and specify the optimum filter of the stamp filter SF of the root f equalizer RTFEQ. That is, in the equalizing HLSI for digital subscriber line transmission of this embodiment, the received signal Sr converted into a binary code by an A/D converter (not shown) is converted to a predetermined clock signal as shown in FIG. sampled according to Then, the sampling value in the time slot TO, that is, the peak value eO is taken as the received data, and the sampling value 61 to eO in the time slots T1 to T5 is
5 is the amount of intersymbol interference in each time slot. The step filter control unit SFC performs equalization 1i! for digital subscriber line transmission. When a transmission system including an LSI is set to a predetermined training mode, the intersymbol interference amount 6n is normalized based on the ratio between the intersymbol interference amount on and the peak value eO in each time slot, although it is not particularly limited. ”, and further, the multiplier MULT calculates the product of the absolute value 1en'l and the corresponding predetermined weighting coefficient αn, that is, α
Find n・Jan. Then, by calculating the product-sum operation, that is, Σαn+lon, through the read-only memory ROM and the arithmetic and logic unit ALU, the amount of intersymbol interference of the entire received signal is calculated, and the amount of intersymbol interference is minimized. , selectively shapes the step filter control signal sfc. As a result, the optimum filter is selected and specified in the step filter SF of the root f equalizer RTFEQ.The PLL circuit PLL receives the output signal Sr of the root f equalizer RTFEQ and extracts a certain fraction of the received signal. , forming a Kurofuku pulse CP. These clock pulses CP are not particularly limited to, but may be
The sampling pulse of the D conversion circuit, the clock of the digital signal processing section, etc. (provided as the M number).The BT equalizer BTEQ is not particularly limited, but it has five equalizers provided corresponding to the time slots 7 and 5. These tap coefficient words include the intersymbol interference at the corresponding time front of the received signal S' when the transmission system including the equalization HLsI for digital subscriber line transmission is in a predetermined training mode. A correction value corresponding to the amount is set empirically. When the transmission system including the equalization HLS (for digital subscriber line transmission) is in normal communication mode, the correction value set for each tap coefficient multiplier is as follows. It is output at the corresponding time front and subtracted from the received signal.As a result, the intersymbol interference of the received signal is canceled out, and only its peak value eO is extracted as the receiver signal.The output signal of the BT equalizer BTEQ is , the above peak value e
O, that is, received (R) data is sent out from the output terminal OUT of the equalization dLsI for digital subscriber line transmission, and is also supplied to the level control section LC.

As described above, the equalization dLsI for digital subscriber line transmission of this embodiment is included in the subscriber line termination equipment of a comprehensive digital service network whose subscriber lines are analog transmission lines for telephones, and is used to connect subscriber lines to Performs equalization processing on the frequency axis and time axis for the received signal transmitted through the Equalization HLSI for digital subscriber line transmission is based on frequency axis equalization
Equipped with equalizer RTFEQ, root f equalizer RT
FEQ consists of three filters Fa with different transfer characteristics.
to Fc7/)<step filters that are selectively enabled, and a step filter control unit SFC that selectively enables the filters Fa to Fc. In this embodiment, the step filter control unit SFC is
This is equivalently realized by a digital signal processing unit. Then, by performing a product-sum calculation of the amount of intersymbol interference in each time slot of the received signal and the corresponding weighting coefficient, the intersymbol interference #lit of the entire received signal is obtained, and steps are taken to minimize the amount of intersymbol interference. filter control signal sfc
form. As a result, the root f equalizer RTFEQ
With the step filter, the optimal filter is always selected and specified even when the length of the subscriber line, as well as the wire material and diameter, etc., are different. As a result, the S/N ratio of the equalized HLS1 for digital subscriber line transmission and the transmission system including it is improved, and the error rate of communication data is reduced. As shown in the above embodiment, by applying the present invention to the frequency axis equalization included in the equalization dLsl for digital subscriber line transmission of the subscriber IdA termination device of the integrated service digital network, the following can be achieved. You can obtain the following effects.
That is, (1) Find the intersymbol interference amount of the entire received signal by performing a product-sum operation of the intersymbol interference amount in each time slot of the received signal and the corresponding weighting coefficient, and calculate this intersymbol interference amount. By controlling the switching of step filters such as frequency-axis equalizers to minimize the This has the effect of being able to select and specify the optimal filter. (2) The above (11) provides the effect of suppressing the amount of intersymbol interference of the received signal. 《3》The above (1) and (2) allow equalization WLSI for digital subscriber line transmission, etc. (4) According to the above items <11 to (3), equalization for digital subscriber line transmission 1tnl L The effect is that the error rate of communication data in a transmission system including SI etc. can be reduced.The invention made by the present inventor has been specifically explained above based on the embodiments, but this invention can be applied to the above embodiments. It goes without saying that the invention is not limited to the example, and that various changes can be made without departing from the gist of the example. However, as shown in Fig. 3, it may be implemented in terms of hardware by actually combining several circuits.In other words, in Fig. 3, the step filter control section S
The FC has a basic configuration of a switch-on-passacitor, and is equipped with an integral open circuit consisting of a control section CONT and an operational amplifier AMP. As illustrated in FIG. 4, the control unit CONT generates a masked @signal m that is selectively formed by extracting the black component of the received fa signal Sr by the timing generation unit TG.
According to c, the integral filter is selectively activated, and the positive phase or negative phase integral process is selectively executed according to the sign classification signal sgn that is selectively expressed by determining the polarity of the received signal Sr. ．． Then, the step filter control signal sfc is selectively modified so that the result of these integral processes is minimized. In Figures 5 and 6, the step filter of the root f equalizer RTFEQ can be provided with any number of filters, and its frequency characteristics are as follows:
There are no restrictions imposed by this example. Furthermore, the equalizer LSI for digital subscriber line transmission may be partially equipped with the blocks shown in FIG. The calculation process of the amount of intersymbol interference by the step filter control unit SFC is as follows:
The weighting coefficient αn may not be used. Furthermore, the equalization H for digital subscriber line transmission shown in FIG.
Various embodiments may be adopted, such as the block structure of the LSI or the specific block structure of the step filter control unit SFC shown in FIGS. 2 and 83. The above explanation will mainly focus on the frequency axis included in the digital subscriber line transmission equalization product t, sI of the subscriber line termination device of the integrated service digital network, which is the field of application in which the invention made by the present inventor was made. Although we have described the case where the equalizer is applicable to an equalizer, it is not limited to this, and includes, for example, a device that can be used alone as a frequency axis equalizer, and a similar frequency axis equalizer. It can also be used in various semiconductor integrated circuit devices. The present invention is widely applicable to at least equalizers having a step filter as a basic structure and semiconductor integrated circuit devices including such equalizers. [Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly explained below. That is, in the frequency axis equalization included in the equalization HLSI for digital subscriber line transmission of the subscriber line termination equipment of the integrated service digital network, the amount of intersymbol interference at each time loft of the received signal and the corresponding weighting coefficient By calculating the amount of intersymbol interference of the entire received signal by calculating the sum of products of Even if they are different, the optimal filter can be selected and specified for frequency axis equalization, etc. As a result, the amount of intersymbol interference of the received signal can be suppressed, so the S/N ratio of the transmission system including equalization iLsI for digital subscriber line transmission can be improved and the error rate of communication data can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the equalizer JiiLSI for digital subscriber line transmission to which the present invention is applied. FIG. 2 is a block diagram of the equalizer LSI for digital subscriber line transmission shown in FIG.
A block diagram showing one embodiment of the step filter control section included in the SI, FIG.
A block diagram showing another embodiment of the step filter control section included in SI, Figure @4 is a signal waveform diagram showing one embodiment of the step filter control section of FIG. 3, and FIG. Or a frequency characteristic diagram showing an embodiment of the step filter control section in FIG. 3, and FIG. 6 is a Z frequency characteristic diagram showing an embodiment of the step filter control section in FIG.
Figure 7 is a waveform diagram showing an example of reception No. 1 in the equalized HLSI for digital subscriber line transmission in Figure 1, and Figure 8 is a diagram showing the loss in some analog transmission lines. FIG. 9 is a waveform diagram showing an example of the received signal transmitted via the analog transmission line of FIG. 8. FIG. The waveform diagram after normalization, @ll diagram, is the conventional equalization aL for digital subscriber line transmission.
It is a block diagram showing an example of s1. PF...Pre-filter, AGCAMP...Automatic gain control type increase III!
LC...Level control unit, RTFEQ...Root f equalizer, SF...Step filter, SFC...
...Step filter control section, PLL...PLL circuit, BTEQ...BT equalizer. ROM...read-only memory, MULT...multiplication section, ALU...arithmetic logic operation section. LV...Level judgment section, TG...Tie control generation section, CONT...Control section, AMP...Arithmetic amplifier. 1st rg Figure 2

Claims (1)

[Claims] 1. A step filter in which a plurality of filters having substantially different transfer characteristics are selectively enabled;
An equalizer characterized in that a plurality of filters constituting the step filter are selectively enabled so as to minimize the amount of intersymbol interference of the received signal. 2. The amount of intersymbol interference is evaluated by calculating the sum of products of the amount of intersymbol interference in each time slot of the received signal and the corresponding weighting coefficient. Equalizer described in section. 3. The equalizer according to claim 1 or 2, wherein the step filter is included in a frequency axis equalizer of an equalizer LSI for digital subscriber line transmission. .